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Background <p>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.</p> Methods <p>Patients with extraperitoneal T3/T4 N0/N + rectal adenocarcinoma (&lt; 10&#xa0;cm) treated with radiotherapy (5 × 5&#xa0;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).</p> Results <p>A total of 40 patients were included (median age, 66&#xa0;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&#xa0;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 (<i>p</i> &lt; 0.05).</p> Conclusions <p>In this study, ypT0-2 cases were characterized by&#xa0;a&#xa0;predominantly&#xa0;solid regression pattern,&#xa0;absence of MIS, and no&#xa0;lymph node involvement. These findings may contribute to defining resection margins and&#xa0;guiding&#xa0;the selection of surgical techniques.</p>

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

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月17日

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  • 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

摘要

Background

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.

Methods

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).

Results

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).

Conclusions

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.