Fraction of cancers attributable to and prevented by reproductive factors and exogenous hormones use in Italy

Objective: Endogenous and exogenous hormonal factors have been associated with female breast, genital, and colorectal cancer risk. The aim of the present study is to conduct an evidence-based evaluation of the fraction of cancers attributable to and prevented by exogenous hormonal (i.e., combined oral contraceptives [COC] and combined estrogen-progestogen menopausal therapy [CEPMT]) and reproductive factors (i.e., parity and breastfeeding) in Italy. Study design: We calculated the population attributable and prevented fractions combining relative risks and prevalence of exposure in Italian women. Italian cancer incidence and mortality data were extracted from national sources and used to estimate the number of cancer cases and deaths attributable to reproductive factors and exogenous hormones in Italy in 2020. For long-term effects, a 20-year latency period was considered. Results: COC were responsible for 4.4 % of breast and 10.9 % of cervical cancers in women aged 15-44, but also avoided 6.4 % of endometrial, 5.6 % of ovarian, and 2.9 % of colorectal cancers in women of all ages. Overall, COC use prevented 1174 cancer diagnoses and 577 cancer deaths. CEPMT caused 0.4% of breast cancers at age 45-69. Low parity accounted for 8.1 %, 11.8 % and 15.5 % of breast, endometrial and ovarian cancers, respectively (6267 cases, 1796 deaths). Breastfeeding avoided 6.4 % of breast cancers (3775 cases, 897 deaths). Conclusions: Our analysis quantified the complex effects of hormonal and reproductive factors on cancer burden in Italian women.