In tumor staging, abnormal cells present but not spread to nearby tissue is classified as stage:

In tumor staging, the classification of "stage 0" denotes that abnormal cells are present, but they have not yet invaded surrounding tissues. This stage is sometimes referred to as carcinoma in situ, meaning that the cancerous cells are still localized and have not started to grow into nearby areas. This characterization is crucial because it indicates that the disease is detected at an early stage, which can lead to a better prognosis and potentially simpler treatment options.

Stages I, II, and III typically indicate progressively more invasive forms of cancer, where abnormal cells have either begun to invade nearby tissue or have spread to regional lymph nodes or other areas of the body. Thus, those stages do not apply in the case where no invasion has occurred, making "stage 0" the appropriate classification for the scenario described.