Other factors that can affect the stage
For some cancers, the values for T, N, and M aren’t the only things that determine the stage. Some other factors that may be taken into account include:
Grade: For most cancers, the grade is a measure of how abnormal the cancer cells look under the microscope. This is called differentiation. Grade can be important because cancers with more abnormal-looking cells tend to grow and spread faster.
The grade is usually assigned a number. In low-grade (well-differentiated) cancers, the cancer cells look a lot like cells from normal tissue. In general, these cancers tend to grow slowly. In high-grade (poorly differentiated) cancers, the cancer cells look very different from normal cells. High-grade cancers often tend to grow quickly and have a worse outlook, so they may need different treatments than low-grade cancers. Even when the grade doesn’t affect a cancer’s stage, it may still affect the outlook and/or treatment.
Cell type: Some cancers can be made up of different types of cells. Because the type of cancer cell can affect treatment and outlook, it can be a factor in staging. For example, cancers of the esophagus are mainly either squamous cell cancers or adenocarcinomas. Squamous cell esophageal cancers are staged differently from esophageal adenocarcinomas.
Tumor location: For some cancers, the tumor’s location affects outlook and is taken into account in staging. The stage of cancer of the esophagus, for example, depends on whether the cancer is in the upper, middle, or lower third of the esophagus.
Tumor marker levels: For some cancers, the blood levels of certain substances (called tumor markers) can affect the stage of the cancer. For example, in prostate cancer, the level of prostate-specific antigen (PSA) in the blood is taken into account in assigning a stage.