Chemo for Mammary Cancer

The therapy may prolong life in affected cats

Feline mammary cancer (FMC) is aggressive. About 90% of cases are malignant, with metastasis already present at the time of diagnosis. The risk is highest for intact female cats and cats who have had heat cycles before being spayed. A recent study from Portugal looked at cases of cats with metastatic mammary cancer from a group of veterinary hospitals to investigate the progression of FMC with or without adjuvant treatment. The study evaluated 73 cats verified via histopathology to have mammary adenocarcinoma with metastasis. The metastatic spread was confirmed, and 75% of the cats had surgery to remove as much of the cancer as possible.

The cats were divided into three groups based on the therapy elected: those receiving maximal tolerated dose chemotherapy with doxorubicin or carboplatin; those receiving metronomic chemotherapy with chlorambucil or cyclophosphamide; and those receiving toceranib phosphate.

At a six-month check, 19.4% of the cats were alive, with no significant difference seen in the survival rate or progression of the cancer in the different treatment groups. The presence of a pleural effusion (fluid in the chest cavity) was a negative prognostic factor. The fluid was attributed to metastases to the lungs and chest. Cats with pleural effusion only lived 16 days past the start of therapy. Cats without pleural effusion lived for 64 days on average.

While these results may sound depressing, 20% of the cats, all of which had advanced disease when treatment began, were alive after six months. If they had been diagnosed earlier, treatment may have been more effective. “To the best of our knowledge,” wrote the authors, “this study includes the highest number of patients with metastatic FMC assessed. Despite the overall poor prognosis, some cats survived more than six months, indicating that adjuvant treatment may be an option to consider in metastatic disease.”

The results indicate that chemotherapy may prolong life in some cats with mammary cancer with metastasis. If the cats had been diagnosed earlier, treatment may have been more effective. With any cancer, early diagnosis is key. If you notice a lump on your cat, get her to your veterinarian immediately for an examination. See “Mammary Cancer Often Spreads” at or in our March 2019 issue.n

Petrucci G, 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.