This is probably due to the known biological differences between BRCA1 -related cancers, which often have a basal cell phenotype, and sporadic cancers, which usually have a luminal cell phenotype. BRCA1 cancers tend to have little or no associated DCIS so those tell-tale calcifications are absent on mammography. Also, BRCA1 cancers tend to be fleshy with round, pushing borders that give a more benign mammographic appearance than the typical spiculated borders of sporadic cancers.