BACKGROUND: Rectal cancer is the sixth most common neoplasm in Spain. In the early stages (pT1-N0), the treatment of choice is transanal endoscopic microsurgery. Treatment may be expanded to radical surgery if there are poor prognostic factors for the presence of metastatic lymph nodes and a risk of recurrence (up to 29%). The most determining histopathological factor is the degree of submucosal invasion. There are different classical classifications to assess this invasion, which pose difficulties in establishing objective and reproducible measurements. Casalots et al. propose a new classification (Taulí-T1) based on the measurement of residual healthy submucosa (hrSB), hypothesizing that a greater amount of healthy submucosa correlates with a better prognosis. Results show less healthy submucosa in the recurrence group, with a trend towards statistical significance (p=0.09).

OBJECTIVE: To compare the Taulí-T1 classification with conventional quantitative classifications (Kitajima, Ueno) and qualitative classifications (sm1, sm2, and sm3 by Kudo and Kikuchi).

METHODOLOGY: A multicenter observational retrospective cohort study comparing the Taulí-T1 classification with classical classifications in 317 patients with stage pT1 rectal adenocarcinoma, following the STROBE guidelines. The main variable is the measurement of tumor invasion in µm through hrSB, compared to the invasion of quantitative (Kitajima and Ueno) and qualitative (Kudo and Kikuchi) classical classifications. Concordance will be assessed with the intraclass correlation coefficient for quantitative variables and Cohen's weighted kappa for qualitative variables, with a 95% confidence interval and p<0.005.

HYPOTHESIS: Taulí-T1 classification will have greater clinical utility to classify the stage pT1 rectal adenocarcinomas compared with conventional classifications.

OBJECTIVE: The main objective of the study is to compare the Taulí-T1 classification versus the conventional quantitative methods (Kitajima, Ueno) and qualitative ones (sm1, sm2 and sm3 of Kudo and Kikuchi), through a multicenter cohort study of the TAUTEM group.

STUDY DESIGN:

Multicenter observational retrospective cohort study that compares the Taulí-T1 classification with the classic classifications for stage pT1 of rectal adenocarcinoma.

The study participants will be patients diagnosed with rectal cancer who underwent surgery using transanal endoscopic surgery technique (TME, TEO or TAMIS) and histopathologically diagnosed with stage pT1 rectal adenocarcinoma. To calculate the sample size, an alpha error of 0.05 was used with a confidence level of 95%, with a precision of 0.05 and an estimate of the prevalence of pT1 recurrence of 29%. A sample of 317 patients will be required.

The main variable to be studied is the measurement of tumor invasion in µm by measuring the healthy residual submucosa (hrSB) with the Taulí-T1 classification, in comparison with the measurement of invasion of the classic quantitative (Kitajima and Ueno) and qualitative classifications (Kudo and Kikuchi).

The secondary variables to be assessed are: demographic and macroscopic data of the tumor and histopathological variables (tumor morphology, measurement of the submucosa in the area of the lesion and in the healthy area, presence or absence of muscularis mucosa and muscularis propria, assessment of resection margins, histological differentiation degree, presence of adenocarcinoma on adenoma, presence of poor prognostic factors -lymphatic, perineural and vascular invasion, tumor budding-). Surgical data will also be collected (type of surgery, location of the tumor and distance from the anal margin, integrity of the specimen) and clinical data (neoadjuvant treatment, recurrences, appearance of lymphadenopathy, survival).

Inclusion Criteria:

• Rectal adenocarcinoma.
• Histopathologically diagnosed with stage pT1.
• Patients treated with transanal endoscopic surgery technique (TME, TEO or TAMIS).
• Patients who have received prior neoadjuvant treatment (radiotherapy and/or chemotherapy).
• Over 18 years.

Exclusion Criteria:

• Patients treated with other surgical techniques other than transanal endoscopic surgery.
• Tumors other than adenocarcinoma.
• Locations other than rectum.

Cohort of patients diagnosed with rectal cancer who underwent surgery using transanal endoscopic surgery technique (TME, TEO or TAMIS) and histopathologically diagnosed with stage pT1 rectal adenocarcinoma. Patients who have received prior neoadjuvant treatment (radiotherapy and/or chemotherapy) will also be included, but both histological findings and their recurrence and survival data will be analyzed separately.