When solid tumors are diagnosed, they are often assigned a grade and a stage. Both factors are key considerations when physicians devise a treatment plan.
Tumors are assigned a grade based on the appearance of their cells under a microscope: Low-grade tumor cells resemble normal cells more closely than high-grade tumor cells do. The grade provides suggestions of how aggressive an individual tumor is, how quickly it is likely to grow and spread. In general, low-grade tumors grow less rapidly and higher-grade tumors grow more rapidly.
Different grading systems are used for different types of cancer. In general, tumors are assigned a grade of 1, 2, or 3 (and occasionally 4), based on how abnormal their cells look under a microscope. Sometimes the term “differentiation” is used to refer to grade. Low-grade tumors are also called “well-differentiated,” with high-grade tumors called “poorly differentiated.” Moderately differentiated tumors fall between low- and high-grade.
The stage of a solid tumor refers to its size or extent and whether or not it has spread to other organs and tissues. The actual number used to describe a tumor stage — 0, I, II, III, or IV — can have a different meaning for different types of cancer. In general, the higher the number, the more advanced the disease is.
Tumor stage is determined by a variety of tests such as X-rays or other imaging tests, laboratory tests, and by other procedures that indicate how far it has spread within the body.
There are a variety of systems for staging solid tumors. The most widely used is the TNM system, which incorporates three criteria: the size and extent of the original, or primary, tumor (designated T); the number of nearby lymph nodes found to contain cancer cells (N); and the presence or absence of metastasis (M).
If you have been diagnosed with cancer, talk with your doctor about its grade, stage, and other matters.