Distinctive histopathological features of lepidic growth predominant node-negative adenocarcinomas 3-5cm in size

Introduction: Adenocarcinoma of the lung is a morphologically heterogeneous group of tumors which includes a variable portion of different histologic subtype components: lepidic growth (LG), and acinar, papillary and solid subtypes. Among these, LG is a non-invasive component which is one of the major histological subtypes in small-sized adenocarcinoma (2. cm or less). However, in large adenocarcinomas (3-5. cm in size), the clinicopathological significance of LG components remains unclear. Methods: A series of 135 lung adenocarcinomas 3-5. cm in size, without lymph node involvement, were reviewed and classified according to their percentage of LG components. We examined the correlation between the percentage of LG components and clinicopathological factors of these tumors. Results: There were 41 (30.4%) tumors with 50% or more LG (LG-predominant group). Female gender (p= 0.039), smoking history of <20 pack-years (p= 0.039), absence of pleural invasion (p= 0.003), and absence of vascular invasion (p< 0.001) were significantly more frequently observed in the LG-predominant group. LG-predominant tumors showed a significantly higher percentage of non-cancerous cell collapse area to tumor area compared with non-LG predominant tumors (p< 0.001). The outcome of the LG-predominant type patients was significantly better than that of the non-LG predominant type patients in both recurrence-free survival (p< 0.001) and overall survival (p< 0.001). Multivariate analysis showed that LG-predominant tumor to be an independent favorable prognostic factor (HR = 0.285, 95% confidence interval: 0.148-0.547, p= 0.014). Conclusion: Node-negative LG-predominant adenocarcinomas of 3-5. cm in size showed less invasiveness compared to non-LG predominant tumors. And LG-predominant type patients had excellent surgical outcome.