Stage 1 melanoma is the earliest stage of invasive melanoma, meaning cancer cells have grown into the skin but remain thin and localized. Tumors at this stage measure 1 millimeter or less in thickness and show no signs of spreading to lymph nodes or other parts of the body. The five-year relative survival rate for localized melanoma is 100%, making this one of the most treatable cancer diagnoses.
How Stage 1 Is Defined
Staging depends on two key measurements from your biopsy: how deep the tumor has grown into the skin (called Breslow thickness) and whether the surface skin over the tumor is broken (ulceration). A pathologist measures tumor depth from the top layer of skin down to the deepest cancer cells, or from the base of any ulcer if one is present.
Stage 1 breaks into two subcategories:
- Stage 1A: The tumor is less than 0.8 mm thick with no ulceration.
- Stage 1B: The tumor is less than 0.8 mm thick with ulceration, or 0.8 to 1.0 mm thick with or without ulceration.
In both cases, the melanoma has not reached any lymph nodes (N0) and has not spread to distant sites (M0). An older version of the staging system also factored in how quickly the tumor cells were dividing (mitotic rate), but the current system, adopted in 2018, removed that as a staging criterion. Mitotic rate is still recorded by pathologists because it helps guide treatment decisions, but it no longer changes your official stage.
What Treatment Looks Like
The primary treatment for stage 1 melanoma is surgery to remove the tumor along with a margin of healthy skin around it. If you’ve already had a biopsy that removed the visible mole, this second procedure, called a wide local excision, ensures no cancer cells remain at the edges. For tumors under 1 mm thick, the recommended surgical margin is 1 centimeter of normal skin on all sides. The procedure is typically done under local anesthesia in an outpatient setting, and most people go home the same day.
For stage 1B tumors, your doctor may also discuss a sentinel lymph node biopsy. This involves removing the one or two lymph nodes closest to the tumor site to check for microscopic cancer spread. The likelihood of finding cancer in these nodes for thin melanomas is roughly 5%, rising to about 8.8% for tumors 0.75 mm or thicker. Because the chance is relatively low, sentinel lymph node biopsy in stage 1B is considered optional and somewhat controversial. Factors like ulceration, a high mitotic rate, and signs of the tumor invading nearby lymph or blood vessels may tip the decision toward doing the biopsy.
Recurrence Risk Over Time
While the overall outlook is excellent, stage 1 melanoma does carry a small but real risk of coming back. Ten-year recurrence-free survival is approximately 88% to 91% for stage 1A and 79% to 80% for stage 1B, based on data from large patient registries published in the Journal of Clinical Oncology. That means roughly 9 to 12 out of 100 people with stage 1A, and 20 to 21 out of 100 with stage 1B, will experience some form of recurrence within a decade.
When recurrences do happen, about half are local, meaning the melanoma returns near the original site. Local recurrences can often be treated surgically. The rest may appear in nearby lymph nodes or, less commonly, in distant organs. This is why long-term monitoring matters even when the initial prognosis is favorable.
Follow-Up Schedule After Treatment
After your excision heals, you’ll enter a monitoring phase that lasts at least 10 years. The typical schedule depends on your specific substage. For stage 1 tumors under 1 mm, most guidelines recommend a skin and lymph node exam every six months for the first three to five years, then every six to twelve months through year 10. Your doctor will check the surgical scar, surrounding skin, and nearby lymph nodes at each visit.
Between appointments, you play an active role. Monthly self-exams of your skin and lymph nodes help catch any changes early. You’re looking for new or changing moles anywhere on your body, not just near the original site, as well as any lumps under the skin in your armpits, groin, or neck. People who’ve had one melanoma have a higher lifetime risk of developing a second, unrelated one, so these self-checks remain important indefinitely.
What Ulceration Means for Your Prognosis
Ulceration is the single feature that can shift a very thin melanoma from stage 1A to 1B. Under a microscope, ulceration means the layer of skin covering the tumor has broken down. You might notice this as a spot that bleeds or doesn’t heal, though sometimes ulceration is only visible on the biopsy slide.
Ulcerated melanomas tend to behave more aggressively than non-ulcerated ones of the same thickness. This is reflected in the roughly 10-percentage-point gap in 10-year recurrence-free survival between stage 1A and 1B. If your pathology report mentions ulceration, it doesn’t mean a bad outcome, but it does mean your care team will likely recommend closer monitoring and may be more inclined to offer a sentinel lymph node biopsy.
Understanding Your Pathology Report
After your biopsy or excision, you’ll receive a pathology report with several terms worth understanding. Breslow thickness is the most important number and directly determines your T category and stage. It’s reported in millimeters, often to the nearest tenth (for example, 0.6 mm or 0.9 mm).
Other details you may see include Clark level, which describes how deeply the tumor has penetrated into the structural layers of skin, and mitotic rate, reported as the number of dividing cells per square millimeter. While neither of these factors changes your official stage under current guidelines, both help your doctor assess your individual risk. A tumor that’s 0.7 mm thick but shows a high mitotic rate and ulceration warrants different follow-up than a 0.7 mm tumor without those features. Your report will also note whether the surgical margins are clear, meaning no cancer cells were found at the edges of the removed tissue. Clear margins are the goal and typically mean no further surgery is needed.