Cancer is staged using a combination of imaging scans, biopsies, and sometimes surgery to determine how large a tumor is and how far it has spread. Most solid cancers are staged with the TNM system, which evaluates three things: the size of the primary tumor (T), whether cancer has reached nearby lymph nodes (N), and whether it has spread to distant parts of the body (M). These three factors are combined into an overall stage from 0 to IV, with higher numbers indicating more advanced disease.
The TNM System
The TNM system is the most widely used framework for staging cancer. Each letter represents a category that gets assigned a number based on test results. The T category describes the primary tumor’s size and how deeply it has grown into surrounding tissue. A T1 tumor is small and contained, while a T4 tumor has grown extensively into nearby structures. The N category describes whether cancer cells have reached regional lymph nodes, the small immune-system hubs near the tumor. N0 means no lymph node involvement; higher numbers mean more nodes are affected. The M category is the most straightforward: M0 means no distant spread, and M1 means cancer has been found in organs or tissues far from the original site.
These three values are then combined into an overall stage grouping, which is what most people hear from their doctor.
What Each Stage Means
Stage 0 describes abnormal cells that haven’t spread and aren’t considered cancer yet, though they could become cancerous. This is sometimes called “in situ,” meaning the cells are still confined to the tissue layer where they started.
Stages I through III describe cancers that haven’t spread beyond the primary tumor site or have only reached nearby tissue. The higher the number, the larger the tumor and the more it has spread into surrounding areas. A stage I cancer is typically small and localized. Stage II and III cancers are progressively larger, may have grown into adjacent structures, or may involve nearby lymph nodes.
Stage IV means the cancer has spread to distant areas of the body. This is also called metastatic cancer. Common sites of distant spread include the liver, lungs, bones, and brain, though the specifics depend on the type of cancer.
Tests Used to Determine Stage
Staging typically requires several types of tests, starting with imaging. CT scans take x-ray images from multiple angles and build a detailed 3D picture of your organs. MRI uses magnetic fields and radio waves to create high-resolution images, which are especially useful for soft tissue. PET scans work differently: you receive an injection of a glucose-based tracer, and the scan highlights areas where cells are consuming more sugar than normal, since cancer cells tend to be hungrier than healthy ones. Bone scans use a small amount of radioactive material to check whether cancer has reached the skeleton. Ultrasound and standard x-rays round out the toolkit for specific situations.
Imaging alone can’t confirm cancer. A biopsy, where a doctor removes a small sample of tissue for examination under a microscope, is needed in most cases. Biopsies can be done with a needle (common for breast, prostate, and liver cancers), through an endoscope (a thin lighted tube inserted through the mouth or rectum), or during surgery. The tissue sample reveals not only whether cancer is present but also how abnormal the cells look, which is called the tumor grade. Grade is separate from stage: it describes how aggressive the cells appear rather than how far the cancer has spread. Both pieces of information help guide treatment decisions.
PET-CT scans, which combine a PET scan with a CT scan, are commonly used to check whether cancer has spread to lymph nodes. A systematic review of studies involving nearly 1,500 patients found that PET-CT was very good at correctly identifying cancer-free lymph nodes (about 92% specificity) but less reliable at detecting nodes that did contain cancer (about 52% sensitivity). This is one reason staging sometimes requires a surgical biopsy of lymph nodes rather than relying on imaging alone.
Clinical Staging vs. Pathological Staging
You may hear your doctor refer to two different types of staging. Clinical staging is determined before surgery, based on physical exams, imaging, and biopsies. It gives doctors a working estimate of how advanced the cancer is and helps guide initial treatment planning. In medical records, this is sometimes written with a lowercase “c” before the TNM values (cT2N1M0, for example).
Pathological staging happens after surgery, when a pathologist can examine the removed tumor and surrounding tissue under a microscope. This combines the clinical findings with direct observation of the tumor and is generally considered more accurate. It’s written with a “p” prefix (pTNM). Not every patient undergoes surgery, so not every patient receives a pathological stage.
Cancers That Use Different Systems
The TNM system works well for most solid tumors, but some cancers require different approaches. Lymphomas, both Hodgkin and non-Hodgkin, are staged using the Ann Arbor system. Because lymphoma involves the lymphatic system rather than a single solid tumor, the TNM categories don’t apply. Ann Arbor staging uses stages I through IV based on how many lymph node regions are involved and whether the disease has spread to organs outside the lymphatic system.
Gynecological cancers, including ovarian, cervical, and vulvar cancers, often use the FIGO system developed by the International Federation of Gynecology and Obstetrics. FIGO uses Roman numerals and subscripts (like IIIA1 or IVB) to define stages but doesn’t break them into separate T, N, and M categories. A FIGO stage must come from the treating physician’s assessment and can’t simply be inferred from pathology reports alone.
How Staging Guides Treatment
The stage of your cancer is one of the biggest factors in determining what treatment you’ll receive. Early-stage cancers (stage I) are typically localized, meaning they’re confined to one area. Treatment usually focuses on removing or destroying the cancer at that site through surgery, radiation, or ablation therapy.
More advanced cancers often require systemic treatments, therapies that travel through your bloodstream to reach cancer cells throughout the body. These include chemotherapy, immunotherapy, hormone therapy, and targeted therapy, which are given as pills, injections, or IV infusions on a set schedule. Systemic treatments can destroy cancer cells that are too spread out to surgically remove or catch stray cells that local treatments might miss.
Stage III cancers often need a combination of both approaches. Surgery may still be the primary treatment, but you might receive radiation beforehand to shrink the tumor, followed by systemic therapy afterward to reduce the risk of recurrence. Stage IV cancers are more commonly treated with systemic therapy as the main strategy, though surgery and radiation may still play a role in specific situations.
Staging Standards Continue to Evolve
The staging system is maintained by the American Joint Committee on Cancer (AJCC), which periodically updates its criteria as medical knowledge advances. The AJCC recently shifted from publishing a single staging manual (the 8th edition is still in wide use) to releasing rolling updates by cancer type under a new “Version 9” system. Lung, thymus, and nasopharyngeal cancers transitioned to Version 9 criteria in 2025, with salivary gland and HPV-associated throat cancers following in 2026. Other cancer types will continue using 8th edition criteria until their Version 9 updates are released.
One area of active development is the liquid biopsy, a blood test that detects fragments of tumor DNA circulating in the bloodstream. At diagnosis, this type of test can help stratify risk in early-stage cancers and identify patients who might benefit from treatment before surgery. Liquid biopsies are currently being studied in clinical trials for both early-stage and advanced cancers to determine how they can best complement traditional staging methods.