We describe the analysis of 1023 unrelated patients with suspicion of hereditary cancer using an in house-designed 135 gene panel. We identified thirteen (1.37%) patients with two pathogenic mutations in dominant cancer-predisposing genes, representing 5.7% (13/226) of patients with pathogenic mutations. This phenomenon is known as Multilocus Inherited Neoplasia Alleles Syndrome (MINAS) and has been potentially linked to more severe clinical manifestations. Most of these cases (10/13) presented clinical manifestations associated with only one of the mutations identified although a more severe phenotype in biallelic CHEK2 and other DNA repair cancer-predisposing genes is observed. Our results highlight the need to collect these cases in a common database with prospective follow-up in order to improve our knowledge of the clinical relevance and consequences of MINAS. (https://jmg.bmj.com/content/early/2018/12/22/jmedgenet-2018-105700 )