A 25-year-old female with
familial adenomatous polyposis (FAP) presented with an abdominal
tumor just below the
scar due to a
colectomy performed 15 months previously. This
tumor (
tumor A) measured 7 cm in diameter, was diagnosed as a
desmoid tumor of the abdominal wall, and was excised. Despite the subsequent administration of
sulindac (300 mg daily for 1 year), a
desmoid tumor recurred at the same site. Excision was performed again when the
tumor was 8 cm in diameter, and examination revealed it to consist of a large
tumor (B) and a small
tumor (C) that bulged out from
tumor B. Germ-line APC analysis showed a C deletion at
codon 1460 resulting in a stop
codon. Two somatic mutations were observed in
tumor A: a TCAA deletion at
codon 1068 and a deletion of a
codon at bp 1192-2097. In
tumor B, a somatic mutation was found at
codon 1041 changing CAA to TAA. We could not detect any somatic mutations in
tumor C. We conclude that somatic mutation analysis of the APC gene can be used to identify whether a recurrent
desmoid tumor in a patient with FAP is a new primary
tumor or a recurrence from microscopic remnants of the original
tumor.