Abstract
Introduction:
Surveillance computed tomography (CT) is performed during the follow-up of patients with lymphoma who have completed initial therapy. However, studies on the clinical benefit of surveillance CT for patients with incurable subtypes, such as follicular lymphoma (FL), are limited. This study aimed to evaluate the value of surveillance CT for patients with FL after achieving the first complete response (CR) or CR unconfirmed in the rituximab era.
Methods:
We retrospectively reviewed the medical records of patients with FL who achieved CR with first-line treatment between 2000 and 2016 at our institution. In patients who experienced first relapse, we examined the patient’s clinical characteristics at the time of relapse, subsequent therapies, and post-relapse survival, based on the method of relapse detection.
Results:
Of the 248 patients who achieved CR after initial therapy, 109 had a relapse, with a median follow-up of 11 years; 100 were enrolled into this study. Relapse was detected by surveillance CT in 61 patients (surveillance CT group) and by means other than surveillance CT, such as the presence of patient-reported symptoms, physical findings, and blood work-up abnormalities (non-surveillance CT group), in 39 patients. There was no significant difference in the patients’ characteristics at the time of relapse between the two groups, except for a higher incidence of extranodal involvement in the non-surveillance CT group. The method of relapse detection did not affect therapeutic selection after relapse and post-relapse survival. In this study, 86.8% of the 38 patients who relapsed with only deep lesions, such as mesenteric or retroperitoneal lymph nodes, had surveillance CT-detected relapse.
Conclusion:
Surveillance CT did not show any clinical benefit for patients with FL in CR; however, it might lead to early detection of relapse in cases of deep lesions that cannot be identified without imaging.
Introduction
Surveillance computed tomography (CT) is a traditional follow-up practice for patients with lymphoma who have achieved the first complete response (CR). The rationale is based on the hypothesis that surveillance CT can detect relapse at an early stage and therefore lead to a favorable clinical outcome. However, previous studies of patients with curable lymphoma subtypes, such as diffuse large B-cell lymphoma (DLBCL) and Hodgkin lymphoma (HL), have reported that routine surveillance imaging with CT or positron emission tomography (PET) detects relapse in only few cases; most relapse cases are detected clinically, based on patient-reported symptoms, abnormal physical findings, and blood workup abnormalities.1–10 Moreover, most previous studies have revealed that surveillance imaging offers no survival benefit for patients with curable lymphoma subtypes, mainly DLBCL and HL.2,5–7,10,11 Given the excessive radiation exposure, medical costs, and unclear survival benefit associated with surveillance imaging, the 2014 Lugano classification discouraged its use for curable lymphoma subtypes, and the American Society of Hematology Choosing Wisely Campaign recommended limiting the use of surveillance CT for curable non-Hodgkin lymphoma (NHL).12,13
Follicular lymphoma (FL) is the second commonest subtype of NHL, accounting for 7–20% of NHL cases.14,15 Since the introduction of rituximab, a chimeric anti-CD20 monoclonal antibody, the prognosis of patients with FL has improved dramatically, with a median survival of >20 years.16,17 However, patients with FL experience incurable relapse after treatment with rituximab-containing regimens.
There are few studies on the clinical benefit of surveillance CT in patients with FL,18–20 compared to studies on DLBCL and HL. These studies have not supported routine surveillance imaging, and the 2014 Lugano classification also describes that judicious use of follow-up scans may be considered in indolent lymphomas with residual intra-abdominal or retroperitoneal disease in the follow-up evaluations section. 12 This study aimed to evaluate the value of surveillance CT for patients with FL after achieving the first CR or CR unconfirmed (CR/CRu) in the rituximab era.
