What is staging and grading of cancer?
Staging of a cancer is the method of establishing the extent or severity of the cancer and its spread in the body. Staging considers factors like the primary tumor location, tumor size, lymph node involvement and presence of metastasis. Staging is done by an oncologist in conjunction with the radiologist and pathologist after the diagnosis has been confirmed.
Grading of a tumor is a system of classification of cancer cells in a tumor, based on how abnormal the cancer cells appear microscopically, the invasive nature of the tumor, deviations in the rate of growth and potential to spread. The tumor grading is done by a pathologist after specimen tissue is available (usually available after biopsy or surgical excision of the tumor) for microscopic examination and its significance varies with each type of cancer.
Reasons for Staging and Grading
The staging and grading of a tumor will help the doctor with the following :
- to ascertain how far the cancer has progressed
- to plan the appropriate treatment
- to establish the most likely prognosis (outcome of treatment)
- to assist with communication about the severity of cancer between health care professionals
- it may also help in identifying clinical trial programs that may be worth considering for the patient
In general, a low grade cancer or early stage cancer would mean a better prognosis, while a high grade tumor or late stage cancer would suggest a poor prognosis.
Grading plays a significant role in assessing certain types of cancers, like brain tumors, lymphomas, soft tissue cancers (sarcoma), breast and prostate cancer while staging is important for the management of most types of cancers.
Common Factors Assessed in Staging or Grading
Factors commonly assessed in staging are the primary tumor site, tumor size and number of tumors, lymph node spread, cell type and tumor grade and the presence or absence of metastasis. In some type of cancers, other factors are also considered for staging, like ulceration status or tumor thickness in melanoma; staging of cancers of the brain according to the cell type and grade.
Many factors are considered while determining tumor grade. This includes differentiation (assessing the extent that tumor cells differ from the normal cells of the tissue they have originated from), deviations in the rate of growth, growth pattern, size and shape of the nucleus in tumor cells and the percentage of tumor cells that are dividing, and the degree of invasiveness. The specific factors used to determine tumor grade can vary with different types of cancers.
Procedures for Staging or Grading
Staging is conducted by performing various tests and procedures and assessing the results of the following :
- physical examination
- radiological studies like x-rays, CT, MRI, or PET scans can show the cancer location, tumor size, and whether it has metastasized
- laboratory tests including analysis of blood, urine, other fluids, tumor markers and tissue taken from the body
- pathological reports like studies of lymph nodes and biopsied/excised tissues
- surgical reports like the size and extension of tumor as observed in surgery
A staging done without pathological evaluation is called clinical staging while, the staging done after surgical procedure or exploration and subsequent pathologic evaluation is known as pathologic staging.
Grading is done by detailed microscopic examination of multiple sections of the various tissues obtained from biopsy or surgical excision of the tumor from the patient.
Common Staging and Grading Systems
The TNM system is the most commonly used and widely accepted system for staging. It is based on the :
- extent of the tumor (T)
- lymph node spread (N)
- presence of distant metastasis (M)
What does T in the TNM cancer staging mean?
The tumor ‘T’ is numbered as T1, T2, T3 and T4 based on the size and extent of tumor. T1 denotes small sized tumors, T4 stands for the largest, and intermediate sized tumors are indicated by T2 and T3.
The categorization is based on specific criteria for each cancer. Tx is used when primary tumor cannot be evaluated, T0 is used when there is no evidence of tumor and Tis is used for tumor in situ (cancer cells present but confined to tissue of origin).
What does N in the TNM cancer staging mean?
Similarly lymph node ‘N’ is numbered N1, N2 and N3 depending on the number of lymph node involvement or extent. N0 is used when there is no evidence of lymph node spread and Nx is used when it cannot be evaluated.
What does M in the TNM cancer staging mean?
M1 is used when distant metastasis is present, M0 when it is absent and Mx when it cannot be evaluated.
Cancer Stages 0, 1, 2, 3, 4
Cancer is classified into five stages from stage 0 to stage IV, based on various TNM combinations, for most of the cancers. Stage 0 represents carcinoma in situ and stage IV represents advanced or metastatic cancer. Stage I to III denotes progressive increase in the size of the tumor size and lymph node involvement. In general, the lower the stage at the time of diagnosis, the better the prognosis.
TNM staging is not applicable to hematological cancers. Different staging systems are used for many cancers of the blood, lymphoid tissue or bone marrow. The AJCC adopted staging for lymphoma is the Ann Arbor staging classification.
Cancer Grading Systems
Common grading systems categorize the tumor into various grades ranging from grade 1 to grade 4. Grade 1 (low grade) tumors are well differentiated (resemble normal cells) and are less aggressive, while the grade 4 (high grade) tumors are poorly differentiated and notoriously aggressive.
The AJCC recommended tumor grading system has G1, G2, G3 and G4 (representing grade 1 to 4) and Gx for denoting undetermined grade. Grading systems may be different for different type of cancers. For example, in prostate cancer the Gleason score is commonly used and the Fuhrman system may be used for kidney cancer.
Problems with Staging and Grading
Different cancers will have different criteria for staging and grading. Tumor grading, which is based on the pathologist’s assessment may be open to inaccuracies. A sampling error can result in sending inadequate or inappropriate tissue for examination as the tissue biopsied may not be the most malignant representative of the cancerous cells. Cancer cells can become more aggressive with time and can result in progression of the grade and stage. The correlation between microscopic appearance and biologic behavior is not flawless.
Meaning of Staging and Grading
A lower stage cancer would mean there is a better chance for treatment (surgery, radiotherapy, chemotherapy). With increasing stages the complexity of treatment increases and chances of relapse increases.
A stage IV would mean the chances of surgical removal is minimal and chemotherapy/targeted therapy would become the main therapeutic option. Therapeutic surgery may still be done in selected patients in stage IV while palliative surgeries may be done in late stages to improve quality of life.
A low grade cancer can be treated more conservatively and followed-up less aggressively, with lower chance of recurrence compared to very aggressive treatment and follow-up approaches adopted in high grade tumors with higher chances of recurrence.
This article serves as a guide to the staging and grading systems. Always speak to a medical doctor or oncologist before making any decision regarding the treatment of cancer.