Nuclear magnetic resonance with diffusion: a new alternative to measure pathologic response to neoadjuvant therapy for rectal cancer

Background: There exist clinical-pathological discrepancies at the staging after neoadyuvant therapy of rectal cancer, and there are currently no additional useful methods to distinguish the presence or absence of viable tumor. Objective: To determine the value of magnetic resonance diffusion imaging technique in the identification of the pathological complete response after the neoadyuvant therapy and to determine its relationship with the degree of clinical response. Setting: Private Community Hospital. Design: Retrospective Population: 24 patients (10 women), median age: 61, operated on for rectal cancer from June 2009 to January 2011. Outcome measures: According to the clinical response, patients grouped in responders and non-responders. All apparent diffusion coefficient value greater than 1.2x10-3 mm2/seg was regarded as pathological response. Results: Median of apparent diffusion coefficient was 1.1 (0.7 and 2 range). In 4 cases (17 per cent) the apparent diffusion coefficient was greater than 1.2x10-3 mm2, and were regarded as pathological complete. The median of apparent diffusion coefficient in cases with complete pathological response was significantly higher than the cases without pathological complete response (1.45 vs 1.01 respectively, p 0.0002). Five out of 24 patients (21%) corresponded to the group in clinical response. Of these, 4 were n pathological compete response. The magnetic resonance imaging technique was able to identify these 4 cases. In the patient of this group which featured tumor persistence, the apparent diffusion coefficient value was 1.1. Thus the magnetic resonance diffusion imaging technique was able to identify the only case in which a radical surgery would be justified. Among the 19 patients were considered non-responders, none had pathological complete response. In all these cases apparent diffusion coefficient rates were lower to 1.2x10-3 mm2/sec and therefore there was no case of false negative. Conclusions: The magnetic resonance diffusion technique is a useful tool for the staging after neoayuvant therapy in rectal cancer. (authors)