The role of cytokeratins 20 and 7 and estrogen receptor analysis in separation of metastatic lobular carcinoma of the breast and metastatic signet ring cell carcinoma of the gastrointestinal tract

Metastatic signet ring cell carcinomas of unknown primary site can represen t a clinical problem. Gastrointestinal signet ring cell carcinomas and inva sive lobular carcinomas of the breast are the most common sources of these metastases. Immunohistochemical algorithms have been successfully used in t he search for the unknown primary adenocarcinomas. In the present study a s eries of primary invasive lobular breast carcinomas (79 cases) and their me tastases and a series of gastrointestinal signet ring cell carcinomas (22 p rimary and 13 metastases) were stained with monoclonal antibodies for cytok eratin (CK) 20 and CR7 and for estrogen receptors (ER). The staining was ev aluated as negative (no staining), focally (less than 10% of the tumor cell s stained) or diffusely positive. All the primary and metastatic gastrointe stinal signet ring cell carcinomas proved to be CK20 positive, while only 2 /79 (3%) of the primary and 1/21 metastatic lobular carcinomas (5%) stained positively for this CK. None of the gastrointestinal carcinomas and the ma jority of the lobular carcinomas expressed ER. The majority of the tumors w ere CK7+. Using CK20 alone, 33 of 34 metastases could be properly classifie d as gastrointestinal (CK20+) or mammary (CK20-). ER identified 31/34 of br east cancer metastases. By combining the results of CK20 and ER staining al l the metastases could be properly classified as the CK20+/ER- pattern iden tified all the gastrointestinal tumors.