# Do not expect an endoluminal complete response to identify a pathologic complete response in rectal cancer!

## TL;DR

This study shows that endoluminal complete response does not always mean a pathologic complete response in rectal cancer patients after treatment.

## Contribution

The study reveals that half of pathologic complete responses are not reflected in endoluminal findings, challenging assumptions about treatment response assessment.

## Key findings

- Only 45% of pathologic complete responses achieved an endoluminal complete response.
- Endoluminal complete response had 55% sensitivity and 96% specificity for identifying pathologic complete response.
- Mid-rectal tumors with residual size ≤ 4 cm² were significantly associated with pathologic complete response.

## Abstract

•Correlation between pathologic complete response and endoluminal complete response.•Half of pathologic complete responses do not achieve an endoluminal complete response.•Gross findings do not perfectly reflect microscopic findings.

Correlation between pathologic complete response and endoluminal complete response.

Half of pathologic complete responses do not achieve an endoluminal complete response.

Gross findings do not perfectly reflect microscopic findings.

To examine the relationship between endoluminal and pathologic complete response after chemoradiotherapy for rectal cancer and identify predictors of a pathologic complete response.

The anatomic pathology reports of 102 consecutive patients with rectal cancer who underwent neoadjuvant chemoradiotherapy followed by proctectomy between 2013 and 2017 were reviewed for the presence or absence of endoluminal complete response. The presence of endoluminal complete response was compared with the anatomopathological stage. The residual lesion area was compared with the final pathologic stage to identify predictors of complete response.

Of 102 patients, 20 (19.6 %) achieved a pathologic complete response (ypT0N0). Of these, 9 (45 %) did not achieve an endoluminal complete response. The presence of endoluminal complete response had a sensitivity of 55.00 %, specificity of 96.34 %, and accuracy of 88.24 % to identify ypT0N0. The presence of endoluminal complete response, residual lesion area ≤ 4 cm2, and tumor located in the mid-rectum were associated with pathologic complete response (ypT0N0).

Almost half of the patients who had a pathologic complete response did not achieve an endoluminal complete response. Tumors located in the mid-rectum with a residual size of ≤ 4 cm2 and the presence of endoluminal complete response were significantly associated with the achievement of ypT0N0.