Anatomical distribution of residual cancer in patients with oesophageal squamous cell carcinoma who achieved clinically complete response after neoadjuvant chemoradiotherapy

Recent advances in neoadjuvant chemoradiotherapy (nCRT) have significantly increased the rates of pathological complete response achieved by patients with oesophageal cancer. Consequently, a watchful waiting strategy based on 'active endoscopic surveillance and surgery as needed' has been proposed for cases without clinical evidence of disease after neoadjuvant chemoradiotherapy. Here, we investigated whether endoscopic surveillance is a reliable tool for the detection of the initially unidentified residual cancer in this patient group.We performed a careful pathological re-review of all cases with oesophageal squamous cell carcinoma, who attained a clinical complete response, despite showing a pathological non-complete response. The detailed anatomical locations of such unidentified malignancies were investigated in each patient to determine the prevalence of cancer involvement for each oesophageal layer.Among the 73 patients with clinical complete response, 46 (63%) patients were found to have pathological non-complete response. The majority (89.1%; n = 41) of patients had evidence of residual cancer in the oesophagus, whereas only 5 (10.9%) patients had T0N+ disease. However, a high percentage (39.1%; n = 16) of patients had no detectable cancer in the mucosa and 9 of them also had no detectable cancer in sub-mucosal layer, ultimately hampering their detection via endoscopic biopsy.Nearly 40% of patients with oesophageal squamous cell carcinoma who attained clinical complete response but showed a pathological non-complete response had residual cancer hidden underneath a cancer-free mucosa layer.