Scientific and Regulatory Policy Committee Review

Abstract

In 2014, the Organisation for Economic Co-operation and Development (OECD) issued guidance no. 16, Guidance on the GLP Requirements for Peer Review of Histopathology. The stated purpose of the guidance document is “to provide guidance to pathologists, test facility management, study directors and quality assurance personnel on how the peer review of histopathology should be planned, managed, documented, and reported in order to meet Good Laboratory Practice (GLP) expectations and requirements.” On behalf of and in collaboration with the global societies of toxicologic pathology, the Society of Toxicologic Pathology initiated a review of OECD guidance no. 16. The objectives of this review are to provide a unified interpretation of the guidance, to recommend compliant processes for organizations to implement, and to avoid inconsistent process adaptations across the industry. This review of the guidance document is the product of a global collaboration with other societies of toxicologic pathology and provides a section-by-section international consensus view and interpretation of the OECD guidance on peer review.

Introduction

Guidance on the GLP Requirements for Peer Review of Histopathology (guidance no. 16) was issued by the Organisation for Economic Co-operation and Development (OECD) on September 26, 2014, and reissued on December 15, 2014 (OECD 2014a). The stated purpose of the OECD document is “to provide guidance to pathologists, test facility management, study directors, and quality assurance personnel on how the peer review of histopathology should be planned, managed, documented, and reported in order to meet Good Laboratory Practice (GLP) expectations and requirements.”

Guidance no. 16 is classified as an OECD advisory document. Historically, OECD advisory documents are drafted with limited input from stakeholders. The OECD GLP Working Group did allow input from stakeholder groups on two separate occasions, and the global community of toxicologic pathologists provided comment through the various international societies of toxicologic pathology before finalization of the guidance. Modifications to the draft versions before issuance of guidance no. 16 clearly reflected some incorporation of stakeholder input. Much of the final guidance is in line with published recommended practices (Morton et al. 2010); however, some sections appear inconsistent or unclear.

The purpose of this review is to provide a unified interpretation of the guidance and serve as a framework for organizations to modify their processes as needed to comply with the guidance. This review has been developed in collaboration with the international societies of toxicologic pathology in order to provide a consensus global view.

Review of OECD Guidance No. 16

This review is arranged into segments that correlate with the sections of the OECD guidance no. 16. For each segment, the italicized portion quotes the OECD guidance followed by text that provides an interpretation of the guidance by the global toxicologic pathology community.

While the majority of the OECD guidance is clear and consistent with the contemporary practices of peer review, there are components that may lend themselves to various interpretations. This review is intended to provide a unified and compliant interpretation of the guidance in the context of Morton et al.’s “Recommendations for pathology peer review” (2010). The 2010 Morton et al. peer review manuscript serves as the foundation for pathology peer review practices since it was globally endorsed by the Society of Toxicologic Pathology, the European Society of Toxicologic Pathology, the Japanese Society of Toxicologic Pathology, the British Society of Toxicological Pathology, the French Society of Toxicologic Pathology, the Italian Society of Toxicologic and Experimental Pathology, the Society of Toxicologic Pathology–India, the Korean Society of Toxicologic Pathology, the Latin American Society of Toxicologic Pathology, and the American College of Veterinary Pathologists.

For clarity, the following terminology and definitions are used:

“GLP” refers to Good Laboratory Practice (OECD 1998; U.S. Food and Drug Administration [U.S. FDA n.d.] Title 21 Code of Federal Regulations Part 58 [21 CFR 58]).

“Protocol” refers to the study protocol or plan, and any amendments.

“Peer review memo” is synonymous with the terms “peer review statement,” “peer review report,” and “peer review certificate.” It is recognized there are global nuances in how these terms are defined, as in Japan where “memo” is not a formal document and “statement” is the formal document.

“Finalized anatomic pathology report” refers to the signed and dated anatomic pathology report (which by implication indicates finalized histopathology diagnoses).

