Most cancers are classified into five stages, numbered 0 through IV (4). The higher the number, the larger the tumor and the more it has spread through the body. This system applies to the majority of solid tumors, though some cancers, particularly blood cancers, use different frameworks entirely.
The Five Standard Stages
Stage 0: Abnormal cells are present but have not spread into nearby tissue. This is also called carcinoma in situ. Stage 0 is not technically cancer yet, but it can become cancer if left untreated.
Stage I: Cancer is present and confined to a small area. The tumor is relatively small and has not grown deeply into surrounding tissues or reached the lymph nodes.
Stage II and Stage III: The cancer is larger and has grown more deeply into nearby tissue. It may also have spread to lymph nodes near the original tumor, but not to distant parts of the body. The distinction between II and III generally comes down to tumor size and how many lymph nodes are involved.
Stage IV: The cancer has spread to distant organs or tissues far from where it started. This is also called metastatic cancer. A breast cancer that has spread to the bones or lungs, for example, would be stage IV.
How Doctors Determine the Stage
Staging relies on a system called TNM, maintained by the American Joint Committee on Cancer (AJCC). Each letter captures a different dimension of the cancer:
- T (Tumor): The size and extent of the primary tumor, rated T1 through T4. Higher numbers mean a larger tumor or deeper growth into surrounding tissue.
- N (Nodes): Whether cancer has reached nearby lymph nodes, rated N0 (no lymph node involvement) through N3. Higher numbers mean more lymph nodes contain cancer cells.
- M (Metastasis): Whether cancer has spread to distant parts of the body. M0 means it hasn’t; M1 means it has.
A cancer described as T1N0M0, for instance, is a small tumor with no lymph node involvement and no distant spread. That combination would typically correspond to stage I. A cancer labeled T3N1M0 is larger, involves some lymph nodes, but still hasn’t spread to distant organs, likely placing it in stage II or III depending on the specific cancer type. Doctors combine these three values to assign one of the five overall stages.
These T, N, and M values can be further subdivided. You might see T3a or T3b on a pathology report, which provides even finer detail about how the tumor has grown. The subcategories vary by cancer type.
Clinical Staging vs. Pathological Staging
You may receive a stage at two different points. Clinical staging happens before surgery, based on physical exams, imaging, and biopsy results. Pathological staging happens after surgery, when a pathologist examines the actual tumor tissue and any lymph nodes that were removed. The pathological stage is generally more precise because it’s based on direct observation of the tissue rather than imaging alone.
Sometimes the two don’t match. A tumor that appeared to be stage II on a scan might turn out to be stage III once the surgeon removes it and a pathologist counts how many lymph nodes are involved. The pathological stage typically takes priority in guiding treatment decisions going forward.
Stage Is Not the Same as Grade
Stage and grade are two different things, and they’re easy to confuse. Stage describes how far the cancer has spread through your body. Grade describes how abnormal the cancer cells look under a microscope, which indicates how aggressively they’re likely to grow. A low-grade cancer has cells that still look somewhat normal and tend to grow slowly. A high-grade cancer has cells that look very abnormal and typically grow faster.
You can have a low-stage, high-grade cancer (small but aggressive) or a high-stage, low-grade cancer (widespread but slow-growing). Both pieces of information matter for treatment planning.
Cancers That Use Different Systems
Not every cancer fits neatly into the 0-through-IV framework. Blood cancers like leukemia don’t form solid tumors, so the TNM system doesn’t apply. Chronic lymphocytic leukemia, for example, uses two separate systems: the Rai system (more common in the United States) and the Binet system (more common in Europe). These are based largely on blood test results and physical findings rather than tumor size or spread.
Lymphomas use yet another approach called the Lugano classification, a modified version of the older Ann Arbor system. Brain cancers, too, are often graded rather than staged in the traditional sense, because they rarely spread outside the brain.
So while “five stages, 0 through IV” is the correct general answer, the staging system your doctor uses will depend on the specific type of cancer involved. The overall logic is the same across all of them: lower numbers mean the disease is more contained, and higher numbers mean it has spread further.
Why Staging Matters
Stage is one of the most important factors in choosing treatment. Early-stage cancers (stages I and II) are more likely to be treated with surgery alone or surgery plus a short course of additional therapy. Later-stage cancers (stages III and IV) typically require more aggressive or combination approaches.
Stage also provides a general sense of prognosis. Survival statistics are often reported by stage, which is why it’s one of the first things an oncologist determines after diagnosis. It’s worth knowing that a cancer’s stage is usually set at the time of diagnosis and doesn’t change, even if the cancer later grows or shrinks with treatment. If a stage II cancer returns after treatment and spreads to distant organs, it’s described as “recurrent” rather than being re-staged as stage IV.