CXCR4 and breast cancer: In unadjusted exact conditional regression analysis of 20 variables (Table S1), breast cancer was marginally inversely associated with CXCR4-tropic HIV (Odds Ratio (OR) = 0.20, 95% confidence interval (CI) 0.02–1.1) as well as menopause (OR = 0.13, 95% CI 0.003–1.0), defined as not having a menstrual period for one year or more.