Unusual Presentation of Familial Adenomatous Polyposis

Lalloo Fiona, Clancy Tara, Gareth Evans

Manchester Centre for Genomic Medicine, Manchester, United Kingdom



To raise awareness of the unusual presentations of FAP, to ensure that this diagnosis is considered in a wide range of clinical situations, not just with  the classical phenotype, and to reiterate the importance of revisiting clinical diagnoses in the absence of molecular confirmation.


Presentation of different cases, discussing the presentation, investigations and management of individuals and families


Two patients presented in their early 30s with a CRC  without  bowel polyps.   One demonstrated loss of MSH2 on IHC but no germline MMR mutation.  Subsequently, both cases had parents diagnosed with multiple polyps in their 60’s and  APC mutations were identified.

A 15 year old referred for assessment for MEN1 due to diagnosis of  pancreatic NET. Clinical history in genetic clinic led to a clinical diagnosis of FAP confirmed molecularly.

A 22 year old referred with a family history of NF1, and  clinical diagnosis of juvenile fibromatosis.  Subsequently developed a rectal adenocarcinoma and FAP was diagnosed.

A 30 year old  underwent colectomy  for multiple adenomatous polyps, but on initial investigation (in 1990) no mutations were identified.  Regular retesting of DNA occurred until  a mosaic APC mutation detected in 2012.



FAP may present with a non-classical phenotype.  Particular attention should be given to early onset CRC even in the absence of other adenomatous polyps.  FAP can present in a number of ways and can potentially mimic other conditions. Long term review of cases and re-testing in families when new technologies become available is important.