“Raw data” is considered the signed and dated final report of the pathologist (U.S. FDA 1987). There are nuances in how raw data is defined by global regulatory agencies, such as in Japan where raw data is considered the signed and dated locked histopathology diagnoses (Japanese Ministry of Health and Welfare [Japanese MHW] 1997). However, because of its clear definition and wide global application, the FDA definition will be used in this review.

“Study report” or “toxicology report” refers to the report gathering the results from the entire study, including the scientific contributing reports such as the anatomic pathology report.

Section 1. Background

• 1.1. The histopathological assessment of tissue samples is one of the key endpoints of a toxicology study, and the results obtained will contribute substantially to the outcome and conclusions of the study.

The finalized pathology report, which includes the results from the microscopic examination of tissue samples (histopathologic assessment), often plays a critical role in the conclusions of a toxicology study. Histopathologic assessment includes the primary pathologist review and often includes pathology peer review.

• 1.2. Because the assessment of tissue specimens is based upon the expert opinion of the slide reading pathologist, it is common for test facilities to have implemented a peer review process whereby a number of slides are assessed by a second pathologist. The process is a means of assuring the quality and the accuracy of interpretation and maintaining best practices. Although there is no absolute requirement in the GLP principles to conduct peer review, most receiving authorities expect that some level of peer review will be performed. This document is concerned with the processes used to organise, perform and record the results of this review.

Peer review is a fundamental tool in toxicologic pathology that has steadily developed over time. Although there is no requirement in the GLP principles (OECD 1998) or FDA GLP regulations (U.S. FDA 21 CFR 58) to conduct peer review, it is commonly practiced to ensure the quality and accuracy of the diagnoses and interpretations (Crissman et al. 2004; Mann and Hardisty 2013; Morton et al. 2010). While the peer reviewer can provide valuable insight, it is important to remember that the study pathologist is ultimately responsible for the interpretation of the pathology portion of the study and for placing it into context so that, in collaboration with the study director, conclusions for the study are drawn.

• 1.3. The peer review process can lead to changes in the interpretation of the slides and the reported results, and potentially the outcome and conclusions of the study. The purpose of this document is to provide guidance to pathologists, test facility management, study directors and quality assurance personnel on how the peer review of histopathology should be planned, managed, documented and reported in order to meet GLP expectations and requirements. This document is a complement to the guidance provided in section 3.6.3.7 of OECD Guidance Document 116, whose focus is on how histopathology peer review should be conducted.

This guidance document is specific to the peer review process (planning, management, documentation, and reporting) and augments current recommended practices on how to conduct a pathology peer review. The concepts and procedures for the conduct of histopathology peer review mentioned in Section 3.6.3.7 of OECD Guidance Document 116 (Guidance Document 116 on the Conduct and Design of Chronic Toxicity and Carcinogenicity Studies; OECD 2014b) are consistent with those previously described by Morton et al. (2010).

• 1.4. There may be particular studies where the study sponsor requires that some or all of the slides are reviewed by a specific peer reviewing pathologist. This may be because the reviewing pathologist is an established expert in a particular field of pathophysiology, or has particular experience of the physiological affects of the test item under investigation. This approach allows for consistency of finding terminology and interpretation throughout different studies which are investigating the effects of the same test item. It is acknowledged that relevant experts are not always employed by a GLP facility and consequently it may not always be possible to perform the peer review in a GLP compliant facility.

Situations may arise wherein peer reviews or additional slide reviews may be conducted in a non-GLP-compliant facility. This should be documented in the study protocol or amendments and report.

Section 2. GLP Requirements

• 2.1. Any requirements for peer review performed at the test facility or by external consultants, should be clearly described in the study plan or subsequent study plan amendments. This should include information on how the pathology peer review will be planned, managed, documented and reported. It should also be stated whether the review will be performed contemporaneously or retrospectively. If some or all of the above information is documented in an SOP a reference to the current version of the SOP would be acceptable.

