[213] Do True Mixed Invasive Ductal and Lobular Carcinomas of the Breast Exist?

A Heimann, C Tornos, Z Schreiber, P Kane, S Liang, B O'Hea, M Singh, J Liu. Stony Brook University Medical Center, Stony Brook, NY

Background: Invasive breast carcinomas can be divided into invasive ductal (IDC) and invasive lobular (ILC) type, based on histologic and cytologic features. There is a small group of invasive breast tumors showing features of both ductal and lobular neoplasia. Pathologists frequently classify these as invasive mammary carcinomas with mixed ductal and lobular features. Are these tumors truly mixed or are they ductal or lobular carcinomas with areas mimicking dual differentiation? A study of this subset of tumors may give us insight as to the frequency of true mixed tumors, and allow one to better predict risk of bilaterality, and route of metastases in these patients.
Design: With a computer search we identified 51 cases of invasive mammary carcinoma with mixed ductal and lobular features based on histomorphology from 2005-2009 (10 needle biopsies and 41 lumpectomies or mastectomies). E-cadherin immunostain was performed in all cases on sections that showed dual histology. Both H&E and immunostains were reviewed together, and presence or absence of E-cadherin was assessed in both components.
Results: The E-cadherin stain was diffusely and strongly positive in 35 cases and these were re-classified as IDC. In 8 cases, all tumor cells were negative for E-cadherin and they were re-classified as ILC. In the remaining 8 cases, the tumors had both positive and negative components. In five of these 8 cases, E-cadherin positive and negative tumor cells were present in the same areas, and these cases were classified as true mixed tumors. In two cases, two separate tumor masses were identified in the same breast; one was positive and the other negative, and two separate diagnoses were rendered; one of these two cases had E-cadherin negative tumor cells metastatic to the lymph node. In one case, all tumor cells in the breast mass were positive for E-cadherin, but the metastases in the axilla showed both E-cadherin positive and negative tumor cells, suggesting a true mixed neoplasm in which the lobular component may not have been sampled.
Conclusions: Most tumors with mixed ductal and lobular features on H&E are pure IDC (68.6%), with few being pure ILC (15.7%). True mixed invasive mammary carcinomas with ductal and lobular immunophenotypes (E-cadherin positive cells and E-cadherin negative cells in the same tumor mass) do exist, but they make up only a small fraction of the cases (9.8%).
Category: Breast

Tuesday, March 23, 2010 9:30 AM

Poster Session III # 40, Tuesday Morning


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