What defines an in situ tumor?

An in situ tumor is specifically defined as a tumor that has not yet invaded nearby surrounding tissues. This means that the cancerous cells are present in the original site where they formed but have not breached the basement membrane to spread into adjacent areas. In situ tumors can often be detected through screening and have a better prognosis due to their localized nature.

The distinction is crucial in terms of treatment management and prognosis, as in situ tumors typically represent an early stage of cancer, where intervention can lead to effective treatment outcomes. Understanding this definition is important for tumor registrars and healthcare providers in correctly categorizing tumor stages and determining the appropriate clinical approach.