The standard operating procedure (SOP) and/or protocol/protocol amendments should specify whether the review is contemporaneous (conventional) or retrospective (discussed subsequently). The peer review pathologist and his or her affiliation can be identified in a protocol, protocol amendment, or study documentation (e.g., peer review memo).

For clarity, the following distinctions for contemporaneous and retrospective peer reviews are provided:

A contemporaneous peer review is the conventional peer review that begins with the evaluation of a defined subset of histologic slides (specimens), draft pathology findings, and the draft narrative/interpretation. The review of these materials is generally completed before issuance of a finalized (signed and dated) anatomic pathology report and before histopathology diagnoses have been finalized (locked or signed). Since histopathology raw data is not established until the pathology report has been signed (which by implication indicates finalized histopathology diagnoses), the peer reviewer of a contemporaneous peer review is not generating raw data. The peer review pathologist should be able to confirm that the finalized pathology report accurately represents a consensus between the study and peer review pathologist. The peer review is generally documented after the pathology report is finalized by issuance of the signed and dated peer review memo. However, widely accepted global variations exist in the timing of the signature.

A retrospective peer review is initiated after the anatomic pathology report has been finalized (signed and dated), and as such has the potential to result in an alteration of histopathology raw data. Any changes are subject to an audit trail and are made in the form of an amended pathology report. Furthermore, the original signed pathology report must be retained. Retrospective peer reviews are often performed to address specific post hoc issues (whether a contemporaneous peer review was conducted or not) and should be designed, conducted, and documented to ensure that this process can be accurately reconstructed.

The detailed methods for conducting a peer review are commonly described in SOPs. If the SOP(s) of the peer reviewer’s organization will be used and the organization responsible for the peer review is referenced in the protocol, then additional references to the specific SOP(s) being used should not be required but could be referenced in the peer review memo. However, if another organization’s peer review SOP will be followed, the SOP should be referenced in the protocol or peer review memo. If the peer review method is not documented in an SOP, then the methods should be described in the study protocol. It is not recommended to list specific SOP numbers because it would be inconsistent with the overall management of SOPs within a study protocol. SOPs should define the minimal materials for an appropriate peer review and allow for sufficient flexibility in review of additional materials to achieve the peer review objectives. That is, the peer review pathologist should be able to review additional materials as appropriate based on the findings in a study. The specific details of the evaluation should be documented within the peer review memo.

An important concept of peer review, audit trail, and documentation of changes hinges on the concept of what constitutes pathology raw data. In practice, it is accepted that pathology raw data is not established until the anatomic pathology report is signed, which includes finalized histopathology diagnoses. Thus, raw data is only altered if changes are made to a signed report and associated tables. By the FDA GLP final rule (U.S. FDA 1987), raw data is not yet established at the initiation of a contemporaneous peer review but have already been generated at the initiation of a retrospective peer review. This distinction is important in addressing many of the subsequent points in Section 2 of the guidance.

• 2.2. The study plan or subsequent amendments should provide an appropriate level of information to allow reconstruction of how tissues will be selected for peer review whilst allowing sufficient flexibility to react to unexpected pathology findings.

While the manner in which tissues are selected for peer review could be detailed within the protocol, the more common and acceptable practice is to detail the tissue selection process in a peer review SOP. Minimum recommendations on what should be reviewed as part of the peer review have been previously published (Morton et al. 2010). The peer review process should allow for flexibility, such as the evaluation of additional slides and other study data, to ensure that all potential target tissues are thoroughly evaluated and all compound-related findings (expected or unexpected) are properly identified, at least down to a no-effect level if possible. In essence, the peer review pathologist needs to have the latitude to be able to increase the scope of the review as the peer review unfolds in order to fulfill these objectives. The materials and methods, including a list of tissues that were evaluated as part of the peer review, are documented within the peer review memo, which is prepared, signed, and dated by the peer review pathologist.

