Women with a strong family history of breast cancer, with multicentric tumor foci in one breast, and with in situ lobular carcinoma have a high incidence of bilateral breast cancer, synchronous or metachronous (Heron

multicentric tumor foci in one breast, and in situ lobular carcinoma increase the risk of bilateral breast cancer (BBC), synchronous or metachronous. Synchronous tumors are designated as simultaneous breast carcinoma if they appear at the same time. The CD44 family and cadherin/catenin immunophenotype of this group of BBCs has not yet been evaluated. The aim of this study was to compare clinicopathological characteristics and immunohistochemical profiles of simultaneous BBC and corresponding lymph node metastases in eight patients. Methods and results: In toto 15 primary and 9 metastatic tumors were evaluated. The expression of CD44 variant isoforms, ß-catenin, E, P and N-cadherin were evaluated by immunohistochemistry. Rare types of breast carcinoma were frequent in this group of patients. There were 6 pleomorphic lobular, 5 invasive ductal of usual type, 3 atypical medullary carcinomas, 2 mucinous and one invasive micropapillary carcinoma. The expression CD44v6 was most frequent, followed by CD44v3-10, CD44v5, and CD44v3. CD44v4 was generally not expressed. E-cadherin was expressed in 80% primary tumors, 40% expressed N-cadherin, and 66% expressed P-cadherin. Conclusions: Generally, simultaneous carcinomas had different morphology and different immunophenotype. Each primary tumor was more similar to its corresponding metastatic tumor than to the contralateral primary tumor.