Melanoma is staged from 0 to IV based on three factors: how deep the tumor has grown into the skin, whether it has reached nearby lymph nodes, and whether it has spread to distant organs. When caught at the earliest stages, the five-year survival rate is essentially 100%. At Stage IV, that number drops to 34%. Understanding what separates each stage helps you make sense of a diagnosis and what comes next.
How Melanoma Is Staged
Doctors use a system called TNM staging, which stands for Tumor, Nodes, and Metastasis. The “T” describes the primary tumor, specifically how deep it has grown (measured in millimeters) and whether the skin over it has broken down, a feature called ulceration. The “N” captures whether cancer cells have reached nearby lymph nodes. The “M” indicates whether cancer has spread to distant parts of the body.
Tumor depth is measured by a pathologist under a microscope after a biopsy. This measurement, called Breslow depth, runs from the top of the tumor (or the base of an ulcer, if the skin is broken) down to the deepest cancer cells. A fraction of a millimeter can shift the stage, which is why precise measurement matters so much. The current staging system is the AJCC 8th edition, which remains the standard as of 2025.
Stage 0: Melanoma in Situ
At Stage 0, abnormal melanocytes are confined entirely to the epidermis, the outermost layer of skin. The cancer has not invaded deeper tissue, has not reached lymph nodes, and has no potential to spread in its current state. Treatment is straightforward: surgical removal of the affected skin with a small margin of healthy tissue around it. Cure rates at this stage are extremely high.
Stage I: Thin, Localized Tumors
Stage I melanoma is still confined to the skin, with no evidence of spread to lymph nodes or distant sites. What separates it from Stage 0 is that the cancer has begun growing into deeper layers of skin.
Stage IA tumors are less than 0.8 mm thick without ulceration, or up to 1 mm thick without ulceration. Stage IB tumors are either less than 0.8 mm with ulceration or between 1 and 2 mm thick without ulceration. Treatment involves surgical excision. For Stage IB, doctors typically recommend a sentinel lymph node biopsy, a procedure where the first lymph node that drains the tumor site is removed and checked for cancer cells. For the thinnest, non-ulcerated tumors (Stage IA), this biopsy is generally not needed.
Stage II: Thicker Tumors, No Lymph Node Spread
Stage II melanoma is still localized to the skin, but the tumor is thicker, which increases the risk that cancer cells could eventually travel to lymph nodes or other organs. Ulceration plays a major role in distinguishing the substages.
- Stage IIA: The tumor is 1.1 to 2 mm thick with ulceration, or 2.1 to 4 mm thick without ulceration.
- Stage IIB: The tumor is 2.1 to 4 mm thick with ulceration, or more than 4 mm thick without ulceration.
- Stage IIC: The tumor is more than 4 mm thick with ulceration. This is the highest-risk substage before lymph node involvement is confirmed.
Treatment at Stage II involves wider surgical excision along with sentinel lymph node biopsy. Depending on the substage and risk factors, adjuvant therapy (treatment given after surgery to reduce the chance of recurrence) with immunotherapy may also be recommended. Stage IIC in particular carries a recurrence risk that often warrants this additional treatment.
Stage III: Spread to Nearby Lymph Nodes
Stage III means melanoma cells have moved beyond the primary tumor site and reached nearby lymph nodes or the skin between the tumor and the nearest lymph nodes. This stage is divided into four substages: IIIA, IIIB, IIIC, and IIID, based on the thickness and ulceration of the original tumor combined with the extent of lymph node involvement.
Lymph node involvement can be detected in two ways. Sometimes cancer cells are found only under a microscope during a sentinel lymph node biopsy, before any nodes are large enough to feel. Other times, affected lymph nodes are large enough to be detected on a physical exam or imaging scan. The distinction matters: cancer that is only detectable microscopically generally carries a better prognosis than nodes you can feel or see on a scan.
Stage III also accounts for satellite tumors (small clusters of cancer cells near the primary tumor), microsatellite tumors (tiny clusters found under the microscope), and in-transit metastases (cancer deposits in the skin or tissue between the original tumor and the nearest lymph nodes). Any of these findings, even without confirmed lymph node involvement, places melanoma in Stage III.
At the lower end, Stage IIIA involves a thin tumor (up to 2 mm without ulceration or up to 1 mm with ulceration) with cancer found in one to three lymph nodes only by biopsy. At the upper end, Stage IIID involves a thick, ulcerated tumor (over 4 mm) with cancer in four or more lymph nodes or nodes that are matted together. Treatment for resectable Stage III melanoma typically includes surgery followed by immunotherapy or, in some cases, immunotherapy given before surgery (neoadjuvant therapy) to shrink the tumor and improve surgical outcomes.
Stage IV: Distant Metastasis
Stage IV melanoma has spread beyond the regional lymph nodes to distant parts of the body. The most common sites include the lungs, liver, brain, bone, and distant skin or soft tissue. Where the cancer has spread determines the subcategory.
Distant skin, soft tissue, or distant lymph nodes represent the M1a category. Lung metastases fall under M1b. Spread to other organs (excluding the brain) is classified as M1c. Brain metastases, with or without disease in other locations, are designated M1d. Doctors also measure a blood marker called LDH (lactate dehydrogenase); elevated levels at any site of metastasis indicate a worse prognosis.
Treatment for Stage IV has changed dramatically in recent years. Immunotherapy, which helps the immune system recognize and attack cancer cells, is now a primary treatment. For patients whose tumors carry specific genetic mutations, targeted therapies that block the signals driving cancer growth are another option. In some cases, surgery to remove isolated metastases is also considered. While Stage IV carries a five-year survival rate of 34%, this number has been improving steadily as newer treatments become available.
Why Ulceration Matters So Much
You’ll notice ulceration appearing repeatedly across the staging criteria. An ulcerated melanoma, one where the overlying skin has broken down, behaves more aggressively than a non-ulcerated tumor of the same thickness. A 3 mm tumor without ulceration is Stage IIA, but the same 3 mm tumor with ulceration jumps to Stage IIB. This single feature can shift the entire treatment plan, potentially adding immunotherapy after surgery or changing follow-up schedules.
Survival by Stage
The National Cancer Institute’s SEER database groups survival data into three broad categories rather than individual stages. For melanoma confined to the primary site (which includes Stages 0 through II), the five-year relative survival rate is 100%. When cancer has spread to regional lymph nodes (Stage III), that rate drops to 76%. For distant metastatic disease (Stage IV), the five-year survival rate is 34%.
These numbers represent averages across large populations, and individual outcomes vary considerably based on the specific substage, the patient’s overall health, and the treatments used. The survival figures for Stage IV in particular are expected to continue improving as immunotherapy and targeted therapy become more refined and widely used.