title: Tumor scatter after neoadjuvant therapy for rectal cancer:  are we dealing with an invisible margin?
abstract: BACKGROUND
  After the impressive response of rectal cancers to neoadjuvant therapy, it seems reasonable to ask: can we can excise the small ulcer locally or avoid a radical resection if there is no gross residual tumor? Does gross response reflect what happens to tumor cells microscopically after radiation?
  
  
  OBJECTIVE
  The aim of this study was to identify microscopic tumor cell response to radiation.
  
  
  METHODS
  This study is a retrospective review of a prospectively collected database.
  
  
  METHODS
  This investigation was conducted at a single tertiary medical center.
  
  
  METHODS
  Patients were selected who had elective radical resection for rectal cancer after preoperative chemotherapy and radiation performed by 2 colorectal surgeons between 2006 and 2011.
  
  
  METHODS
  The primary outcome measured was tumor presence after radiation therapy
  
  
  RESULTS
  Of the 75 patients, 20 patients were complete responders and 55 had residual cancer. Of these patients, 28 had no tumor cells seen outside the gross ulcer, and 27 (49.1%) had tumor outside the visible ulcer or microscopic tumor present with no overlying ulcer. Of these tumors, 81.5% were skewed away from the ulcer center. The mean distance of distal scatter was 1.0 cm from the visible ulcer edge to a maximum of 3 cm; 3 patients had tumor cells more than 2 cm distal to the visible ulcer edge. Tumor scatter outside the ulcer was not associated with poor prognostic factors, such as nodal and distant disease, perineural invasion, or mucin; however, it was associated with lymphovascular invasion (χ2 = 4.12, p = 0.038)
  
  
  CONCLUSIONS
  There was limited access to clinical information gathered outside our institution.
  
  
  CONCLUSIONS
  Our study suggests that 1) after radiation, the gross ulcer cannot be used to determine the sole area of potential residual tumor, 2) cancer cells may be found up to 3 cm distally from the gross ulcer, so the traditional 2-cm margin may not be adequate, and 3) local excision of the ulcer or no excision after apparent complete response appears to be insufficient treatment for rectal cancer.
authors.affiliation: Department of General Surgery, Section of Colon and Rectal Surgery, Rush University Medical Center, Chicago, Illinois, USA. dhayden21@gmail.com
authors.forename: Dana M
authors.initials: DM
authors.lastname: Hayden
authors.forename: Shriram
authors.initials: S
authors.lastname: Jakate
authors.forename: Maria C Mora
authors.initials: MC
authors.lastname: Pinzon
authors.forename: Deborah
authors.initials: D
authors.lastname: Giusto
authors.forename: Amanda B
authors.initials: AB
authors.lastname: Francescatti
authors.forename: Marc I
authors.initials: MI
authors.lastname: Brand
authors.forename: Theodore J
authors.initials: TJ
authors.lastname: Saclarides
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016009:Chi-Square Distribution; D003131:Combined Modality Therapy; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D020360:Neoadjuvant Therapy; D009361:Neoplasm Invasiveness; D009362:Neoplasm Metastasis; D009367:Neoplasm Staging; D018365:Neoplasm, Residual; D016016:Proportional Hazards Models; D012004:Rectal Neoplasms / Q000473:pathology* / Q000628:therapy*; D012189:Retrospective Studies; D016896:Treatment Outcome