Abstract
Dear Editor:
We read with particular interest the article by Dr Goldschmidt and colleagues 2 entitled “Classification and Grading of Canine Mammary Tumors,” which was published in Veterinary Pathology. It was a very interesting subject since mammary neoplasms are very important tumors in veterinary medicine because they are the most common neoplasms of intact adult female dogs and have high importance in countries in which dogs are not routinely spayed, such as many European and South American countries.
We know that histologic examination of canine mammary gland nodules is the current standard to distinguish benign from malignant epithelial or complex tumors and to classify histologic subtypes, making new data regarding such features such as those provided in Dr Goldschmidt and colleagues’ article very useful. However, there are still some histotypes that are currently recognized in the literature that were not discussed in such article.
The morphologic spectrum of mammary neoplasms in canine species is generally quite different from that seen in humans. However, the increase in reports regarding histologic types of mammary tumors occurring in dogs with a striking similarity with their human counterpart has been raising the interest of veterinary pathologists and clinicians about the possibility of facing distinct subtypes with particular and/or aggressive behavior.
In our diagnostic services, we have frequently observed certain discrepancies between the last World Health Organization histologic classification for canine mammary neoplasms (CMNs) by Misdorp and colleagues, 3 particularly regarding the so-called rare histotypes, which are not discussed. Classifying conventional CNMs such as papillary and tubular types poses no difficulty, as those morphologic variants are widely recognized in both mammary and other epithelial tumors. However, diagnosing rare histotypes that are not commonly discussed in the veterinary literature many times requires knowledge usually gained by systematically evaluating women’s breast neoplasms, which have a more recent histologic classification 4 that discusses some rare histotypes that can be also observed in dogs. Since histologic evaluation is still the main diagnostic criterion for CMNs and is performed before chemotherapy institution, a new histologic classification is highly desirable, particularly because more than 10 years have passed since its publication and many new data regarding CNMs have been documented in the veterinary literature.
Different neoplasms that were not discussed by Misdorp and colleagues’ classification 3 are being more and more published in the veterinary literature, such as micropapillary carcinomas, mammary neoplasms with sebaceous differentiation, lobular carcinomas of the mammary gland, and pleomorphic lobular carcinomas. Important information regarding those tumors were recently published in an useful review. 1 Rare histotypes of CMNs usually have different behavior from the tumors discussed in the Misdorp and colleagues 3 classification, which makes the proposition of a new classification scheme even more important since veterinary pathologists can provide valuable information for practitioners by making a more accurate diagnosis. Given this scenario, a question arises: Isn’t it time to review the canine mammary tumors’ histologic classification?
To address this issue, it is necessary to establish guidelines for the diagnosis of canine mammary tumors. Articles such as the one written by Webster and colleagues 5 are good models. These articles represent a consensus statement in veterinary oncology made by veterinary pathologists and oncologists from around the world and constitute an important basis for producing relevant new material regarding canine mammary tumor classification.
In conclusion, a new histologic classification for canine mammary gland tumors is needed to achieve a standard classification method that has a desirable degree of confidence and that might be applied to a routine diagnostic service, consequently providing to practitioners a better response regarding tumor behavior.