Background:
Lobular breast carcinoma (LBC) is considered an exceptionally rare disease in men, including only 1% of all male breast malignancies. The majority of LBCs have negative immunohistochemical staining for E-cadherin (CDH1) expression, and the loss of CDH1 function was traditionally implicated in the tumorigenesis of diffuse gastric cancer as well as LBC. It is well recognized that LBC in women could be involved in both hereditary breast and ovarian cancer (HBOC) and hereditary diffuse gastric cancer (HDGC) syndromes; however, there are no data present in literature about the involvement of male LBC in these inherited conditions.
Methods:

BRCA1, BRCA2, and CDH1 genes were performed on DNA from peripheral blood using next-generation sequencing (NGS), Sanger sequencing, and multiplex ligation-dependent probe amplification analyses. BRCA2 and CDH1 somatic gene analyses were performed on breast tumoral DNA using the NGS sequencing approach.
Results and conclusions:
Here, we describe two men affected by LBC, the carriers of a pathogenic variant of BRCA2 and CDH1 genes, respectively. Our data, including somatic and germline results, demonstrate a strong relationship between male LBC and HBOC/HDGC syndromes, excluding a sporadic origin of LBC in these two patients. Male LBC could represent a sentinel cancer for inherited syndrome identification, and early identification of cancer susceptibility could improve cancer prevention both for men and women in these families. The history of the LBC patient carrier of the CDH1 variant suggests to include male LBC genetic testing criteria and male breast surveillance in HDGC guidelines.