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 |
|---|---|---|---|---|---|---|---|
| MAI, mitotic activity index. | |||||||
| 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 |