Tumor regression pattern and distribution of residual tumor cells in potential candidates for local excision of rectal cancer: a prospective cohort study.

Authors

A Gheller, D B Basílio, J S Córes, C C P Coelho, L de Araújo, A C Melo, G I B de Meloe Patriarca da Silva Neiva, D da Motta Girardi, A R Aiza, J B de Sousa

Published in

Techniques in coloproctology. Jun 17, 2026. Epub Jun 17, 2026.

Abstract

Understanding the patterns of regression and distribution of residual tumor cells (RTCs) is crucial for selecting appropriate candidates for local excision of ypT0-2 rectal cancer.
Patients with extraperitoneal T3/T4 N0/N + rectal adenocarcinoma (< 10 cm) treated with radiotherapy (5 × 5 Gy) followed by six cycles of CAPOX chemotherapy were prospectively analyzed. The tumor regression pattern was classified as solid or fragmented, and microscopic intramural spread (MIS) was measured. A novel RTC distribution model was used: type I (luminal), type II (invasive front), type III (concentric), and type IV (random).
A total of 40 patients were included (median age, 66 years; 57.5% male). Of these, 19 (47.5%) had ypT0-2 tumors: 5 ypT0, 3 ypT1, and 11 ypT2. There was no lymph node involvement, and only two (10.5%) showed a fragmented pattern; both ypT2. MIS was present in four cases (21.0%); all ypT2. The greatest MIS extension was 8 mm. All three ypT1 cases had RTCs in the mucosa (100%). Among 11 ypT2 cases, RTCs were found in the mucosa in 10 (90.9%) and in the submucosa in 9 (81.8%). RTC distribution was type I in 16 cases (84.2%). Magnetic resonance imaging (MRI) tumor regression grades 1-2, RTC type I distribution, absence of MIS, and pathologic complete response were significantly associated with the occurrence of ypT0-2 (p < 0.05).
In this study, ypT0-2 cases were characterized by a predominantly solid regression pattern, absence of MIS, and no lymph node involvement. These findings may contribute to defining resection margins and guiding the selection of surgical techniques.

PMID:
42307785
Bibliographic data and abstract were imported from PubMed on 17 Jun 2026.

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