Methods
Patients
We retrospectively reviewed the medical records of patients with FL grades 1–3a, who achieved CR/CRu with first-line treatment between 2000 and 2016 at the National Cancer Center Hospital (NCCH). Patients with disease refractory to first-line treatment and achieved CR after receiving second-line treatment were excluded from this study. The 2008 World Health Organization criteria were used for diagnosis. 21 The International Working Group criteria published in 1999 and subsequently revised in 2007 were used to assess response.22,23 This study was approved by the institutional review board of the NCCH on 13 October 2017, and informed consent was waived because of the retrospective nature of the study. Written informed consent to treatment was obtained from all patients. The reporting of this study conforms to the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement. 24
Follow-up
In accordance with the practice policy at our institution, during each follow-up, patients underwent a symptom assessment, physical examination, and blood workup. Follow-ups were scheduled every 1–3 months during the first 2 years after treatment completion, then every 3–6 months from the third to fifth year, and every 3–12 months thereafter. The blood workup included a complete blood count, serum lactate dehydrogenase, liver function tests, renal function tests, and C-reactive protein; meanwhile, soluble interleukin-2 receptor was not routinely measured. Surveillance CT was generally performed every 6 months for the first 5 years, and then at least once annually. Cervical, thoracic, abdominal, and pelvic CT was used routinely for response assessment and surveillance; however, in the presence of clinical signs giving suspicion of relapse (based on clinical signs), PET-CT was used for confirmation.
Outcome
Patients who relapsed after achieving the first CR/CRu were divided into two groups, based on the method of relapse detection: patients with relapse detected by surveillance CT (surveillance CT group) and those with relapse detected by means other than surveillance CT, such as patient-reported symptoms, abnormal physical findings, and blood workup abnormalities (non-surveillance CT group). The clinical characteristics at relapse and outcome after relapse were evaluated according to the method of relapse detection. Progression of disease within 24 months (POD24) was defined as occurrence of relapse within 24 months after diagnosis. Moreover, patients were categorized into two groups, based on the detected lesions at the time of relapse: the group wherein patients had only impalpable and deep-seated lesions, such as intracranial, intrathoracic, and intraabdominal masses (only deep lesions); and the group wherein patients had at least one palpable and superficial lesion (superficial lesions with or without deep lesions). We examined the relationship between the lesion detected at the time of relapse and relapse detection methods.
Statistical analysis
Categorical data were compared using the chi-square tests. Continuous data were compared using the Welch’s
Results
Patient characteristics at the time of relapse
A total of 248 patients were identified. Five patients died before relapse. The median follow-up duration was 11.0 (range: 1.74–16.0) years. Of those who had relapse (109 patients), nine patients were excluded from the analysis (underwent surveillance PET-CT instead of CT,

Flow diagram of patients in this study.
The most common signs of relapse and patients’ characteristics at the time of relapse are summarized in Tables 1 and 2. The most common sign of relapse was enlarged lymph nodes (
Symptoms at the time of relapse.
CT: computed tomography.
Two patients presented with multiple symptoms at the time of relapse.
Subcutaneous (
Abnormal elevation of lactate dehydrogenase levels and thrombocytopenia (
Characteristics of patients at the time of relapse.
BM: bone marrow; BR: bendamustine and rituximab; CT: computed tomography; DLBCL: diffuse large B-cell lymphoma; ECOG: Eastern Cooperative Oncology Group; FL: follicular lymphoma; FLIPI: follicular lymphoma international prognostic index; GELF: Groupe d’Etude des Lymphomes Folliculaires; HTB: high tumor burden; LDH: lactate dehydrogenase; NA: not applicable; PS: performance status; R-CHOP: rituximab plus cyclophosphamide, doxorubicine, vincristine, and prednisone; R-CMOPP: rituximab plus cyclophosphamide, vincristine, procarbazine, and prednisone; R-CVP: rituximab plus cyclophosphamide, vincristine, and prednisone; RT: radiation therapy; ULN: upper limit normal.
BM biopsy was performed at the time of relapse for 56 patients.
Biopsy was performed immediately at the time of relapse for 36 patients (16 in surveillance CT group and 20 in non-surveillance CT group).
Clinical transformation was suspected in 15 patients. Eight of those patients were pathologically diagnosed with DLBCL. The biopsy results of three of those patients indicated no transformation.
