Final answer:
The second hit in sporadic breast cancers with BRCA1 or BRCA2 mutations is often methylation of the BRCA1 or BRCA2 promoter.
Step-by-step explanation:
In addition to loss of heterozygosity, the second hit in sporadic breast cancers with breast cancer gene 1 (BRCA1) or breast cancer gene 2 (BRCA2) mutations is often Methylation of the BRCA1 or BRCA2 promoter.