Association between breast cancer and hepatitis C: A joint study of hospitalized patients and nationwide cohorts.

Whether hepatitis C virus (HCV) infection is associated with breast cancer risk remains elusive, and we aimed to elucidate it. A nationwide population-based cohort study of the Taiwan National Health Insurance Research Database (TNHIRD) was conducted. Additionally, breast cancer risk factors, and HCV core expression were surveyed in breast cancer patients of a tertiary care center. Three TNHIRD cohorts (1:4:4, propensity score-matched, 2003-2012), including HCV-treated (3646 HCV-infected females with interferon-based therapy ≥6 months), HCV-untreated (n = 14,584) and HCV-uninfected (n = 14,584) cohorts, were enrolled. The HCV-untreated cohort had the highest 9-year breast cancer cumulative incidence (2.017%; 95% confidence interval [CI]: 1.382%-2.846%), while the HCV-treated (1.073%; 0.414%-2.356%), and HCV-uninfected (1.453%; 0.785%-2.486%) cohorts showed no difference. Untreated HCV infection (hazard ratio [HR]: 1.701; 95% CI: 1.205%-2.400), urban residency (1.658, 1.183-2.323), and baseline cardiovascular events (1.920; 1.005-3.668) were associated with incident breast cancers. The interaction analysis showed that particularly among patients <49 years, HCV infection was associated with breast cancer development (2.193; 1.097-4.384). Of 12,170 hospitalized breast cancer patients, 4.90% were HCV Ab-positive. HCV Ab-positive patients were older (60.92+/-10.82 vs 53.91+/-11.38 years, P < 0.0001) and had a higher body mass index (25.39+/-5.1 vs 24.5+/-4.3 kg/m2, P = 0.007), rates of diabetes (30.60 vs 19.98%, P < 0.0001), hypertension (46.9 vs 30.39%, P < 0.0001), dyslipidemia (25.52 vs 20.28%, P = 0.031), and hyperuricemia (11.38 vs 5.52%, P < 0.0001) than their counterparts. No HCV core-positive cells were demonstrated in breast cancer tissues. Conclusions: Untreated HCV infection, urbanization, and cardiovascular events were potential risk factors for breast cancer. The HCV-associated risk was most prominent among patients <49 years, might not be associated with in situ HCV core-related oncogenesis but with metabolic alterations, and was reversed by anti-HCV therapy.