• 2.3. If the pathologist who is appointed to perform the peer review is located at a site geographically remote from the site where the study was performed there is no requirement for them to be formally appointed as a principle investigator. Because the reviewing pathologist is interpreting data and not generating data it would be appropriate for them to be considered as a contributing scientist. The study director maintains ultimate responsibility for ensuring that the peer review process is conducted in accordance with the principles of GLP (see bullets 3.1-3.3).

As stated in the OECD guidance, the peer review pathologist is not a principal investigator as he or she is neither generating raw data nor contributing as an author to the final report. The peer review pathologist, as an important scientist contributing to the overall study, does need to be identified in the study protocol, amendments, and/or in study documentation. Other pathology evaluations such as retrospective peer reviews, consultant reviews, or specialist reviews that may result in new data should also be documented in the study protocol or amendments. Study pathologists are responsible for the interpretation of pathology study data and for placing these data into context so that, in collaboration with the study director, conclusions for the study are drawn.

• 2.4. Details of how the peer review was conducted should be documented and retained within the study file. These activities will include information on the identity of the tissues that were reviewed when the tissues were reviewed and by whom. Notes made by the peer review pathologist which are used to record observations during the histopathological examination of individual slides do not normally have to be retained in the study file.

The conduct of the peer review should be documented in the form of a peer review memo, which is signed and dated by the peer review pathologist. The memo should list the tissues and any other data reviewed, peer reviewer name, and a clear declaration if the peer review pathologist agrees with the overall interpretation in the pathology report. The date on the signed peer review memo indicates the peer review process has been concluded, to include completion of the tissue and data review. Since the memo does not contain raw data, retention in the study file with appropriate archival is adequate; however, some facilities prefer to also include it in the study report.

There is no requirement to retain any peer review notes or minutes of discussions regarding preliminary histopathologic diagnoses or interpretation between the peer review pathologist and study pathologist in the study file. This pertains to preliminary diagnoses, worksheets, draft versions of the study pathologist’s interpretation/narrative (created or annotated by the peer review pathologist or study pathologist), and any records of changes made to the preliminary microscopic findings and draft study report as a result of the peer review. The study pathologist has the sole responsibility and ownership for finalizing histopathology diagnoses and final interpretation in the narrative as indicated by his or her signature on the anatomic pathology report. Notes and drafts are not essential for the reconstruction and evaluation of the pathology section of the final study report and are not considered raw data and thus do not require an audit trail or retention after the pathology report is finalized (Morton et al. 2010; U.S. FDA 1987).

• 2.5. All correspondence regarding the histopathological evaluation of the slides used for peer review between the sponsor and representatives of the test facility and the peer review pathologist should be retained in the study file, including minutes of teleconferences between the sponsor and the test facility.

The essential correspondence to retain are the particular communications that reflect the processes, plans, and expectations directly linked to the slides used in the peer review, especially those that are not captured in other study communications. Examples may include correspondence on the process involved in the selection of the slides for review, the selection of animals for full slide review, and the review of additional potential target tissues. This guidance statement should not be interpreted to mean that “all” correspondence needs to be retained. Communications regarding preliminary observations (pathology diagnoses that are not locked or signed) and draft pathology interpretations would not be required to be maintained since these are pathology working notes.

• 2.6. For the purpose of reconstruction, raw data is defined as the documentation described in bullet 2.4 and 2.5. The original histology slides that are assessed by the reviewing pathologist are derived from the test system and meet the definition of specimens. However, the slides and corresponding blocks are needed for the reconstruction of the histopathology portion of the study and consequently must be archived for the same duration as the raw data.

It is important to note that the OECD guidance is consistent with the FDA and Japanese Ministry of Health, Labour, and Welfare (Japanese MHLW) in its consideration of slides and blocks as specimens (U.S. FDA 1987; Japanese MHW 1997) and not raw data.

