Synchronous small cell carcinoma and adenocarcinoma of the lung representing different retinoblastoma tumor suppressor protein status

We report a case of synchronous primary lung cancers —small cell carcinoma and adenocarcinoma. We analyzed the expression of neuropeptides and tumor suppressor gene products in the two carcinomas, using immunohistochemistry. The small cell carcinoma showed absence of retinoblastoma (RB) tumor suppressor protein and the presence of neural differentiation-related protein, while the adenocarcinoma showed expression of RB protein with nuclear localization and the absence of neural protein. These results indicate that different carcinogenic steps may have been involved in the development of small cell carcinoma and adenocarcinoma in this patient.