Polyps and inherited gastrointestinal cancer syndromes: SAQ

This boy cannot be dismissed as having benign isolated juvenile polyps. Four juvenile polyps combined with a strong family history of polyposis and early pancreatic cancer redefine the picture as a juvenile polyposis syndrome until proven otherwise, and his mother's colectomy for hundreds of polyps raises familial adenomatous polyposis as a parallel concern. The questions turn on the diagnostic criteria, the genes and cancer risks, and the surveillance and genetic plan for the child and the family. [1]

Question 1 (10 marks)

Explain how you would classify this child's polyps, the criteria that separate an isolated juvenile polyp from a syndrome, and which inherited syndromes you would consider in this family. [1]

The decisive first step is histology and polyp count. An isolated juvenile polyp is a benign hamartomatous overgrowth removed once at colonoscopy, but juvenile polyposis syndrome is defined by more than five juvenile polyps in the colorectum, any juvenile polyp elsewhere in the gastrointestinal tract, or any number of juvenile polyps with a family history. This boy has four colonic juvenile polyps and a clear family history, so he meets the syndromic definition, and the history should prompt germline testing rather than reassurance. The juvenile polyp histology with this family pattern points toward juvenile polyposis syndrome caused by SMAD4 or BMPR1A. The mother's colectomy for hundreds of polyps, however, raises familial adenomatous polyposis from an APC mutation, and the aunt's early pancreatic cancer is a recognised extraintestinal malignancy of Peutz-Jeghers and several familial cancer syndromes, so the full differential includes juvenile polyposis, familial adenomatous polyposis, Peutz-Jeghers syndrome, and MUTYH-associated polyposis, distinguished by polyp histology and germline testing rather than by the bleeding alone. [1]