Multiple sclerosis and breast cancer.

Multiple sclerosis (MS) and breast cancer (BC) share common features; most notably, both are more frequent in women than in men. In addition to the involvement of sex hormones, a number of genetic and pharmacological studies support a possible relationship between these two diseases. However, there are no conclusive epidemiological findings related to MS and BC worldwide, and there are no recent data for the US population. We conducted a case-control study using a hospital inpatient discharge dataset (21,536 cases and two control series totaling 59,581 controls) from the Texas Health Care Information Collection. We assessed occurrence of MS in BC cases and in two control series: diabetes mellitus type II, and open wounds. After controlling for age, race-ethnicity, and health insurance status, a statistically-significant protective association was detected: BC cases were 45% less likely than diabetic controls to have MS (OR=0.55, 95% CI=0.37-0.81), and 63% less likely than open wound controls to have MS (OR=0.37, 95% CI=0.21-0.66). Our study presented here is the only current assessment of the association between MS and BC in the USA and suggests a protective effect of MS on BC in the hospitalized population.