In sporadic (osteo)sarcomas, lung cancers, breast cancers, ovarian cancers, colon cancers and haematopoietic neoplasms, CHEK2 was found to be rarely mutated (Bell et al, 1999; Haruki et al, 2000; Hofmann et al, 2001; Tavor et al, 2001; Aktas et al, 2002; Hangaishi et al, 2002; Ingvarsson et al, 2002; Miller et al, 2002). Here, CHEK2 is linked to breast carcinoma.