NEW STUDY: Doxorubicin Treatment of Mammary Gland Adenocarcinoma in Cats

As you may know, 80-90% of cats with mammary tumours are malignant. Many vets only recommend surgery and recurrence rates are VERY high. In the past, prognoses have been poor. Survival times, up to this point, were short and based on standards established by the World Health Organization and based entirely on the stage of cancer (there are 4 stages).

A recent study from the Animal Medical Center (AMC) in New York calls into question those standard prognostic indicators and provides new hope even in advanced stages of cancer. AMC conducted a retrospective study of 67 cats treated with surgical excision and adjunctive Doxorubicin (chemo drug) and compared it with data from cats who did not receive Doxorubicin. Cats treated with surgery alone, depending on the size of the tumour, had average survival times of 2 years if the tumour was less than 3 cm, but only 4-6 months if the tumour was larger than 3 cm.

AMC found that cats with tumours smaller than 3 cm were 2.4 times more likely to have long term survival than those with larger tumours after surgical excision and Doxorubicin. Doxorubicin increased survival time quite dramatically giving cats a minimum of a year longer than cats that had surgery alone. It increased the average survival time if there was no evidence that the cancer had spread from the previous 2 years to 5-6 years! Quite dramatic indeed. Approximately 60% of cats treated with surgery and Doxorubicin were still alive 3 years later, and 50% were still alive 4 years later. That is pretty amazing considering that many of the cats studied were already older cats (10 or older). They did not have data beyond that point so we do not know if those cats continued to do well for many more years.

They also found that even cats with metastatic disease (meaning the cancer had spread) still had far longer survival times than those cats that did not receive Doxorubicin. If the cancer had spread to the lymph nodes, survival times were as long as 4 years. If it had spread to the lungs, that was decreased, but still averaged 1 year. The increase in survival times when the cancer had spread to the lymph nodes was quite surprising and showed statistics similar to those found in humans in a recent study. It has previously been thought that if the cancer had spread to the lymph nodes, survival would be short.

They also found that radical bilateral mastectomy provided much longer survival times than unilateral or regional mastectomies.

In addition, one other revelation was that even if the cancer was very advanced, surgery and Doxirubicin provided much longer survival times than surgery alone.

The study is:

Doxorubicin Treatment of Mammary Gland Adenocarcinoma in Cats JAAHA 42:110-220, 2006, Novosad CA, Bergman PJ, Obrien MG, et al. The American Medical Center in New York.