MIXED SMALL-CELL LARGE-CELL CARCINOMA OF THE LUNG - REPORT OF A CASE WITH CYTOLOGIC FEATURES AND ULTRASTRUCTURAL CORRELATION

BACKGROUND: Mixed small cell/large cell carcinoma of the lung, a chemetherapy- and radiation-resistant subtype of small cell lung cancer, constitutes 4-6% of small cell lung cancer but has been described rarely in the cytopathology literature. CASE: A 64-year-old man presented with a left hilar mass. A concurrent transbronchial biopsy and postbiopsy bronchial washing were performed. The latter presented as loosely cohesive cells, scattered singly, in small clusters, in monolayer sheets and in a perivascular arrangement. The tumor exhibited a wide spectrum of cytomorphology: small cells with pyknotic nuclei and scanty cytoplasm were admixed with larger cells with vesicular nuclei, prominent nucleoli and abundant cytoplasm. Nuclear shape included oval, spindle and peg. Nuclear size was also highly variable. The tumor was retrieved from the transbronchial biopsy and processed for ultrastructural study. CONCLUSION: Based on cytologic-ultrastructural correlations, the seemingly ''mixed'' morphology may have resulted from the rapid degeneration of a single clone of tumor cells: the viable tumor cells were the ''large'' cells, and the dying cells were the ''small'' cells. A novel ultrastructural observation is that the perivascular tumor cells developed peculiar, fingerlike cytoplasmic processes abutting an undulating basement membrane along the thin-walled blood vessel.