Postoperative adjuvant treatment of invasive malignant mammary gland tumors in dogs with doxorubicin and docetaxel.

BACKGROUND Treatment outcome after surgery alone is unsatisfactory in dogs with invasive malignant mammary gland tumors. HYPOTHESIS Adjuvant doxorubicin or docetaxel will improve the treatment outcome in dogs with high-risk malignant mammary gland tumors, and the use of docetaxel will be feasible in affected dogs. ANIMALS Thirty-one dogs with malignant mammary gland tumors of histologic stages II and III (vascular or lymphatic invasion, regional lymph node metastasis, or distant metastasis) were used. METHODS A prospective clinical trial in which dogs were treated with surgery alone (n = 19) or also received adjuvant chemotherapy (n = 12) with doxorubicin or docetaxel was conducted. Docetaxel was given as an IV infusion at a dose of 30 mg/m2 preceded by dexamethasone and diphenhydramine administration. RESULTS The recurrence-free interval ranged from 13 to 2,585 days (median not reached); the median metastasis-free interval and overall survival were 294 days and 370 days, respectively. Dogs treated with chemotherapy had a tendency toward higher long-term local control and survival rates, but there was no significant difference in the recurrence-free interval (P = .17), time to metastasis (P = .71), and overall survival (P = .12). Factors found to influence the time to metastasis and overall survival included lymph node metastasis (P = .009) and tumor fixation to underlying structures (P = .043, time to metastasis), as well as age (P = .018) and histologic stage (P < .001, survival). Mild allergic skin reactions were the most frequently observed complications of docetaxel treatment. CONCLUSIONS AND CLINICAL IMPORTANCE Chemotherapy did not lead to an improved outcome in this population. Docetaxel treatment was well tolerated. Additional investigations of adjuvant chemotherapy in dogs with high-risk mammary cancer are warranted.