Here, we present a female with bilateral breast cancer and endometrial adenocarcinoma, where multiplex genetic testing revealed pathogenic mutations in two high-penetrance genes, i.e. TP53 and CDH1. We describe why traditional serial genetic testing would most likely not have elucidated both mutations, which had a tremendous impact on the index patient and her family. Here, TP53 is linked to endometrium adenocarcinoma.