American Melanoma Institute · 5 min read
What stage 0 melanoma means, why the outlook is excellent, how surgeons choose margins, and what options exist when surgery is difficult.
Hearing the word melanoma is frightening, even with the words in situ attached. Stage 0 is the earliest point at which melanoma can be found, and treatment at this stage is expected to cure it.
Skin has 2 main layers. The epidermis on top is thinner than a sheet of paper and has no blood vessels or lymph vessels. The dermis beneath it contains both.
In situ is Latin for in place. In melanoma in situ, the cancerous pigment cells (melanocytes) are confined to the epidermis. They have not crossed the thin membrane that separates epidermis from dermis. Cancer cells need access to blood or lymph channels to travel, and cells that stay in the epidermis have none. This is why melanoma in situ, fully removed, does not spread.
The pathology report for an in situ melanoma lists no Breslow depth, since there is no invasion to measure. Sentinel lymph node biopsy, scans, and blood tests are not part of the workup.
DermNet, a dermatology reference written by physicians, states that people with melanoma in situ have the same life expectancy as the general population.
Treatment is still necessary. Left in place, some in situ melanomas eventually grow down into the dermis and become invasive, and at that point the tumor's thickness begins to affect prognosis.
Melanoma in situ comes in several patterns. Lentigo maligna is the type that needs the most explanation.
Lentigo maligna grows on skin with decades of sun damage, usually the cheek, nose, forehead, ear, or scalp, and most often in people between 60 and 80. It looks like a large, flat, irregular freckle with shades of tan, brown, and sometimes black or pink. It expands slowly. DermNet describes growth over 5 to 20 years or longer, and many are several centimeters wide by the time of diagnosis.
If it invades the dermis, the name changes to lentigo maligna melanoma. DermNet estimates that fewer than 5% of lentigo malignas progress this way, with a higher chance in very large patches. A new bump, thickening, a dark blue or black area, or bleeding within the patch raises suspicion of invasion.
Lentigo maligna has 2 features that complicate treatment. The abnormal melanocytes often extend well past the visible brown edge. And in chronically sun-damaged skin, even the normal melanocytes are more numerous and look somewhat irregular, so the pathologist has a harder time deciding where the melanoma ends.
Standard treatment for melanoma in situ is wide excision: removal of the biopsy site with a rim of normal-looking skin, down to the fat. The usual margin is 5 to 10 mm (0.5 to 1 cm).
A pathologist checks the edges of the removed tissue. If melanoma cells reach an edge, the American Cancer Society notes that a second, wider excision may be needed.
For lentigo maligna, a 5 mm margin often falls short because of the hidden extension described above. Guidelines from the American Academy of Dermatology acknowledge that margins wider than 5 mm may be necessary for this subtype. Surgeons developed margin-controlled techniques to solve this problem on the face.
These techniques share one idea: check 100% of the edge under the microscope before the wound is repaired, and remove more tissue only where melanoma remains.
In Mohs surgery, the surgeon removes the visible tumor with a narrow margin, maps it, and examines frozen sections of the entire edge the same day. Melanocytes are difficult to see on frozen tissue, so Mohs surgeons who treat melanoma use immunostains. These are antibody stains, most commonly MART-1 (also called Melan-A), that color melanocytes so they stand out. If any edge is positive, the surgeon takes more tissue from that exact spot and repeats the process.
Staged excision, sometimes called slow Mohs, works the same way, except that the tissue is sent to a pathology lab for permanent sections, often read by a dermatopathologist. The wound is bandaged between stages and repaired once all margins are clear.
The American Academy of Dermatology guideline describes both methods as providing exhaustive margin assessment while sparing tissue. The American Cancer Society is more reserved, noting that Mohs surgery is not standard for melanoma and that doctors disagree about its use.
Some patients are too frail for surgery, or have a patch so large that removal would be disfiguring. Doctors use 2 non-surgical treatments for lentigo maligna in these situations.
Imiquimod is a cream that provokes a local immune attack. A course lasts weeks to months and produces marked redness, crusting, and soreness. Its use for lentigo maligna is off-label, meaning the FDA has not approved it for this purpose. Radiation therapy, delivered to the skin surface over several sessions, is the other option.
The American Academy of Dermatology guideline advises that these approaches be considered only when surgery is impractical, because their cure rates are lower. Neither one yields a specimen that proves the margins are clear, so close follow-up is part of the plan. For a very elderly patient, careful observation with photographs is also an accepted choice.
Recurrence at the scar is uncommon after a complete excision. Lentigo maligna is the exception, with recurrence rates that DermNet puts as high as 20%.
The larger concern is a new, separate melanoma. People who have had melanoma in situ have about 8 times the usual risk of developing another melanoma, in situ or invasive, according to DermNet. Doctors generally recommend a full skin exam at least once a year for life, along with monthly self-exams.
