title: Fragmented pattern of tumor regression and lateral intramural spread may influence margin appropriateness after TEM for rectal cancer following neoadjuvant CRT.
abstract: BACKGROUND
  The main tenets of local excision of rectal cancer following neoadjuvant chemoradiation (CRT) are that the mucosal scar represents the main focus of residual disease and a solid conglomerate around this rather than being scattered (fragmented) through the bowel wall.
  
  
  METHODS
  Retrospective review of a prospective cohort of patients with residual rectal ycT1-2N0 adenocarcinoma with small residual tumors (≤3 cm) following CRT who underwent transanal endoscopic microsurgery (TEM) with 1-cm margins around the residual mucosal abnormality was performed. Distribution and morphology (solid vs. fragmented) of tumor spread were studied and correlated to postoperative oncological outcomes.
  
  
  RESULTS
  Thirty patients were included. Twenty percent (n = 6) were ypT1, 60% (n = 18) were ypT2, and 20% (n = 6) were ypT3 tumors. Fragmentation was present in 37%. The mean distance between foci of residual scattered tumor was 3.6 ± 2.0 mm. Lateral spread under normal mucosa was present in 19 specimens (53%; mean extension 4.8 ± 2.4 mm). With a median follow up of 32 months, none of these findings impacted upon development of recurrence.
  
  
  CONCLUSIONS
  Both occult lateral spread and fragmented tumor patterns are common findings after CRT. Despite the potential of occult spread to mislead surgeon choice of resection margin, its presence did not influence oncological outcome in this series.
authors.affiliation: Angelita & Joaquim Gama Institute, São Paulo, Brazil; Colorectal Surgery Division, University of São Paulo School of Medicine, São Paulo, Brazil; Ludwig Institute for Cancer Research, São Paulo, Brazil.
authors.forename: Rodrigo O
authors.initials: RO
authors.lastname: Perez
authors.forename: Angelita
authors.initials: A
authors.lastname: Habr-Gama
authors.forename: Fraser M
authors.initials: FM
authors.lastname: Smith
authors.forename: Lauren
authors.initials: L
authors.lastname: Kosinski
authors.forename: Guilherme P
authors.initials: GP
authors.lastname: São Julião
authors.forename: Esteban
authors.initials: E
authors.lastname: Grzona
authors.forename: Viviane
authors.initials: V
authors.lastname: Rawet
authors.forename: Maria Regina
authors.initials: MR
authors.lastname: Vianna
authors.forename: Igor
authors.initials: I
authors.lastname: Proscurshim
authors.forename: Patrício Bernardo
authors.initials: PB
authors.lastname: Lynn
authors.forename: Joaquim
authors.initials: J
authors.lastname: Gama-Rodrigues
mesh_terms: D000230:Adenocarcinoma / Q000473:pathology* / Q000628:therapy; D001003:Anal Canal / Q000601:surgery; D059248:Chemoradiotherapy / Q000009:adverse effects*; D003131:Combined Modality Therapy; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008866:Microsurgery / Q000009:adverse effects*; D008875:Middle Aged; D057605:Natural Orifice Endoscopic Surgery / Q000009:adverse effects*; D020360:Neoadjuvant Therapy / Q000009:adverse effects*; D009361:Neoplasm Invasiveness; D009367:Neoplasm Staging; D018365:Neoplasm, Residual / Q000473:pathology* / Q000628:therapy; D011379:Prognosis; D011446:Prospective Studies; D012004:Rectal Neoplasms / Q000473:pathology* / Q000628:therapy; D012189:Retrospective Studies
keywords: downstaging patterns; neoadjuvant therapy; rectal neoplasms; transanal endoscopic microsurgery