ArticleInternational journal of cancer2026
Age at First Pregnancy, Adult Weight Gain and Postmenopausal Breast Cancer Risk: The PROCAS Study (United Kingdom).
Article in International journal of cancer, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 1 paper.
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1 citing paper in PubMed.
- Identification and management of genetic susceptibility to cancer: UK perspective.BMJ oncology · 2026Review
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8 authors.
Funding
Abstract
Adult weight gain (AWG) increases postmenopausal breast cancer risk, whereas an early first pregnancy (FP) is protective. As pregnancy is a key contributor to weight gain, we investigated a potential interaction effect between these two factors on BC risk. We analysed prospective data from 48,417 women in the Predicting Risk of Breast Cancer at Screening (PROCAS) cohort (recruited 2009-2015). A Cox proportional hazards model was used to test for an interaction between first pregnancy age and weight gain on breast cancer risk. After a median follow-up of 6.4 years, 1702 incident breast cancers were identified. Compared to women with an early FP (< 30 years) and stable weight (≤ 5%), risk was highest among those with substantial AWG (> 30%) combined with a late FP (≥ 30 years) (HR: 2.48, 95% CI: 1.82-3.37) or nulliparity (HR: 2.38, 95% CI: 1.74-3.27). Elevated risk was observed even with moderate weight gain (5%-15%). A non-significant positive trend toward an additive interaction was observed for late FP (Relative Excess Risk due to Interaction (RERI): 0.32), whereas the risk in nulliparous women appeared independent of weight gain (RERI: -0.05). Maintaining a stable adult weight and an early first pregnancy are independently associated with a lower breast cancer risk. However, adult weight gain remains a significant risk factor regardless of reproductive history. The combination of high weight gain and late or no pregnancy identifies a high-risk group who could be prioritized for weight-management interventions in cancer prevention settings.
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