Journal: International journal of cancer
This prospective analysis from the PROCAS screening cohort (48,417 women; median follow‑up 6.4 years; 1,702 incident breast cancers) examined how adult weight gain and age at first pregnancy jointly influence breast cancer risk.
Key points:
- Reference group: women with early first pregnancy (<30 years) and stable adult weight (≤5% gain).
- Highest risk: women with substantial adult weight gain (>30%) combined with:
- Late first pregnancy (≥30 years): HR 2.48 (95% CI 1.82–3.37)
- Nulliparity: HR 2.38 (95% CI 1.74–3.27)
- Moderate adult weight gain (5–15%): associated with elevated breast cancer risk.
- Additive interaction analysis:
- Late first pregnancy: non‑significant positive trend toward interaction with weight gain (RERI 0.32).
- Nulliparous women: risk appeared independent of weight gain (RERI −0.05).
Clinical implications:
- Lower risk: both maintaining a stable adult weight and having an earlier first pregnancy independently associate with lower breast cancer risk.
- Adult weight gain: a significant risk factor across reproductive histories.
- High‑risk group: women with substantial weight gain plus late or no pregnancy may benefit from targeted weight‑management interventions in breast cancer prevention strategies.