American Melanoma Institute · 4 min read
What melanoma stages 0 through IV mean under the AJCC 8th edition system, which tests set the stage, and how to read survival figures.
A stage is a short label for how far a melanoma has grown or spread at the time of diagnosis. Doctors use it to choose treatment, to decide which tests are worth doing, and to estimate the chance of the cancer returning. In the United States, staging follows the 8th edition of the American Joint Committee on Cancer (AJCC) manual.
T describes the tumor in the skin: its Breslow thickness in millimeters and whether the surface is ulcerated. N describes spread to nearby lymph nodes, and to the skin or lymph channels between the tumor and those nodes. M describes spread to distant parts of the body.
Doctors combine the 3 letters into a stage from 0 to IV. A lower-case a or b after the T number tells you whether ulceration is absent or present.
Stage 0 is melanoma in situ. The abnormal cells sit only in the epidermis, the top layer of skin, and haven't reached the vessels that could carry them elsewhere. Surgery to remove the area with a rim of normal skin is the usual treatment.
Stage I melanomas are thin and show no sign of spread. Under pathologic staging, stage IA covers tumors up to 1.0 mm thick, and stage IB covers tumors over 1.0 to 2.0 mm without ulceration. Treatment is wide excision, sometimes with a sentinel lymph node biopsy.
Stage II melanomas are thicker or ulcerated, still with no detected spread. Stage IIA includes tumors over 1.0 to 2.0 mm with ulceration and tumors over 2.0 to 4.0 mm without it. Stage IIB includes tumors over 2.0 to 4.0 mm with ulceration and tumors over 4.0 mm without it. Stage IIC is over 4.0 mm with ulceration.
Doctors usually recommend a sentinel lymph node biopsy along with wide excision for stage II. For stages IIB and IIC, they may also discuss adjuvant immunotherapy, meaning a checkpoint inhibitor such as pembrolizumab or nivolumab given after surgery to lower the chance of recurrence.
Stage III means the melanoma has reached nearby lymph nodes or the tissue on the way to them. That includes melanoma found in a sentinel node, lymph nodes a doctor can feel, and small deposits near the original tumor called microsatellites, satellites, or in-transit metastases.
The 8th edition splits stage III into 4 groups, IIIA through IIID, based on both the N findings and the thickness and ulceration of the original tumor. The groups differ widely in outlook. Treatment can include surgery, immunotherapy or targeted therapy after surgery, and in some cases immunotherapy before surgery.
Stage IV means melanoma has spread to distant sites. The M category records where: distant skin, soft tissue, or lymph nodes (M1a), lung (M1b), other internal organs (M1c), or the brain and spinal cord (M1d), a category new to the 8th edition. A blood level of lactate dehydrogenase (LDH) is recorded alongside.
Drug treatment is the main approach at this stage: immunotherapy for most patients, and targeted therapy when the tumor carries a BRAF gene change. Surgery and radiation treat individual sites when that helps.
Staging happens in steps. The clinical stage comes first, from the biopsy report and a physical exam of the skin and lymph nodes. The pathologic stage comes after surgery, when the wide excision specimen and any sentinel nodes have been examined.
The 2 can differ. A melanoma that looked like clinical stage II becomes stage III if the sentinel node contains melanoma cells. The labels also differ slightly at the thin end: a T1b melanoma counts as clinical stage IB, and as pathologic stage IA once the lymph nodes are shown to be clear.
Imaging such as CT, PET, or MRI of the brain is generally reserved for stage III and IV, for some stage IIB and IIC cases, and for anyone with symptoms that need explaining. For thin melanomas without symptoms, guidelines advise against routine scans, because they find harmless abnormalities far more often than hidden melanoma.
The AJCC 8th edition analysis (Gershenwald and colleagues, CA: A Cancer Journal for Clinicians, 2017) drew on more than 46,000 patients from 10 centers. It reported 5-year melanoma-specific survival of 98% for stage I, 90% for stage II, and 77% for stage III. Within stage III the range ran from 93% for IIIA to 32% for IIID.
Stage IIC, at 82%, had lower survival than stage IIIA. A thick, ulcerated tumor with clear nodes can carry more risk than a thin tumor with a few cells in one node, which is why doctors read the full T, N, and M detail behind the Roman numeral.
The American Cancer Society reports a different set of figures from the national SEER registry, which groups cases as localized, regional, or distant. For people diagnosed from 2015 to 2021, 5-year relative survival was over 99% for localized melanoma, 76% for regional, and 36% for distant.
Both sets of numbers describe large groups, and no individual. They can't account for a person's age, health, tumor genetics, or response to treatment. They also look backward. Many patients in the AJCC database were treated before modern immunotherapy and targeted therapy existed, and the AJCC panel chose not to publish new stage IV figures because treatment was changing so fast.
