Associations between Parity, History of Breastfeeding, and T-cell Profile of Ovarian Tumors

Background: Parity and breastfeeding are associated with systemic changes in maternal inflammation and reduced risk of ovarian cancer, but little is known about their impact on the ovarian tumor immune microenvironment.Methods: We evaluated the associations of self-reported parity and history of breastfeeding with tumor-infiltrating T cells among 1,706 ovarian carcinoma cases with tumor tissue collected across four studies. The abundance of tumor-infiltrating T cells was measured by multiplex immunofluorescence in tumor tissue microarrays. ORs and 95% confidence intervals (CI) for the positivity of tumor immune cells were calculated using beta-binomial models and stratified by histotype.Results: Compared with ovarian tumors in nulliparous women, there was no association between parity and ovarian tumor T-cell abundance among all histotypes combined but suggestion of increased cytotoxic T cells and T-cell exhaustion among parous women with clear-cell tumors. When restricted to parous women, history of breastfeeding was associated with increased odds for all T-cell types [i.e., total T, cytotoxic T, helper T (Th), regulatory T, and exhausted T cells], with ORs ranging from 1.11 to 1.42. For every 6 months of breastfeeding, we observed increased odds of activated Th-cell infiltration (CD3+CD4+CD69+; OR, 1.13, 95% CI, 0.99-1.29), with a similar association for high-grade serous tumors, but lower odds in clear-cell tumors (OR, 0.43, 95% CI, 0.21-0.87).Conclusions: History of breastfeeding may alter the ovarian tumor immune microenvironment by modulating the abundance of tumor-infiltrating T cells.Impact: Although replication is required, history of breastfeeding may play a role in the activation of the ovarian tumor immune response.