What is the Difference Between Cancer Grade and Cancer Stage?
Why is Cancer Grading and Staging Needed?
Cancer Grade and Cancer Stage
Doctors use diagnostic tests like biopsies and imaging exams to determine cancer‘s grade and its stage. The stage of a cancer describes the size of a tumour and how far it has spread from where it originated. The grade describes the appearance of the cancerous cells.
Staging and grading the cancer will allow the doctors to 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. It is an indicator of how quickly a tumor is likely to grow and spread.
If the cells of the tumor and the organization of the tumor’s tissue are close to those of normal cells and tissue, the tumor is called “well differentiated .”
These tumors tend to grow and spread at a slower rate than tumors that are “undifferentiated” or “poorly differentiated.”
The more abnormal the cells look and lack of normal tissue structures, the higher the cancer’s grade. Cancer cells with a high grades tend to be more aggressive. They are called poorly differentiated or undifferentiated.
Based on these and other differences in microscopic appearance, doctors assign a numerical “grade” to most cancers. The factors used to determine tumor grade can vary between different types of cancer.
Tumor grade is not the same as the stage of a cancer. Cancer stage refers to the size and/or extent (reach) of the original (primary) tumor and whether or not cancer cells have spread in the body.
The cancer stage is based on factors such as the location of the primary tumor, tumor size, regional lymph node involvement (the spread of cancer to nearby lymph nodes), and the number of tumors present.
How is Tumor Grade Determined?
If a tumor is suspected to be malignant, a doctor removes all or part of it during a procedure called a biopsy.
A pathologist (a doctor who identifies diseases by studying cells and tissues under a microscope) then examines the biopsied tissue to determine whether the tumor is benign or malignant. The pathologist also determines the tumor’s grade and identifies other characteristics of the tumor.
How are Tumor Grades Classified?
Grading systems differ depending on the type of cancer. In general, tumors are graded as 1, 2, 3, or 4, depending on the amount of abnormality
If a grading system for a tumor type is not specified, the following 1-4 grading scale is generally used :
- GX: Grade cannot be assessed (undetermined grade)
- Grade 1 Well differentiated(low grade): Tumor cells and tissue looks most like healthy cells and tissue. These are called well-differentiated tumors and are considered low grade.
- Grade 2 Moderately differentiated (intermediate grade): The cells and tissue are somewhat abnormal and are called moderately differentiated. These are intermediate grade tumors.
- Grade 3 Poorly differentiated (high grade): 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 Undifferentiated (high grade): 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.
1. Clinical Staging
The clinical stage is an estimate of the extent of the cancer based on results of physical exams, imaging tests (x-rays, CT scans, etc.), endoscopy exams, and any biopsies that are done before treatment starts. For some cancers, the results of other tests, such as blood tests, are also used in clinical staging.
The clinical stage is often a key part of deciding the best treatment options. It can also be used when trying to get an idea of what a person’s outlook (prognosis) might be. For example, the survival rates for most types of cancer are based mainly on the stage at the time of diagnosis (see below).
2. Pathological Staging (Surgical Staging)
If surgery to remove the cancer is the first treatment, doctors can also determine the pathological stage (also called the surgical stage). The pathological stage relies on the results of the exams and tests done before the surgery, as well as what is learned about the cancer during surgery.
Sometimes, the surgical stage is different from the clinical stage (for instance, if the surgery shows the cancer has spread more than was seen on imaging tests).
The pathological stage gives more precise information, which can be used to help determine what other treatments might be needed, as well as to help predict treatment response and outcomes (prognosis).
3. Post-Neoadjuvant Therapy (or Post Therapy) Staging
For some cancers, some treatment other than surgery (such as chemo, targeted drug therapy, or radiation) might be done first.
The goal might be to try to shrink the tumor before surgery (in which case the treatment is called neoadjuvant therapy), or it might be done as the main treatment if it’s not clear that surgery is going to be an option.
Staging might be done after this first treatment to help measure the cancer’s response to treatment. This can be done the same way as clinical staging (if surgery hasn’t been done yet), which can help determine what type of surgery should be done. Or it can be done after surgery (the same way as pathological staging), which might give more precise information.
4. Recurrence or Retreatment Staging
Staging might also be done again at some point if the cancer comes back (recurs) or progresses (grows or spreads without ever having gone away completely). This information can be used to help guide decisions about further treatment.
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. This stage describes cancer in situ, which means “in place.” Stage 0 cancers are still located in the place they started and have not spread to nearby tissues. This stage of cancer is often highly curable, usually by removing the entire tumor with surgery.
- Stage I. This stage is usually a small cancer or tumor that has not grown deeply into nearby tissues. It also has not spread to the lymph nodes or other parts of the body. It is often called early-stage cancer.
- Stage II and Stage III. In general, these 2 stages indicate larger cancers or tumors that have grown more deeply into nearby tissue. They may have also spread to lymph nodes but not to other parts of the body.
- Stage IV. This stage means that the cancer has spread to other organs or parts of the body. It may also be called advanced or metastatic cancer.
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.
The standard TNM system uses the following rules:
1. Primary Tumor (T)
- TX: The main tumor cannot be measured.
- T0: The 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.
2. 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.
3. Distant Metastasis (M)
Metastasis is the spread of cancer to other parts of the body.
- MX: Metastasis cannot be measured.
- M0: Cancer has not spread to other parts of the body.
- M1: Cancer has spread to other parts of the body.
4. Other Notations That Can Be Part of TNM
Each of the T, N, and M categories might be written with a lowercase letter in front of it, showing if it’s a clinical or pathological classification:
- A clinical stage is noted with “c” (for example, cT1)
- A pathological stage is noted with “p” (for example, pN2)
For staging that is done after treatment or after cancer recurrence/progression, a category might also be given another lowercase letter in front of it:
- For cancers that are restaged after neoadjuvant therapy (or other therapy), a “y” might be used in front of the category (for example, ycT1 or ypT2)
- For cancers that are restaged after recurrence or progression of the cancer, an “r” might be used in front of the category (for example, rcT1 or rpT2)
Why is Cancer Grading Needed?
Doctors use tumor grade and other factors, such as cancer stage and a patient’s age and general health, to develop a treatment plan and to determine a patient’s prognosis (the likely outcome or course of a disease; the chance of recovery or recurrence).
Generally, a lower grade indicates a better prognosis. A higher grade cancer may grow and spread more quickly and may require immediate or more aggressive treatment.
The importance of tumor grade in planning treatment and determining a patient’s prognosis is greater for certain types of cancer, such as soft tissue sarcoma, primary brain tumors, and breast and prostate cancer.
Why is Cancer Staging Needed?
For most types of cancer, doctors need to know how much cancer there is and where it is (among other things) to help determine the best treatment options.
For example, the best treatment for an early stage cancer may be surgery or radiation, while a more advanced-stage cancer may need treatments that reach all parts of the body, such as chemotherapy, targeted drug therapy, or immunotherapy.
Of course, the stage of a cancer isn’t the only factor used to decide which treatments might be best. Sometimes, cancers with different stages might be treated the same way, or cancers with the same stage might be treated in different ways. Many factors determine the best treatment options for each person.
A cancer’s stage can also be used to help predict the course it will likely take, as well as how likely it is that treatment will be successful. Although each person’s situation is different, cancers of the same type and stage tend to have similar outlooks.
The cancer stage is also a way for doctors to describe the extent of the cancer when they talk with each other about a person’s cancer.
Not all cancers are staged. For example, leukemias are cancers of the blood cells and therefore typically have spread throughout the body by the time they are found. Most types of leukemias aren’t staged the way cancers that form tumors are.