Effects of psychosocial stressors on mouse mammary tumor growth

We describe a sensitive and replicable animal model which demonstrates that psychosocial variables both increase and decrease tumor growth rate. The effects of social housing condition and daily exposure to novel environments were investigated in mice bearing the transplantable androgen-responsive Shionogi mouse mammary carcinoma (SC115). Being reared individually housed and remaining individually housed or being reared in a sibling group and then singly housed following tumor cell injection markedly increased tumor growth compared to that in mice remaining in their standard sibling rearing groups (n = 2-3 per group), if animals were also exposed to acute daily novelty stress. In contrast, being reared individually and then moved to a larger social group (n = 4-5 nonsiblings per group) markedly reduced tumor growth, both in the presence and absence of acute daily novelty stress.