Women with a mutant BRCA1 or BRCA2 gene have a high risk of breast cancer (50–85%) because BRCA deficient cells have a decreased ability to repair damaged DNA. The histopathological changes in these cancers are often characteristic of the mutant gene but the reasons for these differences are unknown.

In a paper published in the 22 February New England Journal of Medicine, Hedenfalk et al found that genes expressed by breast cancers with BRCA1 mutations are distinctive from those expressed by cancers with BRCA2 mutations.

Ingrid Hedenfalk and colleagues studied primary tumour RNA samples from carriers of the BRCA1 or BRCA2 mutations, and from patients with sporadic cases of breast cancer. Using a microarray of 6,512 complementary DNA clones of 5,361 genes they identified 176 genes expressed different in the two types of tumour (N Engl J Med 2001, 344:539-548).

These findings suggest that a heritable mutation influences...