We have collected the largest world series of patients with FAP (Familial Adenomatous Polyposis) associated FNMTC (n = 18, all females) and were the first to show a significant genotype-phenotype correlation, suggesting that most of APC (Adenomatous Polyposis Coli) germline mutations in patients with FAP associated FNMTC are located in a well defined genomic area, that is, 5′ to codon 1200 [3–17]. The gene discussed is APC; the disease is Familial adenomatous polyposis.