It has always been assumed that chemotherapy is immunosuppressive. This study was done to evaluate the effects of 2 common chemotherapy protocols on T- and B-cell numbers and humoral responses to de novo vaccination in dogs with cancer. Twelve dogs with lymphoma and 9 dogs with osteosarcoma were included. Doxorubicin at 30 mg/m2 was used as single-agent therapy in 12 dogs for a total of 5 treatments administered over a 15-week period. Dogs receiving the multidrug chemotherapy protocol for lymphoma received cyclophosphamide, vincristine, prednisone, doxorubicin, and L-asparaginase (CHOP) according to a previously described protocol. Healthy, age-matched dogs were used as controls. Before treatment, dogs with cancer had significantly fewer CD4+ T cells and CD8+ T cells than did healthy dogs. Doxorubicin treatment did not cause a significant decrease in T- or B-cells. Treatment with the CHOP protocol caused a significant and persistent decrease in B-cell numbers. Response to vaccination (antibody titers) was not significantly different between control and chemotherapy-treated dogs. Although the sample size is small, the results of this study suggest that chemotherapy is not immunosuppressive in all cases.

COMMENTARY: More and more owners are choosing to treat cancer in their pets. Knowing what to expect is helpful in making that decision. This article describes a surprising finding that immunosuppression is not guaranteed to be a side effect of treatment, and the patients in this study responded adequately to vaccination.

Effects of chemotherapy on immune responses in dogs with cancer. Walter CU, Biller BJ, Lana SE, et al. J VET INTERN MED 20:342-347, 2006.