Sixty-seven patients received R-CHOP, 6 R-CMOPP, 4 R-CHOP + R-maintenance, 2 R-CVP, 2 R-CHOP + RT, 3 R-monotherapy, and 1 BR.
Outcome after relapse
There was no significant difference in OS after relapse between surveillance CT group (OS at 10 years: 70.5%; 95% confidence interval (CI), 37.6–88.2%) and non-surveillance CT group (OS at 10 years: 81.5%; 95% CI, 59.1–92.4%;

Overall survival after relapse in patients with follicular lymphoma detected by surveillance computed tomography (CT) and means other than surveillance CT.
According to the attending physician’s discretion, 49 (80.3%) patients in surveillance CT group and 32 (82.1%) in non-surveillance CT group received the next anti-lymphoma treatment, including systemic chemotherapy (24 in surveillance CT group and 12 in non-surveillance CT group), rituximab monotherapy (11 in surveillance CT group and 10 in non-surveillance CT group), ibritumomab tiuxetan (2 in surveillance CT group and 2 in non-surveillance CT group), radiotherapy (RT) only (1 in surveillance CT group), and investigational agents (11 in surveillance CT group and 8 in non-surveillance CT group); there was no significant difference between the two groups (

Time to next treatment from relapse detected by surveillance computed tomography (CT) and means other than surveillance CT: (a) any anti-lymphoma treatment and (b) cytotoxic chemotherapy.
The proportion of patients who received cytotoxic chemotherapy after relapse was 50.8% (
Lesions at relapse
At the time of relapse, 62/100 patients had superficial lesions with/without deep lesions and 38/100 had only deep lesions (intra-abdominal mass,
Relationship between relapse lesions and relapse detection method.
CT, computed tomography.
Superficial lesions include Waldeyer’s ring, cervical lymph node, axillary lymph node, inguinal lymph node, and extranodal mass, which are palpable.
Deep lesions include all lesions that were not superficial.
POD24
POD24 was more prevalent in non-surveillance CT group (13/39, 33.3%) than in surveillance CT group (9/61, 14.8%), although the difference was not significant (
Discussion
As described in the National Comprehensive Cancer Network (NCCN) guidelines, existing data on the clinical benefit of surveillance CT in patients with incurable lymphoma subtypes, such as FL, are limited. 26 This study was a retrospective evaluation of the role of surveillance CT in patients with FL after they achieved the first CR/CRu. Of the 100 enrolled patients, relapse was detected in 61 patients using surveillance CT and in 39 patients using means other than surveillance CT. Follow-up CT was performed strictly, in accordance with our departmental guidelines. There was no significant difference in the OS after relapse between the two groups. Moreover, there was no significant difference in the time from relapse to initiation of the next treatment between the two groups. However, relapse was detected in 33/38 patients with only deep lesions using surveillance CT, and in five using means other than surveillance CT. These results suggest that surveillance CT was not beneficial for patients with FL in CR/CRu; however, it seemed to lead to early relapse detection in patients with deep lesions.
In a similar retrospective study, 78/257 patients who achieved CR after induction therapy relapsed, with a median follow-up duration of 101 months.
18
Of the 78 patients with relapse, it was detected using surveillance CT in only 11 (14%) of them. However, unlike our study, the routine surveillance CT used in this study was only abdominal and/or pelvic CT. Moreover, the interval at which the surveillance CT was performed was not regular. In another study by Goldman
Several studies showed that PET-CT more accurately detected lesions at staging or response evaluation in patients with FL than CT.28–30 Especially, the sensitivity of PET-CT to detect extranodal disease or bone marrow involvement is higher than that of CT. In this study, patients whose relapse was detected by means other than surveillance CT had a higher incidence of extranodal involvement than patients whose relapse was detected by surveillance CT. If surveillance with PET-CT had been performed, then extranodal relapse may have been detected before clinical symptoms appeared. However, PET-CT is not recommended as a standard follow-up modality because of its unclear survival benefit, high false-positive rate, and low cost-effectiveness according to the latest NCCN guideline. 26 PET was not routinely used as an imaging modality for surveillance at our institution; only four patients were followed-up using PET-CT. These patients were excluded from the analysis because they did not undergo surveillance CT.
