Assessing pathological complete response to neoadjuvant chemoradiotherapy in locally advanced rectal cancer: a systematic review

Aim Pathological complete response to neoadjuvant chemoradiotherapy is found in 20% of patients with rectal cancer undergoing long-course chemoradiotherapy. Some authors have suggested that these patients do not need to undergo surgery and can be managed with careful follow-up, with surgery only used in the event of clinical failure. Widespread adoption of this regimen is limited by the accuracy of methods to confirm a pathological complete response (pCR). Method A systematic search of PubMed, Medline and Cochrane databases was conducted to identify clinical, histological and radiological features in those patients with rectal cancer who achieved a pCR following chemoradiotherapy. Searches were conducted with the following keywords and MeSH search terms: 'rectal neoplasm', 'response', 'neoadjuvant', 'preoperative chemoradiation' and 'tumour response'. After review of title and abstracts, 89 articles addressing the assessment of pCR were identified. Results Histology and clinical assessment are the most effective methods of assessment of pCR, with histology considered the gold standard. Clinical assessment is limited to low rectal tumours and is open to significant inter-rater variability, while histological examination requires a surgical specimen. Diffusion-weighted MRI and 18 F-fluorodeoxyglucose positron emission tomography/CT demonstrate the greatest potential for the assessment of pCR, but both modalities have limited accuracy. Conclusion Determination of a pCR is crucial if a non-operative approach is to be undertaken proactively. Various methods are available, but currently they lack sufficient sensitivity and specificity to define management. This is likely to be an area of further research in the future.