Gc isoforms alone were not significantly associated with overall or site-specific cancer, with the possible exceptions of increased risk of biliary tract and male breast cancer for individuals with the Gc2-Gc2 isoform and the Gc1f-Gc1s or Gc1f-Gc1f isoforms, respectively, and a reduced risk of melanoma for individuals with the Gc1f-Gc1s or Gc1f-Gc1f isoforms. This evidence concerns the gene GC and male breast carcinoma.