title: Tumour regression in the randomized Stockholm III Trial of radiotherapy regimens for rectal cancer.
abstract: BACKGROUND
  The Stockholm III Trial randomized patients with primary operable rectal cancers to either short-course radiotherapy (RT) with immediate surgery (SRT), short-course RT with surgery delayed 4-8 weeks (SRT-delay) or long-course RT with surgery delayed 4-8 weeks. This preplanned interim analysis examined the pathological outcome of delaying surgery.
  
  
  METHODS
  Patients randomized to the SRT and SRT-delay arms in the Stockholm III Trial between October 1998 and November 2010 were included, and data were collected in a prospective register. Additional data regarding tumour regression grade, according to Dworak, and circumferential margin were obtained by reassessment of histopathological slides.
  
  
  RESULTS
  A total of 462 of 545 randomized patients had specimens available for reassessment. Patients randomized to SRT-delay had earlier ypT categories, and a higher rate of pathological complete responses (11·8 versus 1·7 per cent; P = 0·001) and Dworak grade 4 tumour regression (10·1 versus 1·7 per cent; P < 0·001) than patients randomized to SRT without delay. Positive circumferential resection margins were uncommon (6·3 per cent) and rates did not differ between the two treatment arms.
  
  
  CONCLUSIONS
  Short-course RT induces tumour downstaging if surgery is performed after an interval of 4-8 weeks.
authors.affiliation: Departments of Molecular Medicine and Surgery, Karolinska Institute, Stockholm, Sweden.
authors.forename: D
authors.initials: D
authors.lastname: Pettersson
authors.affiliation: Departments of Oncology and Pathology, Karolinska Institute, Stockholm, Sweden.
authors.forename: E
authors.initials: E
authors.lastname: Lörinc
authors.affiliation: Departments of Molecular Medicine and Surgery, Karolinska Institute, Stockholm, Sweden.
authors.forename: T
authors.initials: T
authors.lastname: Holm
authors.affiliation: Departments of Molecular Medicine and Surgery, Karolinska Institute, Stockholm, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Iversen
authors.affiliation: Departments of Molecular Medicine and Surgery, Karolinska Institute, Stockholm, Sweden.
authors.forename: B
authors.initials: B
authors.lastname: Cedermark
authors.affiliation: Departments of Oncology and Pathology, Karolinska Institute, Stockholm, Sweden.|Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
authors.forename: B
authors.initials: B
authors.lastname: Glimelius
authors.affiliation: Departments of Molecular Medicine and Surgery, Karolinska Institute, Stockholm, Sweden.
authors.forename: A
authors.initials: A
authors.lastname: Martling
mesh_terms: D000230:Adenocarcinoma / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D011300:Preoperative Care; D011446:Prospective Studies; D018714:Radiotherapy, Adjuvant; D012004:Rectal Neoplasms / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery*; D013997:Time Factors