Early-onset cancer and modifiable risk: quantifying the combined impact of excess body weight and alcohol on breast and colorectal cancer in Italy (18-34 years).

BACKGROUND

Rising rates of cancers diagnosed before the age of 50 have been reported worldwide, including in Italy. Among modifiable risk factors, excess body weight (overweight and obesity) and alcohol consumption independently and synergistically increase the risk of breast and colorectal cancers, including early-onset disease. However, the population-level burden attributable to these exposures among adolescents and young adults (AYA) remains poorly quantified.

METHODS

We combined a targeted overview of the literature with a quantitative Population Attributable Fraction (PAF) analysis to estimate the proportion of early-onset breast and colorectal cancers attributable to overweight/obesity, high-risk alcohol consumption, and their combined exposure in the Italian population aged 18-34 years. Sex- and age-specific prevalence data were derived from the national surveillance system "PASSI", while relative risks were obtained from meta-analyses and large cohort studies, prioritizing estimates from early-onset populations when available. PAFs were estimated using the Bruzzi et al. method, while combined PAFs were calculated assuming independence between exposures. Uncertainty was assessed through Monte Carlo simulations and sensitivity analyses on prevalence and relative risk assumptions.

RESULTS

Among Italian young adults aged 18-34 years, overweight and obesity together accounted for a substantial proportion of early-onset colorectal cancer cases, while high-risk alcohol consumption showed the largest individual attributable fraction. The combined contribution of excess body weight and high-risk alcohol consumption reached 16.6% of early-onset colorectal cancer cases. For early-onset breast cancer in young women, high-risk alcohol consumption was associated with PAFs of 4.6%. Sensitivity analyses confirmed the robustness of the estimates and indicated that uncertainty in relative risk assumptions represented the main source of variability.

CONCLUSIONS

Obesity and alcohol consumption contribute meaningfully to the burden of early-onset breast and colorectal cancers in Italy. Integrating weight management and alcohol risk assessment into clinical practice and public health strategies targeting young adults could prevent a measurable proportion of these cancers and help counteract the rising incidence of malignancies at young ages.