Localized (code = 1)
A localized cancer is a malignancy limited to the organ of origin; it has spread no farther than the organ in which it started. There is infiltration past the basement membrane of the epithelium into the functional part of the organ, but there is no spread beyond the boundaries of the organ. A tumor can be widely invasive or even show metastases within the organ itself and still be considered "confined to organ of origin," or localized, in summary stage.
The illustration below shows a tumor that has invaded past the basement membrane below the surface epithelium of the organ into the parenchyma or stroma.
As previously mentioned, an in situ diagnosis can only be made microscopically, because a pathologist must identify the basement membrane and determine that it has not been penetrated. If the basement membrane has been disrupted or invaded, the case is no longer in situ and is at least localized.
It is important to know and recognize the names of different structures within the organ (such as lamina propria , myometrium, muscularis propria, for example) so that a description of invasion or involvement of these structures will not be interpreted as regional spread.
Because summary stage uses both clinical and pathologic information, it is important to read the pathology and operative report(s) for comments on gross evidence of spread, microscopic extension and metastases, as well as diagnostic imaging reports for mention of distant disease. If any of these reports provides evidence that the cancer has spread beyond the boundaries of the organ of origin, the case is not localized. On the other hand, if the pathology reports, operative reports and other investigations show no evidence of spread, the tumor may be assumed to be localized (as long as in situ has been eliminated as a possibility).