Code 0: In Situ

  • Translates as “in place”
  • Can only be made microscopically (histologically confirmed)
  • Presence of malignant cells within cell group from which they arose
  • Fulfills pathological criteria for malignancy
  • No invasion of basement membrane
  • No invasion of supporting structures of the organ on which it arose

Pathologists have many ways of describing in situ cancer

  • Intracystic
  • Intraepithelial
  • No penetration of/or below the basement membrane
  • No stromal invasion
  • Non-infiltrating
  • Noninvasive
  • Pre-invasive

Organs and tissues that have no epithelial layer cannot be staged as in situ, since they do not have a basement membrane (e.g., sarcomas). The SS2018 manual lists the Chapters that cannot have in situ (see page 10).

Illustration of an in situ tumor.

Source: Adapted from an illustration by Brian Shellito of Scientific American, as printed in Cancer in Michigan, The Detroit News, Nov. 1-2, 1998.

Updated: September 18, 2018