Tumors of the mammary glands are predominantly malignant and highly metastatic in nature. Surgery is the primary treatment performed for this condition though adjuvant chemotherapy is suggested to increase survival time (ST) in cats.
One currently used regimen is radical surgery plus doxorubicin adjuvant chemotherapy which has a median ST and median disease-free interval (DFI) of 448 and 255 days, respectively. Median ST for surgery alone is only 10-14 months. In humans, mitoxantrone is used for treatment of neoplastic disease in situations where the patient cannot tolerate the toxicity and adverse effects of doxorubicin. Since doxorubicin’s adverse effects in cats are primarily anorexia and kidney injury, there is a need to find another chemotherapeutic agent in its place. This study’s aim was to investigate the disease-free interval, survival time and adverse effects of using radical mastectomy and adjuvant mitoxantrone as a combined therapy in cats with malignant mammary tumors.
Twelve cats met the study’s inclusion criteria. Following histopathology, each cat was staged according to the World Health Organization’s staging system. Surgery involved removing the mammary chain containing the tumors where a 3 cm margin was obtained around the tumors. Mitoxantrone was started 15-30 days after surgery (6mg/m2 IV every 21 days for four cycles) with the goal of delaying metastasis. Of the twelve cat cases, three were intact, one cat was early spayed (<1 year of age), four cats were late spayed (> 1 year of age or of unknown age). Six cats were stage l and six cats were stage III.
The results of this study indicated the overall median DFI was 360 days and median ST was 480 days. The most frequent adverse events of mitoxantrone chemotherapy were azotemia (n=5), anorexia (n=4), leukopenia (n=3) and vomiting (n=1). Anorexia and vomiting started within 1-5 days after administration and did resolve after supportive treatment. Due to development of azotemia, it was recommended that kidney function should be monitored carefully during and after completion of mitoxantrone chemotherapy. (VT)