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Metastatic feline mammary cancer

Petrucci G, Henriques J, Gregório H, et al. Metastatic feline mammary cancer: prognostic factors, outcome and comparison of different treatment modalities – a retrospective multicentre study. J Feline Med Surg. October 2020.

Mammary cancer in cats is a common, highly aggressive tumor that requires aggressive therapy to control. It is most common in intact cats or those who experienced heat cycles prior to spaying. Unlike mammary cancer in dogs, over 90% of feline mammary cancer is malignant. The disease is often metastatic at the time of diagnosis, though metastases may be microscopic. Therapy is based on radical mastectomy and potentially chemotherapy. However, a large amount of tumors have already metastasized (generally to the lungs) at the time of diagnosis. The presence of metastatic disease is associated with a very poor prognosis, with reported survival times in the range of 1 month. Several chemotherapeutic protocols have been suggested, however there is little published evidence regarding which therapies are best. The purpose of this study was to investigate the outcome, treatment related toxicity, and prognostic factors in cats with stage IV (metastatic) mammary carcinoma.

The study was designed as a retrospective observational trial recruiting cats presenting to a group of veterinary hospitals from 2012 to 2019. Cats were required to have a complete medical record including a histologic diagnosis of mammary adenocarcinoma, with metastatic disease confirmed based on physical exam (PE), ultrasound, radiographs or CT. Metastasis was confirmed to be adenocarcinoma by FNA or Biopsy when feasible, though several pulmonary masses were diagnosed based on radiography alone.

Cats were divided into three groups based on the therapy elected: those receiving Maximal Tolerated Dose (MTD) chemotherapy with doxorubicin or carboplatin; those receiving metronomic chemotherapy (MC) with chlorambucil or cyclophosphamide; and those receiving toceranib phosphate (TP).

Eighty-four cats were considered, of which 11 were excluded due to incomplete records or lack of confirmation of metastasis, leaving 73 in the final analysis. The median age was 12.3 years (range 6-20) and the predominant breed was DSH. 75% of cats has a previous mammary surgery, while the remainder had distant metastasis at the time of initial diagnosis. 19 cats had received chemotherapy prior to diagnosis of metastasis.

Nine cats (12.3%) received MTD chemotherapy, 15 cats (20.5%) received MC therapy, and 10 cats (13.7%) received TP. The remaining 39 cats (53.4%) did not receive therapy. There were no significant demographic, PE, or bloodwork differences between groups, with the exception that the non-treated cats had a higher proportion of symptomatic animals.

Cats who were asymptomatic at diagnosis had a significantly higher survival time (128 days) compared to those with symptoms of disease (14 days). Specifically, the presence of pleural effusion was a negative prognostic indicator, with cats with pleural effusion living 16 days compared to 64 days without.

Median time to progression was 23 days (0-342 days), and median tumor-specific survival was 44 days. Cumulative survival at 6 months was 19.4%. No significant differences in survival or progression were seen between treatment groups. Examination of Kaplan-Meier curves suggested a lower survival for cats treated with MTD chemotherapy, however this was not significant.

This study had a few limitations. Among these were the retrospective nature and relatively small sample size, especially once stratifying for individual treatment groups. 24.7% of cats had a history of previous oral contraceptive use, which would be unusual in many geographic areas. There was a very diffuse set of histories, with some cats receiving chemotherapy prior to diagnosis of metastasis, which may have contributed to drug resistance. The non-treated animals had more severe clinical signs at diagnosis, which may have led to a reduced survival time in this group. The retrospective nature and lack of blinding means that some bias may have been present, with sicker cats receiving more aggressive chemotherapy.

Overall, this study suggests that there is no difference in survival for metronomic, maximal tolerated dose, or toceranib base chemotherapy in cats with metastatic mammary neoplasia. (MRK)

See also:

Morris J. Mammary tumours in the cat: size matters, so early intervention saves lives. J Feline Med Surg. 2013; 15: 391–400.

Zappulli V, Rasotto R, Caliari D, et al. Prognostic evaluation of feline mammary carcinomas: a review of the literature. Vet Patho.l2015; 52: 46–60.