Dual differentiation in small cell carcinoma (oat cell carcinoma) of the lung

Two cases of small cell "undifferentiated" carcinoma (oat cell carcinoma) of the lung with dual neurosecretory and squamous differentiation are reported. One was treated with various regimens of chemotherapy and radiotherapy; the other was untreated at the time of biopsy. By electron microscopy, the same tumor cells showed membrane-bound, dense-core, neurosecretory-type granules and bundles of tonofibrils denoting squamous differentiation. This dual differentiation underlies the difficulty of ascribing an exclusively neural histogenesis to small cell carcinomas with neurosecretory-type granules. It is possible that entoderm-associated neuroectodermal tumors develop features of autochthonous entodermal tumors as a result of microenvironmental influences. An alternative hypothesis would be that small cell tumors are derived from basal reserve bronchoepithelial cells with pluripotentialities.