Melanoma staging — what each stage means and what comes next

When melanoma is diagnosed, the next question is how far has it gone. Staging answers that — and it drives every treatment decision: surgical margins, whether to do a sentinel lymph node biopsy, whether imaging is needed, whether immunotherapy or targeted therapy is offered. This page explains what each stage means, what workup typically follows, and what treatment usually looks like.

When staging happens — and how long it takes

Stage usually isn't known the day you get your biopsy result. The biopsy confirms that it's melanoma; staging confirms how deep, whether nearby lymph nodes are involved, and whether it has spread anywhere else. That picture comes together over days to a few weeks after biopsy through:

• Pathology review of the biopsy specimen — Breslow thickness, ulceration, mitotic rate.
• A full physical and skin exam, including palpation of regional lymph nodes.
• For thicker melanomas, a sentinel lymph node biopsy (SLNB) — usually done at the same time as the wide local excision.
• For higher stages, imaging (CT, MRI, PET-CT) and a baseline LDH blood test.
• For Stage III and IV, molecular testing of the tumor — most importantly BRAF, sometimes NRAS or KIT — because these change which treatments are options.

The system used today is the AJCC 8th Edition, published in 2018. It uses TNM — Tumor (depth + ulceration), Node (involvement of lymph nodes), Metastasis (spread to distant sites) — to assign a stage from 0 to IV.

The vocabulary on your pathology report

These five terms drive everything that follows. Ask your team to explain yours, and ask for a written copy of the report.

Breslow thickness

How deep the melanoma reaches into the skin, measured in millimeters from the top layer down. Thinner is better. The thresholds that move you between substages are 0.8 mm, 1.0 mm, 2.0 mm, and 4.0 mm.

Ulceration

Whether the surface of the melanoma is broken open. Ulcerated melanomas behave more aggressively and bump up the substage at every level (e.g. a 1.5 mm tumor without ulceration is IIA; with ulceration it's IIB).

Mitotic rate

How many tumor cells per square millimeter are dividing. Higher rates mean faster-growing disease. AJCC 8 de-emphasized this in formal staging but most pathology reports still include it because clinicians find it useful.

Sentinel lymph node biopsy (SLNB) result

SLNB locates the first lymph node that drains from the melanoma site and tests it for melanoma cells. A positive SLNB moves the stage to III, even if no nodes were palpable on exam. SLNB is a procedure done under anesthesia; it's the single most important test for accurate staging in intermediate-thickness melanomas.

LDH (lactate dehydrogenase)

A blood test. Elevated LDH at Stage IV is a poor prognostic sign and bumps the M-substage from M1(0) to M1(1). Not used to stage earlier disease.

The five stages

Stage 0 — melanoma in situ

The melanoma is confined to the top layer of skin (the epidermis) and has not invaded deeper. By definition, it can't spread because it hasn't reached blood vessels or lymphatics. Highly curable.

Typical workup: Pathology confirms no invasion. Imaging is not standard. Sentinel lymph node biopsy is not done.

Typical treatment: Wide local excision (WLE) with a clinical margin of 0.5–1.0 cm around the lesion. For lentigo maligna (a subtype on chronically sun-damaged skin) the visible edge often understates the real edge — staged excision or wider margins may be used. Topical imiquimod or radiation are alternatives in selected cases. Cure rate with complete excision is essentially 100%.

Stage I — thin invasive, no spread

The melanoma has invaded past the epidermis into the dermis but is still relatively thin (≤2 mm Breslow), with no detected involvement of lymph nodes or distant sites.

Typical workup: Full skin exam plus palpation of regional lymph nodes. Routine imaging is not recommended for asymptomatic Stage I patients. SLNB is discussed for Stage IA (≤0.8 mm without ulceration) when other risk factors are present (high mitotic rate, lymphovascular invasion, young age), and offered for Stage IB (≥0.8 mm OR any ulceration).

Typical treatment: Wide local excision with 1 cm margins for tumors ≤1 mm (T1) and 1–2 cm margins for tumors 1.01–2 mm (T2). Adjuvant systemic therapy is not routine at Stage I.

Stage II — thicker localized melanoma

The melanoma is thicker (>2 mm, or >1 mm with ulceration) but still has not reached lymph nodes or distant sites. Higher Stage II (IIB and IIC in particular) carries meaningful recurrence risk despite being formally "localized."

