# CAO/ARO/AIO-94 (German Rectal Cancer Study)

Source: https://onco.cc/trials/cao-aro-aio-94/  
OnCo record `cao-aro-aio-94` (Trial). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

The German rectal trial moved chemoradiation to before surgery: local recurrence halved, more sphincters were saved and toxicity fell, with survival unchanged.

## Summary

CAO/ARO/AIO-94 randomised 823 patients with clinical stage II or III rectal cancer to fluorouracil-based chemoradiation (50.4 Gy) given before or after total mesorectal excision. Five-year local recurrence was 6 percent with preoperative and 13 percent with postoperative treatment; acute and long-term toxicity were lower, and sphincter preservation in low tumours doubled, with no difference in overall survival (Sauer and colleagues, New England Journal of Medicine 2004). Preoperative chemoradiation became the standard for locally advanced rectal cancer.

## Fields

- Kind: Trial
- Status: positive
- Last checked: 2026-09-17
- Tags: radiation-wave4
- Phase: 3
- Setting: Locally advanced rectal cancer: preoperative versus postoperative fluorouracil chemoradiation
- Sponsor: German Rectal Cancer Study Group
- Enrolled: 823
- Result: 5-year local recurrence 6% (preoperative) vs 13% (postoperative); overall survival unchanged.
- Outcomes: Local recurrence at 5 years: Preoperative chemoradiation 6% vs Postoperative chemoradiation 13%
- Replication: Confirmed at eleven years: local recurrence 7.1 against 10.1 percent (p=0.048), with no difference in overall survival or distant metastases.

## Sources

- NEJM 2004: https://doi.org/10.1056/NEJMoa040694
- CAO/ARO/AIO-94 at eleven years (Journal of Clinical Oncology 2012): https://doi.org/10.1200/JCO.2011.40.1836

## Connected records

- cancers: [Colorectal cancer](https://onco.cc/cancers/colorectal/), [Rectal cancer](https://onco.cc/cancers/rectal-cancer/)
- technologies: [IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/)
- drugs: [Fluorouracil (5-FU)](https://onco.cc/drugs/fluorouracil/)
- terms: [Chemoradiation (chemoradiotherapy, CRT)](https://onco.cc/terms/chemoradiation/)
- trials: [CAO/ARO/AIO-12](https://onco.cc/trials/cao-aro-aio-12/), [Dutch TME trial](https://onco.cc/trials/dutch-tme-trial/), [PRODIGE 23](https://onco.cc/trials/prodige-23/), [RAPIDO](https://onco.cc/trials/rapido/), [STELLAR (rectal cancer)](https://onco.cc/trials/stellar-rectal/), [Stockholm III](https://onco.cc/trials/stockholm-iii/)
- key papers: [Sauer 2004: chemoradiotherapy before rather than after surgery for rectal cancer (CAO/ARO/AIO-94)](https://onco.cc/key-papers/paper-sauer-preoperative-chemoradiotherapy-rectal-nejm-2004/)

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