Most cancers are staged using five main stages, numbered 0 through 4. Stage 0 means abnormal cells are present but haven’t spread into nearby tissue. Stage 4 means cancer has spread to distant parts of the body. But the full picture is more nuanced than a single number, and some cancers use entirely different staging systems.
The Five Standard Stages
The most widely used framework assigns cancer a stage from 0 to 4 (often written with Roman numerals as 0 through IV). Here’s what each one means:
- Stage 0: Abnormal cells are found but haven’t invaded surrounding tissue. This is also called carcinoma in situ. It’s technically not cancer yet, but it can become cancer if left untreated.
- Stage 1: Cancer is present but small and only in the area where it started.
- Stage 2: The tumor is larger or has begun growing into nearby tissue, but hasn’t traveled far.
- Stage 3: Cancer has grown more extensively into surrounding tissue or reached nearby lymph nodes.
- Stage 4: Cancer has spread to distant organs or tissues. This is also called metastatic cancer.
Within each stage, letters like A, B, and C break things down further. A stage 3A breast cancer, for example, is less advanced than stage 3C. So while there are five broad stages, the substages create a much more detailed spectrum.
How Doctors Assign a Stage
The system behind those numbers is called TNM staging, maintained by the American Joint Committee on Cancer (AJCC). It evaluates three things: the size of the tumor and whether it has grown into nearby tissue (T), whether cancer has reached nearby lymph nodes (N), and whether it has metastasized to distant parts of the body (M). Each factor gets its own rating, and the combination determines the overall stage number.
For some cancers, staging now goes beyond tumor size and spread. Breast cancer staging, for instance, incorporates biological markers like hormone receptor status and genetic tests that predict how aggressively the cancer is likely to behave. A tumor that looks large on imaging might be assigned a lower stage if its biology suggests it will respond well to treatment. This shift means two people with similar-looking tumors can end up with different stage assignments based on the tumor’s molecular profile.
The AJCC periodically updates its staging guidelines. The current 8th edition covers most cancer types, while a newer 9th version is rolling out for specific cancers starting in 2026, beginning with salivary gland tumors and certain throat cancers.
Staging Before and After Surgery
You may hear your doctor refer to a clinical stage and a pathological stage. The clinical stage is the best estimate before surgery, based on imaging scans, biopsies, and physical exams. The pathological stage comes after surgery, when a pathologist examines the removed tumor and surrounding tissue under a microscope. The pathological stage is generally more accurate because the tissue is examined directly rather than estimated from the outside. The two don’t always match, so a stage assigned before surgery can shift afterward.
Cancers That Use Different Systems
Not every cancer follows the 0-to-4 framework. Blood cancers like leukemia don’t form solid tumors, so the TNM system doesn’t apply to them. Chronic lymphocytic leukemia, one of the most common leukemias in adults, uses two separate systems depending on where you live. In the United States, doctors typically use the Rai system, which has five stages (0 through IV) based on blood cell counts and whether the lymph nodes, spleen, or liver are enlarged. In Europe, the Binet system is more common. Some rarer blood cancers, like hairy cell leukemia, have no standard staging system at all.
Lymphomas use yet another approach called the Lugano classification, a modified version of the older Ann Arbor system. This focuses on how many groups of lymph nodes are involved and whether the cancer is on one or both sides of the diaphragm.
Brain and spinal cord tumors also follow their own rules. Instead of stages, they receive a grade from 1 to 4 assigned by the World Health Organization. These grades reflect how abnormal the cells look and how quickly the tumor is likely to grow, rather than how far it has spread. The WHO updated this system in 2021, incorporating molecular and genetic features alongside traditional microscopic appearance. To avoid confusion with staging used for other cancers, these are specifically labeled “CNS WHO grades.”
The Simplified Version for Survival Statistics
When you look up survival rates on sites like the National Cancer Institute, you’ll often see a simpler three-category system instead of stages 0 through 4. This system, used by the CDC and the SEER database, groups cancers as localized (confined to where it started), regional (spread to nearby lymph nodes or tissue), or distant (spread to other organs). These broader categories make it easier to compare outcomes across different cancer types, even though they sacrifice some detail. If you see a survival rate listed as “localized” or “distant,” this is the system being used.
Why Stage at Diagnosis Stays the Same
One thing that surprises many people: your cancer stage is typically set at diagnosis and doesn’t change, even if the cancer later progresses or responds to treatment. If a stage 2 cancer later spreads to the liver, it’s described as “stage 2 with distant metastasis” rather than being re-labeled stage 4. Doctors may restage for treatment planning purposes, but the original stage remains in your medical record because it serves as a baseline. This is why you might hear someone say they have “stage 2 metastatic” cancer, which can sound contradictory but reflects this convention.