Comparison of Peripheral Small-sized Lung Adenocarcinoma and Squamous Cell Carcinoma

<h3>Background/Aim:</h3> The number of lung squamous cell carcinoma (SCC) surgeries in Japan is gradually increasing, and half or more of new lung SCC are peripheral-type. The malignant behavior of peripheral-type lung SCC has not been extensively investigated. This study compared the clinical course of peripheral lung SCC with that of adenocarcinoma. <h3>Patients and Methods:</h3> A total of 565 patients underwent definitive pulmonary resection for primary non-small cell lung cancer from 2021 to 2024. A total of 173 patients had tumors measuring 2 cm or less in diameter and a &gt;0.5 consolidation tumor ratio. Among these, 126 patients with peripheral lesions, cN0, and histological types of adenocarcinoma or SCC were included in this study. <h3>Results:</h3> This study included 100 patients with adenocarcinoma and 26 patients with SCC. Compared to patients with adenocarcinoma, those with SCC were significantly older (<i>p</i>=0.038), and had a higher proportion of males (<i>p</i>=0.060), blood cytokeratin 19 fragment levels (<i>p</i>=0.002), consolidation tumor ratio (<i>p</i>=0.005), incidence of background pulmonary interstitial shadow (<i>p</i>=0.015), standardized uptake values in fluorodeoxyglucose positron emission tomography/computed tomography (<i>p</i>=0.004), and rate of comorbidities. SCC patients tended to undergo wedge resection rather than anatomic resection. Overall (<i>p</i>=0.052) and recurrent-free (<i>p</i>=0.036) survival rates were low in patients with SCC compared to those with adenocarcinoma. Patients with SCC had a high proportion of deaths from other causes. <h3>Conclusion:</h3> The prognosis of patients with peripheral SCC was poorer than that of patients with adenocarcinoma. Possible contributing factors included the tendency to avoid anatomical resection, a high rate of death from other causes, and the high malignancy of the tumors.