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Cancer Grade vs. Cancer Stage

Doctors use diagnostic tests like biopsies and imaging exams to determine a cancer's grade and its stage. While grading and staging help doctors and patients understand how serious a cancer is and form a treatment plan, they measure two different aspects of the disease.

What is a cancer grade?

A cancer’s grade describes how abnormal the cancer cells and tissue look under a microscope when compared to healthy cells. Cancer cells that look and organize most like healthy cells and tissue are low grade tumors. Doctors describe these cancers as being well differentiated. Lower grade cancers are typically less aggressive and have a better prognosis.

The more abnormal the cells look and organize themselves, the higher the cancer’s grade. Cancer cells with high grades tend to be more aggressive. They are called poorly differentiated or undifferentiated.

Some cancers have their own system for grading tumors. Many others use a standard 1-4 grading scale.

Grade 1: Tumor cells and tissue looks most like healthy cells and tissue. These are called well-differentiated tumors and are considered low grade.
Grade 2: The cells and tissue are somewhat abnormal and are called moderately differentiated. These are intermediate grade tumors.
Grade 3: Cancer cells and tissue look very abnormal. These cancers are considered poorly differentiated, since they no longer have an architectural structure or pattern. Grade 3 tumors are considered high grade.
Grade 4: These undifferentiated cancers have the most abnormal looking cells. These are the highest grade and typically grow and spread faster than lower grade tumors.

What is a cancer stage?

While a grade describes the appearance of cancer cells and tissue, a cancer’s stage explains how large the primary tumor is and how far the cancer has spread in the patient’s body.

There are several different staging systems. Many of these have been created for specific kinds of cancers. Others can be used to describe several types of cancer.

Stage 0 to stage IV

One common system that many people are aware of puts cancer on a scale of 0 to IV.

Stage 0 is for abnormal cells that haven’t spread and are not considered cancer, though they could become cancerous in the future. This stage is also called “in-situ.”
Stage I through Stage III are for cancers that haven’t spread beyond the primary tumor site or have only spread to nearby tissue. The higher the stage number, the larger the tumor and the more it has spread.
Stage IV cancer has spread to distant areas of the body.

TNM staging

Another common staging tool is the TNM system, which stands for Tumor, Node, Metastasis. When a patient’s cancer is staged with TNM, a number will follow each letter. This number signifies the extent of the disease in each category. According to the National Cancer Institute and MD Anderson experts, the standard TNM system uses the following rules:

Primary tumor (T)

TX: Main tumor cannot be measured.
T0: Main tumor cannot be found.
T(is), or T in situ: The tumor is still within the confines of the normal glands and cannot metastasize.
T1, T2, T3, T4: Refers to the size and/or extent of the main tumor. The higher the number after the T, the larger the tumor or the more it has grown into nearby tissues. T's may be further divided to provide more detail, such as T3a and T3b.

Regional lymph nodes (N)

Lymphatic fluid transports immune system cells throughout the body. Lymph nodes are small bean-shaped structures that help move this fluid. Cancer often first spreads to and through nearby lymph nodes.

NX: Cancer in nearby lymph nodes cannot be measured.
N0: There is no cancer in nearby lymph nodes.
N1, N2, N3: Refers to the number and location of lymph nodes that contain cancer. The higher the number after the N, the more lymph nodes that contain cancer.

Distant metastasis (M)

Metastasis is the spread of cancer to other parts of the body.