We retrospectively analyzed the data of 328 patients with HER2-positive pure ductal or lobular breast carcinoma, comparing clinical and biological data at diagnosis as well as outcome between the 2 histologies.
Other characteristics, less strongly associated with HER2-positive status, showed either no annual variation (nodal and metastatic status, tumour size) or an annual positive trend (mean age, lobular carcinomas) or an annual negative trend (ductal carcinomas).
Immunohistochemical analysis detected robust and frequent expression of C35 protein, including 32% of grade 1 and 66% of grades 2 and 3 infiltrating ductal carcinomas of the breast (in contrast to 20% overexpressing HER-2/neu), 38% of infiltrating lobular carcinoma (typically HER-2/neu negative), as well as tumors arising in other tissues.
HER-2/neu positivity was observed in 34% of grade 3 ductal carcinomas, 11.4% of grade 2 ductal carcinomas, 3.2% of grade 1 ductal carcinomas, and 3.2% of lobular carcinomas.
Immunostaining consistent with c-erbB-2 overexpression was found in 10 out of 50 cases of infiltrating ductal carcinoma (NOS), one of 24 infiltrating lobular carcinomas and one of seven medullary carcinomas only.