The four stages of skin cancer describe how far the cancer has grown, from a small tumor confined to the skin (Stage 1) to cancer that has spread to distant organs like the lungs or brain (Stage 4). Most staging discussions focus on melanoma, the most dangerous form, but squamous cell carcinoma and basal cell carcinoma follow similar frameworks. There’s also a Stage 0, sometimes called “in situ,” where abnormal cells haven’t yet invaded deeper tissue. Understanding which stage you’re dealing with shapes every treatment decision that follows.
How Skin Cancer Staging Works
Doctors stage skin cancer using a system built around three factors: how thick or deep the original tumor is, whether cancer has reached nearby lymph nodes, and whether it has spread to distant parts of the body. For melanoma, the single most important measurement is tumor thickness, measured in millimeters from the surface of the skin down to the deepest point of invasion. This measurement, called Breslow depth, is what separates early stages from more advanced ones.
Ulceration also matters. A tumor is ulcerated when the skin covering it has broken down. Two melanomas of the same thickness will be staged differently if one is ulcerated and the other isn’t, because ulceration signals more aggressive behavior. The current staging system used in the United States is the eighth edition of the American Joint Committee on Cancer (AJCC) manual, which remains the standard for cutaneous cancers.
Stage 0: Melanoma in Situ
At Stage 0, abnormal melanoma cells exist only in the outermost layer of skin (the epidermis) and haven’t pushed into deeper tissue. This is sometimes called “in situ,” Latin for “in place.” It’s the most treatable point, with a five-year survival rate of essentially 100%. Treatment typically involves surgically removing the affected area with a margin of healthy skin around it. No lymph node evaluation is needed.
Stage 1: Thin, Localized Tumors
Stage 1 melanoma is still confined to the skin with no evidence of spread to lymph nodes or other organs. It’s divided into two substages based on thickness and ulceration.
Stage 1A tumors are 1 millimeter thick or less, with no ulceration. Stage 1B tumors are either less than 0.8 mm with ulceration, 0.8 to 1.0 mm with or without ulceration, or 1.1 to 2.0 mm without ulceration. These distinctions matter because they determine whether your doctor will recommend checking the nearest lymph node. For tumors thicker than 1.0 mm, guidelines recommend a sentinel lymph node biopsy, a procedure where the first lymph node that drains the tumor site is removed and examined for cancer cells. For thinner tumors (0.8 to 1.0 mm), this biopsy is considered on a case-by-case basis, especially in patients under 40 or when other risk factors are present.
The five-year survival rate for localized melanoma (Stages 1 and 2 combined) is 97.6%.
Stage 2: Thicker Tumors, Still Localized
Stage 2 melanoma is thicker than Stage 1 but still hasn’t spread beyond the original site. The cancer is entirely in the skin, with no lymph node involvement. What escalates the staging is greater depth and the presence of ulceration.
Stage 2A includes tumors 1.1 to 2.0 mm thick with ulceration, or 2.1 to 4.0 mm without ulceration. Stage 2B covers tumors 2.1 to 4.0 mm with ulceration, or tumors thicker than 4.0 mm without ulceration. Stage 2C, the highest substage, applies to tumors thicker than 4.0 mm that are also ulcerated.
Even though Stage 2 melanoma hasn’t visibly spread, thicker tumors carry a higher risk of microscopic spread that imaging can’t detect yet. A sentinel lymph node biopsy is routinely recommended for all Stage 2 tumors, since the probability of finding cancer cells in a nearby lymph node exceeds 10% once thickness passes 1.0 mm.
Stage 3: Spread to Nearby Lymph Nodes
Stage 3 marks the point where melanoma has moved beyond the original tumor site but hasn’t traveled to distant organs. Cancer cells have reached one or more regional lymph nodes, or they’ve appeared in the skin between the original tumor and the nearest lymph node cluster (called in-transit metastases or satellite lesions).
The primary tumor can be any thickness at this stage. What defines Stage 3 is evidence that at least one lymph node contains cancer cells. Sometimes this is detected during a sentinel node biopsy before a patient has any symptoms. Other times, a swollen or firm lymph node is physically noticeable. The number of involved lymph nodes and whether the cancer was detected microscopically or by physical exam both influence substaging and treatment planning.
The five-year survival rate drops significantly at this stage, to about 60.3%. Treatment often involves surgery to remove affected lymph nodes, frequently followed by immunotherapy or targeted therapy to reduce the chance of recurrence.
Stage 4: Distant Metastasis
Stage 4 melanoma means cancer has spread to distant parts of the body. The most common sites, in order, are skin and soft tissue far from the original tumor, lungs, liver, bones, and brain. The primary tumor can be any size, and any number of lymph nodes may or may not be involved.
Stage 4 is further subdivided based on where the cancer has traveled. Spread limited to distant skin, muscle, or far-away lymph nodes is classified differently from lung metastases, which in turn is classified separately from spread to organs like the liver. Brain involvement carries its own designation. At each of these levels, a blood marker called LDH (lactate dehydrogenase) plays a role: elevated LDH generally signals a worse prognosis within Stage 4.
The five-year survival rate for distant melanoma is 16.2%, though this number has been improving in recent years with advances in immunotherapy and targeted treatments. Some patients with Stage 4 disease now achieve long-term remission, something that was rare a decade ago.
Staging for Non-Melanoma Skin Cancers
Basal cell carcinoma and squamous cell carcinoma, the two most common skin cancers, are staged less frequently because they rarely spread. Basal cell carcinoma metastasis is extremely rare, so most cases are treated based on tumor characteristics rather than a formal stage assignment. When staging is applied, tumors under 2 cm with few aggressive features are classified as Stage 1, while larger tumors or those invading bone receive higher designations.
Squamous cell carcinoma uses a similar framework. Under the AJCC system, Stage 1 tumors are less than 2 cm across, Stage 2 tumors are 2 to 3.9 cm, and Stage 3 includes tumors 4 cm or larger, those invading beyond the fat layer beneath the skin, or those growing along nerves. Stage 4 involves invasion into major bone or the skull. A separate system developed at Brigham and Women’s Hospital stages squamous cell carcinoma based on the number of high-risk features present, including tumor size of at least 2 cm, poor differentiation under the microscope, nerve involvement, and deep tissue invasion.
For both basal cell and squamous cell carcinomas, the vast majority of cases are caught early and cured with surgery alone. Formal staging becomes important mainly for the small percentage of tumors that are large, aggressive, or recurrent.
What Determines Your Stage
After a suspicious mole or lesion is biopsied and confirmed as skin cancer, the pathology report provides the key details: how thick the tumor is, whether it’s ulcerated, and how deep it extends. For melanoma thicker than 0.8 mm, a sentinel lymph node biopsy is typically the next step to check for microscopic spread. Imaging scans (CT, PET, or MRI) are used when there’s concern about distant metastasis, particularly for thicker tumors or when lymph nodes test positive.
Staging isn’t always a one-time event. If melanoma recurs or new symptoms develop, restaging may be done to guide the next round of treatment. The overall five-year survival rate across all stages of melanoma is 90.5%, largely because most cases are caught at Stage 1 or 2, when the cancer is still localized and highly curable.