Surgical Pathology Criteria–

Familial Adenomatous Polyposis

Differential Diagnosis

HNPCC / Lynch Syndrome Familial Adenomatous Polyposis
May have family history of characteristic associated neoplasms Family history of early onset of colorectal polyps
Duodenal adenoma and carcinoma rare Personal or family history of duodenal adenoma common, carcinoma may occur
Adenomas if present are only moderately increased ≥100 adenomas in classic cases
Genetic and immunohistologic evidence of mismatch repair deficiency No evidence of mismatch repair deficiency
APC mutation not present APC mutation detectable in 80%
Attenuated FAP may be very difficult to distinguish from HNPCC as it has fewer adenomas and later presentation and frequent right sided carcinoma

 

MUTYH Associated Polyposis Attenuated Familial Adenomatous Polyposis
Germline mutation detected in MUTYH gene No MUTYH mutation
No germline APC mutation May have detectable APC mutation (10% of cases)
Autosomal recessive Autosomal dominant
18-30% of APC mutation negative attenuated FAP may instead be due to MUTYH mutation

 

Juvenile Polyposis Familial Adenomatous Polyposis
Dysplasia, if present is focal Multiple adenomatous polyps, all with cytologic dysplasia
Mucous retention cysts prominent Lacks mucous retention cysts

 

Hereditary Mixed Polyposis Familial Adenomatous Polyposis
Mixtures of adenomatous and juvenile type polyps Colorectal polyps are all adenomatous
Polyps may have mixed adenomatous and juvenile features Colorectal polyps lack juvenile features
No extra-colorectal associated lesions May be associated with duodenal adenomas, gastric fundic gland polyps, desmoid tumors and other extra-gi disorders
No APC mutation Mutation in APC gene

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