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This is a continuation of Cat Unilateral Mammary Tumor Resection ①.

Histopathological diagnosis
Findings
The right 1st-4th breast tissue submitted showed a 4 x 2.5 x 1.7 cm mass and an enlarged inguinal lymph node measuring 1.7 x 0.9 x 0.4 cm in the 0.4th breast. The mass was transversely excised, and six specimens were prepared, including the long axis margin of the breast tissue and the inguinal lymph node. In the specimen, the breast tissue was the main site of a somewhat unclear breast tumor. The tumor cells were cuboidal to polygonal, forming an irregular tubular papillary to alveolar structure separated by a small amount of connective tissue. The tumor cells had round to oval nuclei with clear central nucleoli and eosinophilic cytoplasm. There was moderate to severe variation in the size of the cells and nuclei, and 6-1 mitotic figures were observed per high-power field. The tumor tissue had infiltrated the surrounding adipose tissue. Vascular invasion was also observed. In the specimen, the tumor was not observed at the resection margin.
The right inguinal lymph node showed a similar tumor growth, which had almost completely replaced the existing tissue structures.

Histopathological evaluation
Breast tumor: Simple adenocarcinoma of the breast, with right inguinal lymph node metastasis

Comment:
A malignant mammary tumor was detected in the submitted mammary tissue. Feline mammary cancer is a tumor that has a high rate of metastasis even after complete resection. In this case, the tumor was not observed at the resection margin, but tumor vascular invasion and lymph node metastasis were observed, so attention should be paid to recurrence and metastasis.
Feline mammary adenocarcinoma is an aggressive malignancy that generally exhibits invasive properties and often metastasizes to regional lymph nodes and distant sites. This type of tumor frequently recurs when resection is incomplete. The incidence of this tumor is higher in intact females compared to ovariectomized females. Unlike canine mammary adenocarcinoma, feline mammary adenocarcinoma usually lacks estrogen receptors. Metastasis occurs in at least 25% of cases, usually initially to the axillary or inguinal lymph nodes and later to distant sites including the lungs and pleura. Recent studies have identified tumor size as an important prognostic factor. In this study, cats with mammary adenocarcinomas less than 3 cm in diameter had a median survival of 21 months, whereas cats with tumors measuring 3 cm or more had a median survival of 12 months.

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