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 with arrows identifying in situ cancer cell, epithelium of organ, and basement membrane.

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: December 15, 2023