Introduction Hereditary breast cancer accounts for 5% to 10% of all cases and the most frequently found germline mutation occur in tumour suppressor gene BRCA.

Methods To estimate the incidence of individuals with a high probability of carrying a mutation in BRCA1 or BRCA2 genes, a questionnaire with 13 questions was developed to screen individuals at a high risk of hereditary cancer among breast cancer patients at the National Cancer Institute of Brazil. This instrument was based on the criteria used by the National Comprehensive Cancer Network for the referral of patients with breast cancer for genetic counselling. Patients who answered yes to any of the questions were interviewed about their family history. The probability of BRCA gene mutation was determined by the statistical model BRCAPRO.

Results Among 118 patients who were interviewed with the screening questionnaire, 52 (44.1%) answered yes to at least one question. Using a >10% BRCA gene mutation probability threshold, 4.4% of breast cancer patients had a high risk of being carriers of a germline mutation of BRCA1 or BRCA2 genes. The greater the number of affirmative answers, the more likely the patient had a mutation (r=0.621; p<0.001).

Conclusion A screening tool can easily identify which patients should be referred for genetic counselling. The use of probability models can assist in building and adapting these questionnaires.