Currently, MRI screening for breast cancer in women with a BRCA mutation is annually. However, studies on tumour doubling times indicate that some tumours grow faster. To assess the value of more frequent screening we numerically simulated annual and 6 monthly screening based on reported tumour doubling times in women with the BRCA mutation. For annual screening, the simulation predicted 14% of cancers with poor prognosis (diameter > 2 cm), in line with clinical studies. For 6 monthly screening the simulation predicted 3% with poor prognosis. Therefore, 6 monthly screening should yield a substantial reduction in tumours with a poor prognoses .