For contemporaneous peer reviews, the documentation addressed in bullet point 2.4 (peer review memo) or 2.5 (communication regarding the activities in the peer review between the sponsor and representatives of the test facility and the peer review pathologist) are not considered raw data but are documents that help define study-related activities. This documentation is important to allow for reconstruction of the process and should be maintained in the study file and archived, but they are not needed for reconstruction of the raw data (finalized pathology report), which is an important distinction.

In a retrospective peer review, the raw data has been generated (the finalized pathology report) and may be amended if there are significant differences of opinion in the interpretation. The term “significant” in this context is not related to statistics but refers to a meaningful or impactful difference in the histopathologic diagnosis and/or interpretation. In general, examples of significant differences in the diagnoses and/or interpretation might include those that would change the no observed effect level (NOEL), no observed adverse effect level (NOAEL), and/or target tissues with test article effects. Since the raw data has been generated, it is appropriate to maintain the pathology table changes and versions of signed reports as recommended in the guidance, allowing for a full reconstruction of the process and maintaining transparency. Interim notes taken by the peer review pathologist would not need to be maintained (Morton et al. 2010; U.S. FDA 1987).

• 2.7. If the peer reviewing pathologist does not concur with all or some of the conclusions drawn by the original pathologist a clear, transparent and unbiased process should be implemented to resolve their differences. This process should be documented within the facility’s SOPs or procedures.

In most instances, at the completion of a contemporaneous or retrospective peer review, there will be consensus on the overall pathology findings and interpretation as the study pathologist and the peer review pathologist would have had the opportunity to resolve differences so that the final pathology report (or amended pathology report) reflects such consensus. As the guidance indicates, if consensus on important issues is not achieved, additional processes to resolve differences should be defined in SOPs and/or protocol amendments. Examples of SOP and/or protocol wording might be “Differences of opinion may be resolved through consultation with other pathologists and/or subject matter experts or by convening a pathology working group (PWG).” Details on the recommended methodology for a PWG are described in OECD guideline no.116 and have been previously published (Mann and Hardisty 2013; Morton et al. 2010).

• 2.8. Where the peer reviewing pathologist’s findings were significantly different from the original interpretation of the study pathologist, a description of how differences of interpretation were handled and changes made to the study pathologist’s original interpretation should be discussed in the final report.

In accordance with the 1987 FDA GLP final rule (U.S. FDA 1987), only the finalized pathology report represents raw data. So the study pathologist’s “original interpretation” is the point of creation of the microscopic pathology raw data, which is when the pathology report is finalized. At initiation of the contemporaneous peer review, the original interpretation of the study pathologist (finalization of the pathology report) has not yet been generated and, thus, there would be no changes to discuss as only the consensus interpretation and diagnoses would be presented in the final report. In a retrospective peer review, all changes to the original interpretation (finalized pathology report), whether they be minor or significant, should be documented in an audit trail and must be captured and discussed in a report amendment covering all affected aspects of the study report.

• 2.9. If, despite following procedures designed to resolve any differences of opinion, agreement cannot be reached then an independent expert or panel of experts may be used to resolve the issue. The conclusions of the panel should be clearly documented in the final report.

If the study pathologist and peer review pathologist cannot reach agreement through discussions and consultations in either a contemporaneous or retrospective peer review, possible processes for resolution include a PWG or mediation by a subject matter expert of the particular issue (Morton et al. 2010; OECD 2014b). A PWG associated with a retrospective peer review generally produces a separate report that supersedes the relevant portions of a pathology report (not necessarily the entire report) as a PWG usually is convened for a specific issue. Using a PWG linked to a contemporaneous peer review should be captured in a protocol amendment or the peer review memo. The PWG process details should be covered in an SOP and/or a protocol amendment.

• 2.10. In most cases where there are no significant differences of opinion it will not be necessary to report in detail the outcome of the peer review in the pathology report or the final report. A simple statement that it was conducted and that the pathology report presents the agreed findings would usually suffice.