Goldman
Surveillance CT is considered to contribute to the early detection of deep relapse lesions that could be missed with non-imaging modalities. In our study, of the 38 patients who had only deep relapse lesions, 33 were detected using surveillance CT, and only five were detected by means other than surveillance CT, indicating that the lesions in approximately one-third of the patients with relapse were detected early using surveillance CT. Based on our results, surveillance CT is not associated with clinical outcomes of patients with FL in CR/CRu, but it seems to lead to early relapse detection in patients with deep lesions.
POD24 is a predictor of shorter patient survival in patients with FL, and similar endpoints of early progression after diagnosis or initiation of first-line treatment have also been reported.31–34 However, previous studies did not differentiate the method of progression detection: clinical, radiography, or other means. Bitansky
This study had several limitations. First, it was a retrospective study. Second, the sample sizes of relapse lesion or POD24 analysis were too small to account for the differences in each subgroup. Third, it was difficult to evaluate whether surveillance CT actually had no clinical benefit for patients with CR/CRu because there was no control group (patients followed-up without surveillance CT after achieving the first CR/CRu). Fourth, only patients who achieved the first CR/CRu after the first treatment were enrolled; however, surveillance CT is also performed for patients with FL in partial response or stable disease in clinical practice. Moreover, only one patient was treated with BR (bendamustine plus rituximab); only four patients were treated with rituximab maintenance therapy as initial therapy, and no patient was treated with obinutuzumab, which is the available treatment option for untreated FL; these treatment modalities were recently approved for patients with previously untreated FL in our country. These novel therapies showed a superior progression-free survival (PFS), compared to R-CHOP (rituximab plus cyclophosphamide, doxorubicine, vincristine, and prednisone) in a randomized phase-III trial.35–38 These new treatment strategies prolong PFS even further, which means that more regular surveillance CT is needed to detect one relapse. However, despite these limitations, the strengths of our study lie in the uniform follow-up of the patients with surveillance CT, performed in accordance with our departmental guidelines. Moreover, given the increase in the number of imaging sessions required to detect one relapse following PFS prolongation, surveillance imaging should be performed for selected patients who benefit from it to reduce radiation exposure and health care costs. However, patients undergoing rituximab maintenance therapy may receive additional benefits with the monitoring of active treatment using surveillance imaging. If surveillance imaging detects asymptomatic progression, then toxicity can be reduced by early discontinuation of maintenance therapy. As mentioned, only four patients with rituximab maintenance therapy were included in our study; therefore, further specific studies of the value of surveillance CT for patients undergoing maintenance therapy are required.
In conclusion, our results suggest that surveillance CT is not beneficial to patients with FL in CR/CRu, but it may lead to early relapse detection in patients with deep lesions. Further studies are needed to identify patients with FL for whom surveillance CT is beneficial and to develop an optimal follow-up strategy.
Supplemental Material
sj-tif-1-tah-10.1177_20406207221095963 – Supplemental material for The role of surveillance computed tomography in patients with follicular lymphoma
Supplemental material, sj-tif-1-tah-10.1177_20406207221095963 for The role of surveillance computed tomography in patients with follicular lymphoma by Shunsuke Hatta, Suguru Fukuhara, Takahiro Fujino, Yo Saito, Yuta Ito, Shinichi Makita, Wataru Munakata, Tatsuya Suzuki, Dai Maruyama, Masahiko Kusumoto and Koji Izutsu in Therapeutic Advances in Hematology
Footnotes
Author contribution(s)
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Conflict of interest statement
The authors declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: MK reports grants from Canon Medical Systems.
Availability of data and materials
The data that support the findings of this study are available from the corresponding author upon reasonable request.
Supplemental material
Supplemental material for this article is available online.
References
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