Colon (tumor & nontumor)
Posttreatment changes

Topic Completed: 1 December 2015

Minor changes: 31 July 2020

Copyright: 2002-2019,, Inc.

PubMed Search: "Post treatment" "rectal carcinoma"

Raul S. Gonzalez, M.D.
Page views in 2019: 971
Page views in 2020 to date: 804
Cite this page: Gonzalez R. Posttreatment changes. website. Accessed August 6th, 2020.
Essential features
  • Rectal tumors often receive neoadjuvant treatment before resection
  • Microscopic findings include fibrosis and acellular mucin
  • Acellular mucin does not equal viable residual tumor and serial sections to hunt for rare cancer cells are not warranted
  • Rectum only; neoadjuvant treatment is generally not given for colonic carcinoma
Clinical features
  • Treatment often shrinks tumors, reducing risk of local recurrence
  • Patients may experience treatment related complications or anorectal dysfunction (Dis Colon Rectum 2011;54:901)
Gross description
  • Flat, firm mass with central ulceration
  • May be no identifiable lesion
  • Unless residual tumor is grossly obvious, entire lesion site should be submitted for examination
  • Completeness of mesorectal excision should be assessed (J Clin Pathol 2007;60:849)
Microscopic (histologic) description
  • Microscopic changes include fibrosis, acellular mucin, necrotic tumor, ulceration and hemosiderin
  • Viable residual tumor may appear well, moderate or poorly differentiated
  • Lymph node metastases may remain viable, even if entire primary tumor is destroyed; viable tumor deposits also may be seen and portend poor outcome (Mod Pathol 2014;27:1281)
  • Various grading systems exist for tumor response, with poor concordance (Hum Pathol 2012;43:1917)
  • Acellular mucin should not be interpreted as residual tumor (Am J Surg Pathol 2011;35:127)
  • Deeper sections to search for rare residual tumor cells has little bearing on patient outcome (Histopathology 2011;59:650)
Microscopic (histologic) images

Contributed by Raul S. Gonzalez, M.D.
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Various images

Positive stains
  • Cytokeratin may be used to detect rare residual tumor cells
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