The simple statement that the peer review pathologist agrees with the study pathologist’s interpretation should be contained within the peer review memo as discussed in sections 2.1 and 2.4.

• 2.11. There is no requirement for the peer reviewing pathologist to sign the pathology report or the final report. However, in the absence of a signature there is an expectation that the peer reviewing pathologist will sign the statement described in section 2.10. This statement should be retained in the study file.

Signing of a peer review memo by the peer review pathologist is consistent with recommended practices (Morton et al. 2010). The signed and dated pathology report documents the final interpretation of the study pathologist, and the signed peer review memo indicates the peer review pathologist’s agreement. The peer review memo is generally signed and dated after the pathology report is finalized.

• 2.12. The identity and affiliation of the peer reviewing pathologist should be listed in the final report.

This information can be included in the relevant section(s) of the anatomic pathology and/or study report (contemporaneous peer review) or amended anatomic pathology and/or study report (retrospective peer review). If the peer review memo with identity and affiliation of the peer review pathologist is included in the final report, further listing of this information is not necessary but can be included.

Section 3. GLP Compliance of Peer Review

• 3.1. The peer review process can lead to changes in the interpretation of histopathology findings that in turn may influence the outcome and conclusion of the study. Consequently, there is an expectation that the peer review should be conducted in compliance with GLP. However, it is recognised that for the peer review to be of scientific value it has to be conducted by a person with the appropriate specialist experience and expertise; consequently that may necessitate the use of acknowledged experts in particular fields who do not work within a GLP test facility. When a decision is made to perform pathology peer review in a non GLP facility it should be justified and recorded within the study plan and final report. Alternatively consideration should be given to whether it would be more appropriate for the pathologist who conducts the peer review to perform their review at the test facility that conducted the study. This would remove the need to transfer histopathology slides from one site to another and would also allow the peer reviewing pathologist to perform their work under the umbrella of an established GLP quality system. In such circumstances there is an expectation that the peer reviewing pathologist would receive an appropriate level of training in the relevant facility procedures.

It is important to provide some clarification regarding the statement, “When a decision is made to perform pathology peer review in a non GLP facility it should be justified and recorded within the protocol and final report.” This information, if available, should be included in the protocol and in the final anatomic pathology and/or study report. If a peer review is to be conducted in a non-GLP-compliant facility, the GLP status of the peer review should be noted in the compliance statement of the anatomic pathology and/or toxicology report. When an external peer review pathologist is identified after the protocol is issued, the protocol can be updated by amendment with the newly assigned peer review pathologist’s information. If a peer review is conducted in a GLP facility and the pathologist has appropriate training relevant to peer review, the peer review should be considered GLP compliant if the applicable peer review SOPs are followed, and additional formal training at the relevant facility should be unnecessary. In those instances when a peer review is conducted at the GLP study test facility by an external peer review pathologist who does not have prior relevant GLP training and SOPs to follow, he or she can undergo relevant training and use the relevant SOPs to make the peer review GLP compliant.

• 3.2. The study director will be making a statement concerning the extent to which their study complies with GLP. If electing to utilise a non-GLP organisation for peer review the study director needs to be satisfied that the peer review process is sufficiently well managed, and that peer review data is of adequate quality. Key elements to consider include, but are not necessarily limited to:

• 3.2.2. A review of the facility’s SOPs or a documented agreement that the peer reviewing pathologist will use the test facilities SOPs and procedures.

• 3.2.3. Chain of custody of samples and associated paperwork.

• 3.2.4. Security of samples and documents whilst at the peer reviewing pathologists facility

• 3.2.5. Validation of any computer applications (if applicable).

• 3.2.6. Adequate quality assurance activities which may include an audit of the premises and equipment used by the reviewing pathologist.

