Defining response to radiotherapy in rectal cancer using magnetic resonance imaging and histopathological scales

Aim: To define good and poor regression using pathology and MRI regression scales after neo-adjuvant chemotherapy for rectal cancer. Methods: A systematic review of all studies up to December 2015, without language restriction that were identified from MEDLINE, Cochrane Controlled Trials Register (1960–2015), and EMBASE (1991–2015). Searches were performed of article bibliographies and conference abstracts. MeSH and text words, included “tumour regression”, “mrTRG”, “poor response” and “colorectal cancers”. Clinical studies using either MRI or histopathological TRG scales to define good and poor responders were included in relation to outcomes (local (LR), distant recurrence (DR), disease free (DFS), overall survival (OS)). There was no age restriction to included patients nor stage of cancer.Data was extracted by two authors independently using pre-defined outcome measures. Results: Quantitative data (prevalence) were extracted and analysed according to meta-analytical techniques using comprehensive meta-analysis. Qualitative data (LR, DR, DFS &OS) were presented as ranges. The overall proportion of poor responders after neo-adjuvant CRT was 37.7% (CI: 30.1 to 45.8). There were 19 different reported histopathological scales and one MRI regression scale (mrTRG). Clinical studies used nine and six histopathological scales for poor and good responders respectively. All studies using MRI to define good and poor response used one scale. The most common histopathological definition for good response was the Mandard grades 1&2 or Dworak grades 3&4; Mandard 3,4&5 and Dworak 0,1&2 were used for poor response. For histopathological grades, the 5-year outcomes for poor responders were LR 3.4-4.3%, DR 14.3-20.3%, DFS 61.7-68.1% and OS 60.7-69.1. Good pathological response 5-year outcomes were LR, 0-1.8%; DR, 0-11.6%; DFS, 78.4-86.7%; and, OS, 77.4-88.2%. A poor response on MRI (mrTRG 4,5) resulted in 5-year LR 4-29%, DR 9%, DFS 31-59% and OS 27-68%. The 5-year outcomes with a good response on MRI (mrTRG 1,2 & 3) was LR 1-14%, DR 3%, DFS 64-83% and OS 72-90%. Conclusions: For histopathology regression assessment Mandard1,2/Dworak3,4 should be used for good and Mandard3,4,5/Dworak0,1,2 for poor response. MRI indicates good and poor response by mrTRG1-3 and mrTRG4-5 respectively.