Co‐occurrence of breast cancer and neuroendocrine tumours: New genetic insights beyond Multiple Endocrine Neoplasia syndromes

Objective Age‐standardized incidence of female breast cancer is 145.1 per 100000/year and 5.86 per 100000/year for neuroendocrine tumours (NET) in Canada. Evidence is scarce about gene variants that may predispose patients to develop both neoplasms. The objective of this study was to identify germline gene variants associated with this combination of tumours. Design and patients A retrospective chart review (2007‐2018) in a tertiary NET referral centre was completed. A series of 9 female patients with concurrent breast cancer and NET is presented. All patients underwent a 37 gene hereditary cancer next‐generation sequencing panel. Results Mean age was 61.4 years (35‐85) at breast cancer diagnosis and 63.4 years (51‐89) at NET diagnosis. Four patients had a pancreatic, three had a small bowel and two had a lung NET. Two patients were known cases of MEN1, and one patient was found to harbour a pathogenic variant in MEN1 and a variant of unknown significance (VUS) in ATM. A second patient was found to harbour a pathogenic variant in APC. A third patient was found to carry a pathogenic variant in PALB2 as well as a VUS in FANCM, MLH1 and STK11. Another patient was found to harbour a VUS in MSH2. One patient was found to carry a pathogenic variant in NTHL1. Conclusion The first cases of a PALB2, an APC and a NTHL1 pathogenic variants in patients with both breast cancer and NET were presented. NGS testing should be considered in specific patients with this combination of neoplasms, as certain germline variants beyond MEN1, have important implications for cancer surveillance. This study is a retrospective chart review carried out in a tertiary neuroendocrine tumour referral centre. We present a series of 9 cases of co‐occurrence of female breast cancer and neuroendocrine tumours in which we identified the first cases of a PALB2, an APC and a NTHL1 pathogenic variant. Our novel findings have important implications for clinicians, and they illustrate that germline cancer gene panel testing should be considered in specific patients with a co‐occurrence of breast cancer and NET, as certain germline variants beyond MEN syndromes have important implications for cancer surveillance.