Which reproductive history pattern increases breast cancer risk?

• A. First pregnancy after age 30
• B. Early first pregnancy
• C. Prolonged breastfeeding
• D. Regular lactation cessation near menarche

Answer: (A)

Having a first full-term pregnancy after age 30 increases breast cancer risk because breast tissue remains in a less differentiated, more proliferative state for a longer period. Early pregnancy triggers terminal differentiation of breast cells, making them less susceptible to malignant transformation and reducing lifetime risk. The protective effect is strongest with earlier first birth, and parity generally lowers risk, especially with multiple pregnancies. Breastfeeding also lowers risk through hormonal changes and reduced cumulative estrogen exposure. So late first birth sits in the pattern that raises risk, whereas early first birth and longer breastfeeding are associated with lower risk. The other options describe patterns more aligned with protection or lack of known risk association rather than increased risk.