Typical workup: Full skin exam and lymph node palpation. Sentinel lymph node biopsy is recommended. Baseline imaging (CT chest/abdomen/pelvis ± brain MRI) and an LDH blood draw are commonly obtained for Stage IIB and IIC. BRAF testing on the tumor may be done, especially if the team wants to keep targeted therapy as a future option.

Typical treatment: Wide local excision with margins by Breslow thickness — 1–2 cm for T2, 2 cm for T3 and T4 (>4 mm). Adjuvant immunotherapy with pembrolizumab or nivolumab is FDA-approved for high-risk Stage IIB and IIC after surgery, based on the KEYNOTE-716 (pembrolizumab) and CheckMate 76K (nivolumab) trials. Adjuvant therapy is a discussion, not automatic — it has real side effects and the absolute benefit depends on individual risk.

Stage III — regional lymph node involvement

Melanoma cells have reached at least one regional lymph node, or there are in-transit deposits or satellite metastases (small nodules of tumor between the primary site and the draining nodes). Distant sites are still clear. Stage III has four substages — IIIA, IIIB, IIIC, IIID — defined by the number of nodes, whether they're microscopic or clinically visible, ulceration of the primary, and primary tumor thickness. Prognosis varies enormously across these substages.

Typical workup: CT of chest, abdomen, and pelvis. Brain MRI for higher Stage III. LDH baseline. BRAF mutation testing on the tumor is essential because it determines eligibility for targeted therapy. NRAS, NF1, and broader sequencing in selected cases.

Typical treatment: Wide local excision of the primary plus management of the involved nodes — historically a completion lymph node dissection, more often today nodal observation with serial ultrasound surveillance (based on MSLT-II and DeCOG-SLT trials, which showed surveillance is non-inferior for survival in many cases). Adjuvant immunotherapy (pembrolizumab or nivolumab) is the standard for Stage III after surgery. For BRAF V600-mutant melanoma, adjuvant dabrafenib + trametinib (BRAF + MEK inhibitor combination) is an alternative. Treatment is for one year.

Stage IV — distant metastases

Melanoma has spread to distant sites. Substages reflect where: M1a (distant skin, soft tissue, or non-regional lymph nodes), M1b (lung), M1c (other internal organs — liver, bone), M1d (central nervous system / brain). LDH (normal or elevated) further modifies each substage.

Typical workup: Full-body imaging — usually PET-CT or contrast CT of chest, abdomen, pelvis, and neck. Brain MRI is essential because melanoma metastasizes to brain often and brain mets change urgency. LDH. Comprehensive molecular testing — BRAF, NRAS, KIT, sometimes NF1 and a broader panel — to guide systemic therapy choice.

Typical treatment: Systemic therapy is first-line. Categories:

• Combination immunotherapy. Nivolumab + ipilimumab (PD-1 + CTLA-4) — the longest-running combination, with the strongest long-term data but also the most side effects. Or nivolumab + relatlimab (PD-1 + LAG-3, branded as Opdualag) — approved 2022, generally better tolerated than nivo+ipi.
• Single-agent PD-1 immunotherapy. Pembrolizumab or nivolumab. Lower side-effect rate than the combinations; often the right starting point for older or frailer patients.
• Targeted therapy for BRAF V600-mutant melanoma. BRAF + MEK inhibitor combinations: dabrafenib + trametinib, encorafenib + binimetinib, vemurafenib + cobimetinib. Fast responses; durability is more limited than immunotherapy.
• TIL therapy. Lifileucel (Amtagvi), FDA-approved February 2024 for melanoma that has progressed on prior immunotherapy. A one-time infusion of a patient's own tumor-infiltrating lymphocytes after they've been expanded in a lab.
• Brain metastases: stereotactic radiosurgery (SRS) or whole-brain radiation in addition to systemic therapy, depending on number, size, and location.
• Surgery for isolated, accessible metastases (oligometastatic disease) in selected cases.

Prognostic gene-expression tests — when they may help

Two commercial tests look at gene activity in the biopsy specimen to refine prognosis or predict sentinel lymph node status. Neither is universally recommended — your team will say whether one applies to your situation. They're decision-support tools, not standalone treatment-deciders.

DecisionDx-Melanoma (Castle Biosciences)

A 31-gene expression profile that estimates 5-year metastasis risk in Stage I–III cutaneous melanoma. The result lands in one of four buckets: Class 1A (lowest risk), 1B, 2A, or 2B (highest risk).

