Interactive effects of psychosocial stressors and gender on mouse mammary tumor growth

We have previously demonstrated that social housing condition significantly affects the growth rate of the androgen-responsive Shionogi mouse mammary carcinoma (AR SC115) in male mice. The present study examined the effects o f social housing condition and acute daily exposure to a novel environment on the growth rate of an androgen-independent variant of the AR SC115 carci noma, designated SC115V, in male and female mice. Immediately following tum or cell injection, male and female mice that were reared as individuals (I) or in groups (G) of the same sex were rehoused either from individual to s ame-sex groups (IG) or from group to individual (GI), or remained in their group housing condition (GG). Approximately half the mice in each housing c ondition were subjected to acute daily exposure to novel environments (nove lty stress), a treatment shown previously to increase the significant diffe rence in tumor growth rates between male mice in the IG and GI housing cond itions. The remaining mice were left undisturbed (no novelty stress). In th e presence of acute daily novelty stress, the growth rate of the SC115V tum or was significantly increased in GI compared to IG males. However, no sign ificant differences in SC115V tumor growth rates among nonstressed GI, IG, or GG males were observed. For females, in contrast to males, acute daily n ovelty stress significantly decreased tumor growth in GI compared to IG mic e, whereas under nonstressed conditions, tumor growth rate was significantl y increased in GI compared to IG females. Neither housing condition nor nov elty stress altered estrous cyclicity, nor did the stage of the estrous cyc le at the time of tumor cell injection influence tumor growth rates. These findings suggest that social housing condition and novelty stress may inter act to produce differential effects on the growth rate of the SC115V tumor in male and female mice. (C) 1999 Elsevier Science Inc.