Breast cancer risk peaks when a patient is in her 40s for BRCA1 mutations and in her 50s for BRCA2 mutations, according to the results of a new study published in JAMA.

Researchers followed nearly 10,000 women with BRCA1 and BRCA2 mutations, including more than 5,000 cancer-free women and more than 4,800 women previously diagnosed with breast or ovarian cancer. They found that 72% of women with BRCA1 mutations will develop breast cancer and 44% will develop ovarian cancer by age 80. For women with BRCA2 mutations, the percentages were 69% and 17%, respectively. For cancers in a second breast, the risk was 41% for BRCA1 mutations and 21% for BRCA2 mutations.

Knowing when their risk is expected to peak will aid patients and providers in making decisions about prophylactic breast or ovary removal. Additionally, the study provided more accurate assessment of cumulative risk than previous studies to date.