Prevalence of Skin Lesions in Familial Adenomatous Polyposis: A Marker for Presymptomatic Diagnosis?

Background and Aims. Benign skin tumors such as lipomas, fibromas, and epidermal cysts are among the extracolonic manifestations of familial adenomatous polyposis (FAP). Readily detectable by inspection, they could serve as presymptomatic diagnostic markers to identify FAP patients. We therefore prospectively determined the prevalence of cutaneous lesions in genetically confirmed adenomatous polyposis coli ( APC ) mutation carriers and assessed their potential usefulness in the identification of FAP patients. Methods. Whole‐skin examination was performed in 56 adult APC mutation carriers, compared with a control group ( n = 116). In addition, FAP patients were investigated for the presence of congenital hypertrophy of the retinal pigment epithelium (CHRPE), an established clinical marker for FAP, and a detailed review of medical records was performed. Results. Nearly half of all FAP patients (48.2%) had at least one FAP‐associated skin lesion, compared with one third (34.5%) of controls. Only multiple lipomas and combined skin lesions were significantly more prevalent in APC mutation carriers. CHRPE was observed in 22 (43.1%) of 51 FAP patients, including 14 (37.8%) of 37 individuals with APC mutations outside the CHRPE‐associated region between codons 311 and 1465. Conclusions. Despite a significantly higher prevalence of multiple lipomas, occurring at younger age, and combined skin lesions in APC mutation carriers, the low diagnostic sensitivity of FAP‐associated skin lesions precludes their use as markers for FAP in clinical practice. Based on our findings, the common CHRPE‐associated region should be extended to APC codons 148‐2043.