What’s the Difference Between Cancer Grade and Cancer Stage?

October 18, 2019

  • The grade of a tumor is an indication of how abnormal the cancer cells appear under the microscope.
  • The stage of a solid tumor refers to its size and/or whether or not it has spread.

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.

An illustration of a cancer cell.

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.

Learn more about cancer treatment from Dana-Farber Cancer Institute.