Melanoma is a serious form of skin cancer, and understanding how it develops is an important step toward protecting your skin and improving awareness. Using information commonly shared by leading skin cancer centers, this guide explains how melanoma typically begins, what visible changes may signal a problem, and how clinicians classify melanoma into formal stages.
By learning what to look for—especially changes in moles or the appearance of a new, unusual spot—you can be better prepared to seek prompt evaluation and support early detection when it matters most.What Is Melanoma and How Does It Begin?
Melanoma is the most serious type of skin cancer. It develops in melanocytes, the cells that produce melanin (the pigment responsible for skin color). While it’s less common than other skin cancers such as basal cell carcinoma, melanoma is more dangerous because it can spread to other parts of the body if not treated early.
Often, the first sign is a noticeable change in an existing mole or the development of a new spot that looks unusual. Understanding typical progression helps you recognize these warning signs early. Dermatologists and organizations such as The Skin Cancer Foundation and the American Academy of Dermatology offer simple guidelines to help people identify concerning changes.
The ABCDEs: A Practical First Check
The most widely used method for spotting a suspicious mole is the ABCDE rule. This easy acronym highlights common melanoma warning signs.
- A is for Asymmetry: Picture a line drawn through the center of the mole. If the two halves don’t match, the mole is asymmetrical. Benign (noncancerous) moles are usually symmetrical.
- B is for Border: Early melanomas often have uneven borders. Edges may be scalloped, notched, or poorly defined, while benign moles typically have smooth, even borders.
- C is for Color: A mole showing more than one color can be a red flag. Look for different shades of brown, tan, or black; as melanoma progresses, red, white, or blue may also appear. Harmless moles are usually one uniform shade of brown.
- D is for Diameter: Melanomas are often larger than a pencil eraser (about 6 millimeters or ¼ inch), though they can be smaller when first detected.
- E is for Evolving: Any change in size, shape, color, elevation, or another trait—such as itching, bleeding, or crusting—can signal danger. If one mole looks different from the others on your body (the “Ugly Duckling” sign), it should be checked by a doctor.
The Formal Stages of Melanoma Progression
After melanoma is diagnosed, a dermatologist assigns a stage. Staging describes how deeply the cancer has grown and whether it has spread, helping guide treatment decisions and predict outcomes. The AJCC (American Joint Committee on Cancer) staging system ranges from Stage 0 through Stage IV.
Stage 0: Melanoma In Situ
Stage 0 is the earliest stage. “In situ” means “in its original place.” Cancer cells are confined to the epidermis (the outermost layer of skin) and have not invaded deeper layers. This stage is non-invasive and is almost always curable with simple surgical removal.
Stage I
In Stage I, melanoma is invasive, meaning it has grown below the epidermis into the dermis. Stage I is divided based on tumor thickness (Breslow depth) and whether ulceration is present (broken skin on the surface).
- Stage IA: The tumor is less than 1 millimeter thick and not ulcerated.
- Stage IB: The tumor is less than 1 millimeter thick and ulcerated, OR it is between 1 and 2 millimeters thick and not ulcerated.
Stage I melanoma generally has a very good prognosis, especially when treated early.
Stage II
Stage II melanomas are thicker than Stage I tumors but have not spread to nearby lymph nodes or distant parts of the body. Because of the increased thickness, the risk of spread is higher than in Stage I. Subcategories are based on thickness and ulceration.
- Stage IIA: The tumor is between 1 and 2 millimeters thick and ulcerated, OR it is between 2 and 4 millimeters thick and not ulcerated.
- Stage IIB: The tumor is between 2 and 4 millimeters thick and ulcerated, OR it is thicker than 4 millimeters and not ulcerated.
- Stage IIC: The tumor is thicker than 4 millimeters and ulcerated.
Stage III
Stage III melanoma means the cancer has spread beyond the original tumor to regional lymph nodes or nearby skin. This is considered advanced disease. While sub-staging can be complex, the key point is that the melanoma is no longer confined to the original skin site. Treatment is usually more involved and may include surgery to remove affected lymph nodes, along with immunotherapy or targeted therapy.
Stage IV
Stage IV is the most advanced stage, in which melanoma has metastasized (spread through the bloodstream) to distant organs and tissues. Common metastatic sites include the lungs, liver, brain, bones, and the gastrointestinal tract. Although Stage IV melanoma is very serious, newer treatments such as immunotherapy and targeted therapies have improved outcomes for many patients in recent years.
Frequently Asked Questions
How quickly does melanoma progress?
Progression speed varies widely depending on melanoma type and individual factors. Some forms, such as nodular melanoma, can grow and advance quickly—sometimes over weeks or months. Others, like lentigo maligna, may develop slowly over many years. Any new or changing spot should be evaluated promptly.
Can a normal mole turn into melanoma?
Yes. While many melanomas appear as new spots, roughly 20–30% develop from existing moles. This is why monitoring your current moles for ABCDE changes is just as important as watching for new ones.
What should I do if I find a suspicious spot?
Schedule an appointment with a board-certified dermatologist as soon as possible. Don’t wait to see whether it changes further. Early detection is the most important factor for successful treatment, and a dermatologist can perform a biopsy to determine whether a spot is cancerous.
Is melanoma always dark or brown?
No. Most melanomas are pigmented, but amelanotic melanoma is a rare type that lacks pigment. It can appear pink, reddish, white, or skin-colored and may resemble a pimple or a benign scar, making it harder to recognize.