The clinical features of polymerase proof-reading associated polyposis (PPAP) and recommendations for patient management

Abstract

Pathogenic germline exonuclease domain (ED) variants of POLE and POLD1 cause the Mendelian dominant condition polymerase proof-reading associated polyposis (PPAP). We aimed to describe the clinical features of all PPAP patients with probably pathogenic variants. We identified patients with a variants mapping to the EDs of POLE or POLD1 from cancer genetics clinics, a colorectal cancer (CRC) clinical trial, and systematic review of the literature. We used multiple evidence sources to separate ED variants into those with strong evidence of pathogenicity and those of uncertain importance. We performed quantitative analysis of the risk of CRC, colorectal adenomas, endometrial cancer or any cancer in the former group. 132 individuals carried a probably pathogenic ED variant (105 POLE, 27 POLD1). The earliest malignancy was colorectal cancer at 14. The most common tumour types were colorectal, followed by endometrial in POLD1 heterozygotes and duodenal in POLE heterozygotes. POLD1-mutant cases were at a significantly higher risk of endometrial cancer than POLE heterozygotes. Five individuals with a POLE pathogenic variant, but none with a POLD1 pathogenic variant, developed ovarian cancer. Nine patients with POLE pathogenic variants and one with a POLD1 pathogenic variant developed brain tumours. Our data provide important evidence for PPAP management. Colonoscopic surveillance is recommended from age 14 and upper-gastrointestinal surveillance from age 25. The management of other tumour risks remains uncertain, but surveillance should be considered. In the absence of strong genotype-phenotype associations, these recommendations should apply to all PPAP patients.

Keywords: Exonuclease domain mutation; POLD1; POLE; PPAP.

Fig. 1

Pedigrees of the families in which new carriers of POLE and POLD1 ED probably pathogenic variants were found

Fig. 2

Graphs showing the cumulative risk of developing CRC, colorectal adenomas, endometrial cancer and any cancer in carriers of probably pathogenic variants in POLE and POLD1

Fig. 3

Graphs showing the cumulative risk of developing CRC, colorectal adenomas and any cancer in male and female carriers of probably pathogenic variants in POLE and POLD1. POLD1 and POLE ED variant heterozygotes have been grouped together. Shaded areas represent 95% confidence intervals