The Clinical Impact of MicroRNA-21 in Low Rectal Cancer Treated with High-Dose Chemoradiotherapy in the Organ Preserving Setting

Background: Organ preservation in the treatment of rectal cancer has seen an increase in interest. Clinical complete response (cCR) after high-dose chemoradiotherapy (CRT) allows for non-surgical management (NSM), but the selection of patients is challenging and standard clinical staging insufficient. MicroRNA-21-5p (miR-21) is ubiquitously upregulated in cancer and has been associated with treatment response in rectal cancer treated with standard preoperative CRT. The aim of the present study was to investigate this association in low rectal cancer treated in the NSM setting. Methods: Forty-eight patients from our single-arm phase II trial (NCT00952926) were eligible for analysis. All patients had resectable T2 or T3, N0-N1 low adenocarcinoma and received intensity-modulated radiotherapy plus brachytherapy boost and oral tegafur-uracil. Patients with cCR six weeks after end of treatment assessed by clinical examination, magnetic resonance imaging, and biopsy, were referred to observation and close follow-up. The miR expression in the diagnostic biopsies was measured by qPCR. The relationship between miR-21 expression and cCR was assessed using the Wilcoxon rank-sum test. Results: Thirty-eight patients had cCR after treatment and were allocated to observation while 10 patients had incomplete response and underwent surgery. MicroRNA-21 was successfully analyzed in all samples. The median tumor expression of miR-21 was significantly higher in patients with incomplete response than in those with cCR, 24.3 (95% confidence interval (CI) 17.1-36.8) and 16.6 (95% CI 13.9-21.1), respectively, p = 0.03. Conclusions: The present study adds to the evidence of the clinical impact of miR-21 in rectal cancer treated with CRT. The findings are comparable with results seen in patients treated in the standard preoperative setting and may assist in the selection of patients for an organ preserving approach.