The analysis of the concordance between the primary site and the synchronous or metachronous tumour incidence rate led the authors to conclude that breast cancer is the most frequent multiple cancer, especially when it coexists with genetic syndromes, such as breast cancer gene 1 and 2 (BRCA1 and BRCA2) gene mutations, Li-Fraumeni syndrome, hereditary diffuse gastric cancer, Peutz–Jeghers syndrome and PTEN hamartoma tumour syndrome [14, 15]. Here, BRCA1 is linked to breast cancer.