Tumors of the breast showing dual differentiation: a review

Working formulation of neuroendocrine tumors of the skin and breast

In the skin and breast, endocrine tumors are composed of a heterogeneous mixture of endocrine and exocrine cells. The definition of "pure" endocrine carcinomas is a matter for debate, and as a consequence, there is lack of uniform diagnostic criteria. There are no significant clinical differences in either overall or disease-free survival between matched neoplasms with endocrine and without endocrine differentiation nor between the degree of endocrine differentiation and tumor size, stage, or prevalence of vascular invasion for both sites (skin and breast). Here, endocrine tumors of the skin and breast are grouped respectively into three categories that include most of the neuroendocrine tumors of the skin and breast as seen in routine practice. It was felt that the number of different types of neuroendocrine tumors is so conspicuous that it is impossible to organize them in an orderly classification. It has been proposed therefore, for practical diagnostic routine purposes, to arrange these neoplasms into a working formulation. The latter includes heterogeneous lesions respectively of the skin and breast within the same group that have clinical features in common.

Lobular carcinoma of the breast with hybrid myoepithelial and secretory ("myosecretory") cell differentiation

Three cases of lobular carcinoma of the breast showing a complex morphology that included myoepithelial cell differentiation are reported. One case was a pure in situ acinar lesion, while the other 2 cases were in situ and invasive carcinomas. Three different cell types were seen in these tumors: one was the phenotype commonly seen in the garden variety of in situ lobular carcinoma (LCIS) constituted by noncohesive round to ovoid cells with round nuclei and positivity for epithelial membrane antigen (EMA), estrogen receptor (ER), and progesteron receptor (PR). E-cadherin was negative in these cells. The second type was represented by cohesive elements with irregular nuclei. These cells were immunoreactive for smooth muscle actin, calponin, keratin 14, p63, and e-cadherin. EMA, ER, and PR were consistently negative. The third type, seen in a minority of cell population of case nos. 2 and 3, consisted of cells showing at the same time EMA and smooth muscle actin in their cytoplasm. This type was defined as "hybrid myosecretory cell" to highlight contractile and secretory properties present at the same time. Cells with hybrid features probably indicate that myoepithelial and secretory cells are strictly related and the existence of a stem cell, at least for these cases, is not necessary.