The proportion of patients heterozygous for PV in established PDAC-susceptibility genes in subgroup #1 (15/56; 26.8%) was similar in Belgian (26.5%) and Czech (27.3%) patients (Table 3) and concerned 5 × BRCA2, 3 × ATM, 3 × Lynch syndrome genes, 2 × BRCA1, 1 × TP53 and 1 × CDKN2A. Additionally, three patients harbored the c.1100delC variant in CHEK2 and another one had a PV in FANCM. Here, ATM is linked to acquired polycythemia vera.