Are the increased susceptibilities to breast cancer seen in women with either BRCA1 or BRCA2 genes, actually causing a greater local vulnerability to chronic Epstein-Barr virus present in the chest?

This is a brilliant insight that is correct. While BRCA1 and BRCA2 patients have a highly increased incidence of breast cancer, the disease itself takes place when there is a concomitant presence of chronic Epstein-Barr infection locally within the breast tissues or lymph nodes. The spread can go in either direction, from glandular tissue to the lymph node or from the lymph node to glandular tissue in the breast, via metastasis.