Cytological, histological, and immunohistochemical findings of pulmonary carcinomas with basaloid features

Pulmonary basaloid carcinoma (BC), a variant of large cell, nonsmall cell carcinoma (NSCC), and basaloid squamous cell carcinoma (BSQCC) can show features similar to small cell carcinoma (SCC) and large cell neuroendocrine carcinoma (LCNEC). Distinction from SCC, especially on FNA, is therapeutically relevant. We describe cytological, histological, and immunohistochemical features of BC and BSQCC. Numerous cytologic features were documented in cytologic preparations. Similar features and architecture were evaluated in the resections. Immunohistochemical results were recorded. Histologically confirmed BC (n = 3) and BSQCC (n = 3) were included. Five FNAs of SCC, (four with histologic follow-up) were studied for comparison of cytological, histological, and immunohistochemical findings. In cytologic preparations of BC/BSQCC, cells were arranged mostly as tightly cohesive clusters (n = 4) or singly and in clusters (n = 2) with a predominance of clusters. Cytologic features of BC and BSQCC were similar: palisading (n = 6), crush artifact (n = 6), hyperchromasia (n = 5), focal nuclear molding (n = 6; very rare in 2/6), nucleoli, usually pinpoint (n = 3), scant cytoplasm (n = 6), necrosis (n = 5), apoptosis (n = 4), squamous differentiation (n = 1). BSQCC tended to have occasional larger cells, including keratinizing cells in one case. Histologic sections (n = 6) showed neuroendocrine features, including organoid arrangements, nests, and palisading. BC and BSQCC show overlapping features with SCC and LCNEC in cytological and histological specimens. Unlike SCCs, BC/BSQCC lack prominent nuclear molding, show tightly cohesive cell clusters, and demonstrate palisading. However, immunostains were the very helpful and probably necessary to accurately diagnosing BC/BSQCC, which show the immunostaining pattern of p63 (+), HMWCK (+), and TTF-1 (-).