ABSTRACT Lung is a common site of metastasis for squamous cell carcinoma (SqCC), and distinguishing primary lung SqCC from pulmonary metastatic SqCC is critical for clinical decision‐making, including treatment planning. However, no practical histological criteria have been established for routine diagnosis. This study aimed to develop histopathological criteria to differentiate lung SqCC and pulmonary metastatic SqCC. A total of 85 surgical cases (48 primary and 37 metastatic) were collected with clinical background data. Seven histological features were evaluated. Six morphological heterogeneity, dilated airway, interstitial fibrosis (IF), squamous dysplasia (SD), emphysema, RB macrophage were presented as primary‐associated features, while stromal infarction was proposed as metastatic. Seven pathologists scored these features. Primary‐associated findings showed significantly higher score in primary cases. Tumor size (size) was significantly larger in the primary group (median: primary, 30 mm; metastatic, 14 mm; p < 0.001). A multivariate analysis incorporating size produced the “pathological primary formula” based on parameter estimates: 0.70・IF + 0.36・SD + 0.09・size, with an AUC of 0.86, sensitivity of 89.5%, and specificity of 70.2%. These results suggest that the extracted histologic features may provide reproducible criteria for distinguishing primary lung SqCC from pulmonary metastatic SqCC, offering insight into potential diagnostic applications.
Tachibana et al. (Wed,) studied this question.