T1 Rectal Adenocarcinoma: a Different Way to Measure Tumoral Invasion Based on the Healthy Residual Submucosa with Its Prognosis and Therapeutic Implications

Background: Surgical treatment of early rectal cancer T1 is either local excision or total mesorectal excision. The choice of surgery is based on the risk of metastatic lymph node involvement. The most important factor to consider is the degree of submucosal invasion. We present a different way to measure tumoral invasion derived from the measurement of the healthy residual submucosa with its prognosis and therapeutic implications Methods: Observational study of tumor submucosal invasion in patients undergoing transanal endoscopic microsurgery was conducted. Parameters evaluated are submucosal invasion, measuring the healthy residual submucosa at the point of maximum invasion; macroscopic morphology of the tumor; presence of muscularis mucosa, muscularis propria, and measurement of submucosa in the tumor area and the healthy area. The classification proposed is compared with the ones previously published. Results: Eighty consecutive patients diagnosed with T1 rectal cancer underwent transanal endoscopic microsurgery. Seventeen tumors (21.3%) were polypoid. En bloc resection was achieved in 77 (96.3%). The muscularis mucosa was present in 28 (35%), and the muscularis propria in 77 (96.3%) (p < 0.001). The healthy residual submucosa in the tumor area measured 2,343 ± 1,869 μm. Agreement was moderate with the Kikuchi classification (kappa 0.58) and very good with the Kudo classification (kappa 0.87). Conclusions: We describe a method for measuring submucosal invasion in T1 rectal cancer which does not depend on the morphology of the lesion or on the presence of the muscularis mucosa. It can be applied to all T1 classifications of the digestive tract in which the muscularis propria is present.