Fig. 1

Display of how to analyze familial risk of BC using a pedigree as an example. Parents and siblings were used to define family history. Familial risk was estimated among the offspring generation. In Fig. 1a (family history of BCa-2), the mother was first diagnosed with cancer A (first primary cancer) at age1 and then BCa-2 at age2. In Fig. 1b (family history of BCa-1), the mother was diagnosed with BCa-1. In Fig. 1c (no family history of cancer), no first-degree relatives were diagnosed with any cancer. BC, breast cancer, cancer A, any cancer other than breast cancer, BCa-1, breast cancer as a first primary malignancy, BCa-2, breast cancer as a second primary malignancy