Most useful when:

• The pathology is in a gray zone — for example, a thin Stage I tumor with one or two concerning features, where the team is weighing whether to recommend SLNB or skip it.
• Tailoring the frequency or intensity of surveillance imaging at Stage IIA–IIIA — a low-risk Class 1A may support less imaging; a Class 2B may support more.
• Borderline candidates for adjuvant therapy at high-risk Stage II — a high Class 2B result strengthens the case for adjuvant immunotherapy.

Less useful for: melanoma in situ (Stage 0 — no metastatic risk to predict), confirmed Stage IV (treatment is already escalated), or cases where the answer wouldn't change the plan.

Merlin Assay / CP-GEP (SkylineDx)

A separate gene-expression test that predicts the likelihood of a positive sentinel lymph node biopsy. Reports the patient as low risk or higher risk for nodal involvement.

Most useful when:

• You're a borderline candidate for SLNB — typically T1b or T2a — and your team wants to weigh whether the procedure is worth its risks (anesthesia, lymphedema, surgical complications) given a low predicted yield.
• A very low Merlin score may support safely deferring SLNB; a higher score reinforces doing it.

Caveats that apply to both

• Not yet standard-of-care. NCCN guidelines acknowledge GEP testing exists but do not require or universally endorse it. Use is most established in U.S. private-practice dermatology and select academic programs.
• Insurance coverage varies. Coverage depends on stage, payer, and whether the result will change management. Ask before assuming.
• One input among many. A GEP result doesn't override Breslow thickness, ulceration, SLNB, or imaging. It refines a probability, not a verdict.
• Ask: would the result change the plan? If you and your team agree on the next step regardless of what the test shows, the test isn't worth ordering.

Substages — the letters after the number

Within Stages I, II, and III, the letter (IA, IB, IIA, IIB, IIC, IIIA–IIID) is determined by combinations of Breslow thickness, ulceration, and lymph node detail. Stage IV uses M1a/b/c/d plus a "(0)" or "(1)" for normal vs elevated LDH.

The substages matter. Two people both at "Stage III" can have very different prognoses depending on whether they're IIIA (typically the best Stage III prognosis) or IIID (the worst). When you ask your team for "your stage," ask for the full stage including the letter — and the M-substage and LDH for Stage IV.

The full AJCC 8th edition criteria are summarized at the NCI Melanoma Treatment PDQ (clinician-oriented), the AAD melanoma overview, and the ACS staging page.

5-year relative survival, by stage group

From the U.S. SEER program (NCI), 2014–2020, by SEER's three-tier summary stage:

• Localized (essentially Stages 0–II): about 99%
• Regional (Stage III): about 71%
• Distant (Stage IV): about 35%

Beyond the era effect, these are population averages — they pool people with very different individual circumstances, treatment access, and biology. For any one person at higher stages today, your team's read on your specific situation — your tumor's biology, response to treatment, comorbidities, performance status — is far more useful than a population average.

What stage tells you and what it doesn't

Stage drives:

• Surgical margins of the wide local excision
• Whether sentinel lymph node biopsy is recommended, offered, or not done
• Whether and what imaging and blood work are part of the workup
• Whether adjuvant therapy is offered after surgery
• For Stage IV, which systemic therapies are first-line

Stage does not perfectly predict outcome. Two patients at the same substage can have very different paths. Newer therapies — particularly immunotherapy — have changed survival curves in ways older statistics don't fully capture. What's most useful is asking your team for your expected next steps in writing, not your prognosis as a percentage.

If you're newly diagnosed, the Just diagnosed page has a 10-step orientation including questions to ask your doctor.

Where to learn more

• NCI — Melanoma Treatment (PDQ®) — clinician-level summary, regularly updated.
• American Academy of Dermatology — Skin cancer overview — patient-facing.
• American Cancer Society — Melanoma stages — patient-facing.
• ASCO Cancer.Net — Melanoma stages — patient-facing overview.
• Melanoma Research Alliance — Staging — patient-facing.
• StatPearls — Cutaneous Melanoma (NCBI Bookshelf) — clinician textbook chapter, freely available.
• NCCN Clinical Practice Guidelines — Melanoma — the U.S. consensus treatment framework. Patient versions are free; clinician guidelines require free registration.