Context: Medullary carcinoma (MC) is a special type of breast cancer that has a better prognosis than atypical medullary carcinoma (AMC) and high-grade invasive ductal carcinoma (HGIDC) with prominent lymphocytic infiltrates. What accounts for the different clinical courses of these carcinomas, despite their similar histology, is unknown. To address this issue, we performed a comparative study of amplification and overexpression of HER-2/neu and expression of several other important biochemical markers (p53, MIB1, and estrogen receptor [ER]/progesterone receptor [PR]) in these 3 cancer groups.
Objective: To evaluate HER-2/neu, p53, MIB1, and ER/PR as markers in the differential diagnosis of MC, AMC, and HGIDC.Design.-Nine cases of MC, 13 cases of AMC, and 16 cases of HGIDC with prominent lymphocytic infiltrates were identified according to strict histologic criteria. All tests were performed on formalin-fixed, paraffin-embedded archival tissues. HER-2/neu gene amplification was examined by fluorescence in situ hybridization using PathVysion HER-2 DNA probes. Expression of HER-2/neu, p53, MIB1, and ER/PR was detected by immunohistochemistry. chi2 and Student t tests were applied for statistical analyses.
Results: None of 9 cases of MC examined had either amplification or overexpression of HER-2/neu (0%). In contrast, HER-2/neu amplification was observed in AMC (46%, P <.025) and HGIDC (56%, P <.005). All 3 categories of tumors had similar percentages of expression of p53 (78% of MC, 77% of AMC, and 69% of HGIDC) and MIB1 (89% of MC, 92% of AMC, and 94% of HGIDC). Immunostaining for ER/PR was rarely positive in either MC or AMC, and there were no significant differences of expression of ER/PR between these 2 lesions (P >.05). However, the expression rate of ER/PR (31%/44%) in HGIDC is higher than in both MC (P =.05) and AMC (P =.01).
Conclusions: Medullary carcinoma of breast is distinct from AMC and HGIDC with prominent lymphocytic infiltrates in amplification and overexpression of HER-2/neu. This difference may account for its different clinical and biological behavior, and may potentially aid in diagnosis and management of these groups of patients.