Subtyping of Non-Small Cell Lung Carcinoma into Adenocarcinoma and Squamous Cell Carcinoma by Cytological Structural Features.

Introduction: This study aimed to clarify the diagnostic structural features in cytology specimens that are useful in subtyping non-small cell lung carcinoma (NSCLC) into adenocarcinoma (ADC) and squamous cell carcinoma (SQCC).

Methods: Cytology specimens (n = 233) of NSCLCs, which included ADCs (n = 149) and SQCCs (n = 84), were analyzed. The following cytological features were evaluated: isolated cell, flat sheet, three-dimensional cluster with irregular arrangement, papillary-like structure, micropapillary-like structure, acinar-like structure, palisading pattern, protrusion of nuclei at the periphery of the cluster, honeycomb pattern, streaming arrangement, three-dimensional sheets with regular arrangement, flattening at the periphery of the cluster, fuzzy pattern at the periphery of the cluster, and mutual inclusion.

Results: ADCs exhibited significantly higher frequencies of flat sheet (p < 0.001), papillary-like structure (p < 0.001), micropapillary-like structure (p = 0.028), acinar-like structure (p < 0.001), and protrusion of nuclei at the periphery of the cluster (p < 0.001) than SQCCs. The latter exhibited significantly higher frequencies of streaming arrangement (p < 0.001), three-dimensional sheets with regular arrangement (p < 0.001), flattening at the periphery of the cluster (p < 0.001), fuzzy pattern at the periphery of the cluster (p < 0.001), and mutual inclusion (p < 0.001) than ADCs.

Discussion: Cytological structural features, such as flat sheet, papillary-like structure, micropapillary-like structure, acinar-like structure, and protrusion of nuclei at the periphery of the cluster, indicated ADC, whereas streaming arrangement, three-dimensional sheets with regular arrangement, flattening at the periphery of the cluster, fuzzy pattern at the periphery of the cluster, and mutual inclusion indicated SQCC. Paying attention to these cytological structural features can enable the accurate subtyping of NSCLC into ADC and SQCC.