CD8A and breast cancer: This immune suppressive microenvironment seemed to be transient, as the immune milieu resembled the nulliparous state 6 weeks' postweaning.46 Low CD8+ T cell infiltration in the postpartum microenvironment resulted in tumor cell escape from immune surveillance and was also associated with decreased survival rates.35 44 As both immunosuppressive and immune-tolerant programs are enhanced during involution, they could be important mechanisms for mammary tumor promotion.