Association of surgical approach with complication rate, progression-free survival time, and disease-specific survival time in cats with mammary adenocarcinoma: 107 cases (1991–2014

OBJECTIVE To evaluate potential associations between surgical approach and complication rate, progression-free survival time, and disease-specific survival time in cats with mammary adenocarcinoma. DESIGN Retrospective case series. ANIMALS 107 client-owned cats. PROCEDURES Medical records of cats that underwent surgical excision of mammary adenocarcinoma by means of a unilateral or bilateral (staged or single-session) mastectomy at 9 hospitals between 1991 and 2014 were reviewed. Relevant clinicopathologic data and details of surgical and adjuvant treatments were recorded. Outcome data were obtained, including postoperative complications, progression-free survival time, and disease-specific survival time. RESULTS Complications occurred in 12 of 61 (19.7%) cats treated with unilateral mastectomy, 5 of 14 (35.7%) cats treated with staged bilateral mastectomy, and 13 of 32 (40.6%) cats treated with single-session bilateral mastectomy. Complications were significantly more likely to occur in cats undergoing bilateral versus unilateral mastectomy. Median progression-free survival time was longer for cats treated with bilateral mastectomy (542 days) than for cats treated with unilateral mastectomy (289 days). Significant risk factors for disease progression included unilateral mastectomy, tumor ulceration, lymph node metastasis, and tumors arising in the fourth mammary gland. Significant risk factors for disease-specific death included lymph node metastasis and development of regional or distant metastasis. Among cats that did not develop metastasis, unilateral mastectomy was a significant risk factor for disease-specific death. Treatment with chemotherapy was associated with a significantly decreased risk of disease-specific death. CONCLUSIONS AND CLINICAL RELEVANCE Results supported bilateral mastectomy for the treatment of mammary adenocarcinoma in cats to improve progression-free and disease-specific survival time. Performing bilateral mastectomy in a staged fashion may help to decrease the complication rate.