These considerations by the study director are in accordance with the study director’s responsibilities described in the 1987 FDA GLP final rule (U.S. FDA 1987). The peer review pathologist is verifying the accuracy of the pathology diagnoses and interpretations and is not generating data, as this can only be done by the study pathologist. The study pathologist is ultimately responsible for the interpretation of pathology study data and for placing these data into context for the study report. Since the OECD considers the peer review pathologist a scientist who does not have responsibility for primary generation or interpretation of data and thus is not a principal investigator, quality assurance inspections and compliance statements generally should not be required if the study director is satisfied with the peer review methods and procedures.

• 3.3. If the peer review has been conducted in a non-GLP facility then this should be documented within the study director’s statement.

This section is consistent with the study director’s responsibilities (U.S. FDA 1987) and is previously referred to in section 3.1 in regard to making a note in the compliance statement.

Section 4. Summary of Expectations

4.1. Peer review of histopathology is an important part of the process which ensures the quality of the interpretation of study results and can have a significant impact on the study outcome. It is therefore essential that peer review procedures are planned, conducted, documented and reported such that the integrity of the regulatory study is not compromised and activities can be fully reconstructed and verified.

4.1.1. Histopathology peer review activities should be described within the study plan or subsequent amendments.

The peer review should be a protocol- or protocol amendment–directed activity. The detailed methods for conducting a peer review need not be included in the protocol if they are documented in an SOP. Peer review procedures and methods need to allow sufficient flexibility for the review of additional materials when needed, to fully achieve the peer review objectives.

4.1.2. Documentation of the peer review should describe the tissues and documents examined by the peer review pathologist. Reporting of the peer review should be sufficiently detailed to allow reconstruction of the process and of the opinions expressed.

Tissues and documents examined during the peer review should be described and documented in the peer review memo. All changes associated with a retrospective peer review are documented in an audit trail and clearly reported in order to reconstruct the process and opinions expressed. In contemporaneous peer reviews, the protocol, relevant amendments, and peer review memo provide adequate documentation so as to achieve consensus during the peer review process. The study pathologist is responsible for finalizing histopathology diagnoses and providing the final interpretation.

4.1.3. There should be documented procedures that describe how any differences of opinion will be resolved.

A documented process such as an SOP or protocol amendment should be in place for addressing unresolved differences where consensus is not reached within the normal peer review process.

4.1.4. Any differences of interpretation that result in a significant change of the study pathologist’s original interpretation should be discussed in the final report.

At the time of a contemporaneous peer review, the report narrative and diagnoses are generally in draft form and can be updated by the study pathologist. Therefore, changes made to the draft report narrative and diagnoses by the study pathologist as a consequence of peer review are not documented in the final report. Only the final interpretations of pathology diagnoses are presented in the final report. All changes to finalized diagnoses and interpretations in a retrospective peer review should be subject to an audit trail and must be captured and discussed in an anatomic pathology report amendment.

4.1.5. The identity and affiliation of the peer reviewing pathologist should be clearly stated in the final report.

This is consistent with common practices for pathology peer review. This information should be included in the relevant section(s) and/or by inclusion of a peer review memo into the anatomic pathology and/or study report or amended anatomic pathology and/or study report.

Summary

Peer review is a critical and essential component of the histopathology reporting process in regulatory studies. The peer review process should be adaptive and evolve as necessary to provide the most accurate diagnoses and interpretation. However, key features of the practice of peer review that should not change include the flexibility to meet changing needs and unique study requirements, ability for the peer review pathologist to explore all possible evidence of toxicity within a nonclinical toxicity study, and the direct interaction of the peer review pathologist working in close collaboration with the study pathologist in an effort to verify the accuracy of the pathology diagnoses and interpretations. Any changes to the pathology peer review process should facilitate these key features.

OECD guidance no. 16, an advisory document, provides valuable guidance on how the peer review of histopathology should be planned, managed, documented, and reported in order to meet GLP expectations and requirements. This review represents the consensus view of the global societies of toxicologic pathology on interpretation of the guidance.