Women with neurofibromatosis 1 are at a moderately increased risk of developing breast cancer and should be considered for early screening.

Background: Malignancy risks in patients with neurofibromatosis 1 (NF1) are increased, but those occurring outside of the nervous system have not been clearly defined.

Aim: To evaluate the risk of breast cancer in women with NF1 in a population-based study.

Methods: The risk of breast cancer in a cohort of 304 women with NF1 aged >or=20 years was assessed and compared with population risks over the period 1975-2005 using a person-years-at-risk analysis.

Results: There were 14 cases of breast cancers in the follow-up period, yielding a standardised incidence ratio (SIR) of 3.5 (95% CI 1.9 to 5.9). However, six breast cancers occurred in women in their 40s, and the SIR of breast cancer in women aged <50 years was 4.9 (95% CI 2.4 to 8.8).

Interpretation: Women with NF1 aged <50 years have a fivefold risk of breast cancer, are in the moderate risk category and should be considered for mammography from 40 years of age.