Mammary neoplasia accounts for 17% of feline tumors; most are adenomas or adenocarcinomas. Causes may be related to estrogen and progesterone fluctuations; early spaying can reduce risk for development. Tumors may be discrete and mobile, attached to subjacent tissues, or ulcerated or cystic. Draining lymph nodes may be enlarged. The ratio of malignant to benign tumors is at least 4:1, so any mammary tumor should be considered potentially malignant. Tumor grade cannot be distinguished based on gross appearance; complete staging is recommended, including palpation and aspiration of draining lymph nodes and 3-view chest radiography. Paraneoplastic conditions and retroviral infections are not associated with mammary neoplasia in cats.

Surgical resection is the mainstay of treatment; tumor cells readily spread beyond the primary site, so complete excision should include en bloc resection of the tumor, attached skin and fascia, and associated drainage pathways. Studies mapping lymphatic drainage patterns may be used as guidelines. Adjunctive chemotherapy with doxorubicin or doxorubicin with cyclophosphamide or meloxicam has been evaluated with mixed results. Immunomodulators and small molecule inhibitors are in early phases of investigation. Prognosis is guarded because of high prevalence of local recurrence or metastasis; average time between detection and death is 10–12 months. Prognostic factors for better survival time include smaller tumor size (<3 cm), lower clinical stage, aggressive surgical treatment, favorable histopathological grade, and low mitotic index. Early diagnosis is critical for optimal disease-free interval.

Commentary
As the review mentioned, unanswered questions still exist regarding the risk factors and optimal treatment for this tumor type. Some questions, such as survival benefits of adjuvant chemotherapy, have not yet been fully addressed by existing studies; meanwhile, much of the baseline literature on this disease is several decades old, when fewer cats were spayed and it was more common for masses to be diagnosed later in the course of the disease. This study posed, nonetheless, a useful summary of what we do (or do not) know about how best to address feline mammary masses.—Suzanne Shelly Waltman, DVM, DACVIM (Oncology)

Source
Mammary tumors in the cat: Size matters, so early intervention saves lives. Morris J. J FELINE MED SURG 15:391-400, 2013.