Skin cancer is the most common cancer in the United States. A malignant melanoma is a cancerous neoplasm in which atypical melanocytes are present in both the epidermis and the dermis (and sometimes the subcutaneous cells). It is the most lethal of all skin cancers. Malignant melanoma can occur in one of several forms: superficial spreading melanoma, lentigo-maligna melanoma, nodular melanoma, and acral-lentiginous melanoma.
Most melanomas are derived from cutaneous epidermal melanocytes; some appear in pre-existing nevi (moles) in the skin or develop in the uveal tract of the eye. Melanomas occasionally appear simultaneously with cancer of other organs. The incidence and mortality rates of malignant melanoma are increasing, probably related to increased recreational sun exposure and better early detection. Prognosis is related to the depth of dermal invasion and the thickness of the lesion. Malignant melanoma can spread through both the bloodstream and the lymphatic system and can metastasize to the bones, liver, lungs, spleen, central nervous system (CNS), and lymph nodes.
Risk Factors
The cause of malignant melanoma is unknown, but ultraviolet rays are strongly suspected. Risk factors include the following:
- Fair-skinned or freckled, blue-eyed, light-haired
- Celtic or Scandinavian origin
- Tendency to burn and not tan; significant history of severe sunburn
- Environmental exposure to intense sunlight (older Americans retiring to the southwestern United States and countries near the equator)
- Family or personal history of melanoma, the absence of a gene on chromosome 9P, presence of giant congenital nevi
- Dysplastic nevus syndrome
Superficial Spreading Melanoma
- Most common form; usually affects middle-aged people, occurs most frequently on trunk and lower extremities
- Circular lesions with irregular outer portions
- Margins of lesion flat or elevated and palpable
- May appear in combination of colors, with hues of tan, brown, and black mixed with gray, blue-black, or white; sometimes a dull, pink-rose color noted in a small area within the lesion
Lentigo-Maligna Melanoma
- Slowly evolving pigmented lesion
- Occurs on exposed skin areas; hand, head, and neck in older adults
- First appears as tan, flat lesion, which in time undergoes changes in size and color
Nodular Melanoma
- Spherical, blueberrylike nodule with relatively smooth surface and uniform blue-black color
- May be dome-shaped with a smooth surface or have other shadings of red, gray, or purple
- May appear as irregularly shaped plaques
- May be described as a blood blister that fails to resolve
- Directly invades the adjacent dermis (vertical growth); poor prognosis
Acral-Lentiginous Melanoma
- Occurs in areas not excessively exposed to sunlight and where hair follicles are absent
- Found on the palms of the hands, soles, in nail beds, and mucous membranes in dark-skinned people
- Appears as an irregular pigmented macule that develops nodules
- Becomes invasive early
Outline
Treatment depends on the level of invasion and the depth of the lesion. In addition to surgery, chemotherapy and induced hyperthermia may be used to enhance treatment. Investigators are exploring the potential for the use of lipid-lowering medications and vaccine therapy to prevent melanoma.
Surgical Management
- Surgical excision is the treatment of choice for small superficial lesions.
- Deeper lesions require wide local excision and skin graft.
- A regional lymph node dissection may be performed to rule out metastasis, although newer approaches call for sentinel node biopsy to avoid problems from extensive lymph node removal.
- Debulking the tumor or other palliative procedures may be performed.