Cakir E, Demirag F, Aydin M. Cytopathologic differential diagnosis of small cell carcinoma and poorly differentiated non-small cell carcinoma in bronchial lavage specimens using a regression analysis. APMIS 2010; 118: 150–55. The aim of this study was to determine the most significant cytologic features to differentiate small cell carcinoma (SCC) from poorly differentiated non-small cell carcinoma (NSCC) in bronchial lavage specimens. Bronchial lavage specimens from 35 SCC cases and 63 poorly differentiated NSCC cases were examined and the cytologic parameters reviewed retrospectively. Thirty-five cytologic features considered useful in differential diagnosis were assessed. Statistical analysis indicated that salt and pepper chromatin, small cell size and nuclear molding have more than 90% sensitivity and 70% specificity for SCC cases. Logistic regression analysis demonstrated that the most effective criteria to differentiate SCC from poorly differentiated NSCC are small cell size, salt and pepper chromatin, prominent nucleolus and papilla formation. When these selected variables were used, sensitivity for predicting SCC was 94.3% and specificity 96.8%, and sensitivity for predicting NSCC was 96.8% and specificity 94.3%. There are several cytologic features, which are highly sensitive and specific for distinguishing SCC from NSCC. Nuclear features such as chromatin pattern, and size of the nucleoli and nuclei are more valuable than cytoplasmic features to distinguish between the two.