Table 6 Probability of breast cancer cases related to BRCA1 germline mutations for different groups of patients with breast cancer, on the basis of a combination of classical features: age at diagnosis and MAI.

Classification	Decision tree	Number of sporadic cases	Number of cases with BRCA1 mutations	Probability of BRCA1‐related disease (%)	Number of intermediate‐risk cases	Number of high‐risk cases	Number of cases with BRCA2 mutations
Sporadic	Age ⩾54 years and MAI<17	269	0	0	21	4	1
Intermediate	Age ⩾54 years and MAI⩾17	125	2	2	5	1	2
Intermediate	Age <54 years and MAI<17	18	5	22	22	2	2
BRCA1 related	Age <54 years and MAI⩾17	9	15	63	11	12	0

MAI, mitotic activity index.