3′ Mutation of the APC Gene and Family History of FAP in a Patient With Apparently Sporadic Desmoid Tumors

Desmoid tumors may occur sporadically or as part of the extraintestinal manifestations of familial adenomatous polyposis. Different phenotypes have been described and some genotype-phenotype correlations have been raised, associated with different sites of germline mutations in the adenomatous polyposis coli (APC) gene. We report on a 42-year-old woman ascertained for a large desmoid tumor of the anterior chest wall with pleural involvement, which persistently recurred despite a decade of treatment including hormone therapy, chemotherapy, and surgery. Spontaneous disappearance of the tumor was later noted after 1 year without any treatment and confirmed after 4 years of regular follow-up. Repeated colonoscopies were normal in the proband and DNA sequencing showed a frameshift mutation due to a single adenosine deletion at position 5772 (codon 1924). This mutation, located in the exon 15 at the 3' end of the APC gene, leads to an unusual and late onset phenotype. The pedigree revealed other isolated or familial adenomatous polyposis-associated cases of desmoid tumors. This family report shows that a molecular analysis of the APC gene should be performed in familial desmoid tumors for accurate genetic counseling and follow-up.