In the present study, we demonstrate that social housing conditions significantly alter the response of the transplantable androgen-responsive Shionogi mouse mammary tumor (SC115) to chemotherapy. Mice were reared either in groups (G) or as individuals (I). Immediately following tumor cell or vehicle injection, mice were rehoused from group to individual (GI) or from individual to group (IG) conditions. A combination of Adriamycin (4 mg/kg) and cyclophosphamide (61.5 mg/kg), in a series of three i.p. injections 7 days apart, was initiated when mean tumor weights of mice within a housing condition (GI or IG) reached 1 g. Survival probability was significantly greater in mice in the IG housing condition compared to those in the GI housing condition (47% versus 19%, respectively). Additionally, the median survival time following the initiation of chemotherapy was greater for mice in the IG than for mice in the GI condition (24.5 days versus 15.0 days, respectively). These findings suggest that a psychosocial stressor, social housing condition, can significantly influence chemotherapeutic efficacy.
Supported by a grant from the Medical Research Council of Canada.