The Clinical Significance of Elastic Lamina Invasion in Patients with pStage II Colorectal Cancer: A Notable Prognostic Indicator

Background Some colorectal cancers (CRCs) are clinically diagnosed as cT4a with serosal invasion (SI). However, the cT4a is most often underdiagnosed pathologically as pT3 without SI by hematoxylin-eosin (H&E) staining alone. Using Elastica-Van Gieson (EVG) staining, some pT3 tumors invade the elastic lamina (EL), which extends just below the serosal layer. Recently, EL invasion (ELI) has been described as a poor prognostic factor for disease-free (DFS) and overall survival (OS) in patients with pStage II CRC. However, its clinicopathological significance remains unclear due to the limited number of studies and poor understanding of ELI. Objective This study investigated the association between ELI and prognosis. Methods After 1982, pathological diagnosis was routinely performed using H&E and EVG staining methods and long-term follow up was performed until 2016. All clinicopathological features including ELI were prospectively registered into our computer and 605 patients with pStage II CRC were collected from the database. Based on ELI status, pT3 was divided into pathological three categories; pT3ELI − was defined as pT3a, pT3ELI + as pT3b and unidentified EL (pT3EL−) as pT3u. Results Using H&E staining alone, gross cT4a was most often pathologically underdiagnosed as pT3 (93.4%) and very rarely as pT4a, resulting in a large diagnostic discrepancy. Using EVG staining, 59.2% of cT4a cases were diagnosed as pT3b. The 10-year DFS and OS rates were similar for pT3a and pT3u. However, the 10-year DFS and OS rates of pT3b were significantly lower than that of pT3a (76.8% vs. 95.8%, p  < 0.001 and 58.7% vs. 69.3%, p  = 0.003, respectively) but did not differ from that of pT4a (74.3%, p  = 0.771 and 51.5%, p  = 0.157, respectively). Multivariate analysis identified ELI as the strongest independent risk factor for recurrence and CRC-specific death ( p  < 0.0001). Conclusions A better understanding of ELI allows us to reconsider the diagnostic discrepancy of serosal invasion, i.e., pT3b should be considered pT4a. The ELI-based subclassification of pT3 is expected to be incorporated into the TNM staging system in the future. ELI is a notable prognostic indicator in patients with pStage II CRC.