The Immunophenotype of Nodular Variant of Medullary Carcinoma of the Breast.

Abstract

The histologic and immunohistochemical profile of typical medullary carcinomas (TMC) of the breast are well established. Among the strict histologic criteria for the diagnosis of TMC is complete circumscription of tumor with pushing borders. Those tumors that do not fulfill all morphologic requirements of TMC are designated as atypical medullary carcinomas (AMC). We herewith describe the histology and immunophenotype of a heretofore undescribed variant of TMC composed of multiple distinctly separate nodules that otherwise meet all other histologic and immunohistochemical phenotypes of TMC. Among 2952 cases of infiltrating mammary carcinomas, 111 (3.8%) met the strict criteria for TMC, including positivity for HLA-DR. Nine of these tumors were composed of multiple separate noncoalescing nodules. Immunohistochemical stains for ER, PR, HER2, and HLA-DR, as well as for p53 and Ki-67 were repeated on these nodular forms. Staining for p63 was used to identify possible intraductal components of these tumors. The age of patients ranged from 34 to 53 years. All 9 patients had negative sentinel lymph nodes. Tumors ranged in the overall size from 2.2 to 3.9 cm and were composed of 3 to 6 distinct nodules ranging in size from 0.2 to 1.1 cm surrounding a larger main tumor nodule. The nodules were composed of syncytial groups of large cells with atypical nuclei and prominent nucleoli. A lymphoplasmacytic infiltrate was present within and around each satellite nodule. Serial sections did not show coalescing of the nodules into a single tumor mass. Similarly, staining for p63 failed to support the possibility of nodules representing intraductal components of main tumor. All tumors were negative for ER, PR, and HER2, but positive for HLA-DR. Eight of 9 tumors were diffusely positive for p53 and all 9 showed a high proliferation index in >70% of tumor cells with Ki-67. We conclude that the nodular variants of medullary carcinomas (nTMC) of the breast are uncommon forms of TMC. They occur in relatively younger women and share the same immunophenotype with TMCs; they are triple negative, express HLA-DR and p53, and show a high proliferative index. As the diagnosis of TMC carries major clinical and prognostic implications, the recognition of its nodular variant becomes equally important.