Melanoma

Melanoma
Melanoma
Specialty	Oncology

Melanoma is a malignant tumor of melanocytes and, less frequently, of retinal pigment epithelial cells (of the eye, see uveal melanoma). While it represents one of the rarer forms of skin cancer, melanoma underlies the majority of skin cancer-related deaths. Despite many years of intensive laboratory and clinical research, the sole effective cure is surgical resection of the primary tumor before it achieves a thickness of greater than 1 mm. Metastatic forms of the disease, where cells from the primary have moved to other parts of the body and proliferated, are extremely dangerous and patient survival rarely exceeds two years.

Causes

Epidemiologic studies from Australia suggest that exposure to ultraviolet radiation is one of the major contributors to the development of melanoma. This radiation causes errors in the Deoxyribonucleic Acid (DNA) of cells, making them go through Mitosis (cell division) at an unhealthy rate. Occasional extreme sun exposure (resulting in "sunburn") is causally related to melanoma. Those with more chronic long term exposure (outdoor workers) may develop protective mechanisms. Melanoma is most common on the back in men and on legs in women (areas of intermittent sun exposure) and is more common in indoor workers than outdoor workers (in a British study). Other factors are mutations in or total loss of tumor suppressor genes. Use of sunbeds (with deeply penetrating UVA rays) has been linked to the development of skin cancers, including melanoma.

Possible significant elements in determining risk include the intensity and duration of sun exposure, the age at which sun exposure occurs, and the degree of skin pigmentation. Exposure during childhood is a more important risk factor than exposure in adulthood. This is seen in migration studies in Australia where people tend to retain the risk profile of their country of birth if they migrate to Australia as an adult. Individuals with blistering or peeling sunburns (especially in the first twenty years of life) have a significantly greater risk for melanoma.

Fair and red-headed people are at greater risk for developing melanoma. A person with multiple atypical nevi or dysplastic nevi are at a significant risk. Persons born with giant congenital naevi are at increased risk.

A family history of melanoma greatly increases a person's risk. Certain 'melanoma families' display features of mendelian inheritance of cancer causing genes. It is critical that individuals with family members who have been diagnosed with melanoma be checked regularly for skin cancer. Patients with a history of one melanoma are at increased risk of developing a second primary tumour.

Prevention

Primary

Minimize exposure to sources of ultraviolet radiation (the sun and sunbeds)
Follow sun protection measures. Wearing protective clothing (long-sleeved shirts, long trousers, and broad-brimmed hats.) offers the best protection. Use a sunscreen with an SPF rating of 30 or better on exposed areas.

Secondary

A melanoma showing irregular borders and colour, diameter over 10mm and asymmetry (ie A, B, C and D.)

To prevent or detect melanomas (and increase survival rates), it is recommended that the public:

Learn what they look like (see "ABCDE" mnemonic below.)
Are aware of moles and check for changes (shape, size, color, itching or bleeding)
Show any suspicious moles to a doctor with an interest and skills in skin malignancy.

A popular method for remembering the signs and symptoms of melanoma is the mnemonic "ABCDE":

Asymmetrical skin lesion.
Border of the lesion is irregular.
Color: melanomas usually have multiple colors.
Diameter: moles greater than 5 mm are more likely to be melanomas than smaller moles.
Evolution: The evolution (ie change) of a mole or lesion may be a hint that the lesion is becoming malignant --or-- Elevation: The mole is raised or elevated above the skin.

People with a personal or family history of skin cancer or of dysplastic nevus syndrome (multiple atypical moles) should see a dermatologist at least once a year to be sure you are not developing melanoma.

Diagnosis

Any mole that is irregular in color or shape should be examined by a doctor to determine if it is a malignant melanoma, the most serious and life-threatening form of skin cancer. Following a visual examination and a dermatoscopic exam (an instrument that illuminates a mole, revealing its underlying pigment and vascular network structure), the doctor may biopsy the suspicious mole. If it is malignant, the mole and an area around it needs excision. This may require a referral to a surgeon or dermatologist.

The diagnosis of melanoma requires experience, as early stages may look identical to harmless moles or not have any color at all. Where any doubt exists, the patient will be referred to a specialist dermatologist. Beyond this expert knowledge a biopsy performed under local anesthesia is often required to assist in making or confirming the diagnosis and in defining the severity of the melanoma.

One method is a punch biopsy, using a surgical punch (an instrument similar to a tiny cookie cutter with a handle, with an opening ranging in size from 1 to 6 mm). The punch is used to remove a plug of skin (down to the subcutaneous layer) from a portion of a large suspicious lesion, or to completely remove a smaller lesion. Preferably, an excisional biopsy can be performed, where the suspect lesion is totally removed by cutting an ellipse of tissue around it. Both methods will include the epidermal, dermal, and subcutaneous layers of the skin in the biopsy specimen, enabling the pathologist to determine the depth of penetration of the melanoma by microscopic examination. This is described by Clark's level (involvement of skin structures) and Breslow's depth (measured in millimeters).

Lactate dehydrogenase (LDH) tests are often used to screen for metastases, although many patients with metastases (even end-stage) have a normal LDH; extraordinarily high LDH often indicates metastatic spread of the disease to the liver. It is common for patients diagnosed with melanoma to have chest X-rays and an LDH test, and in some cases CT, MRI, PET and/or PET/CT scans. Although controversial, sentinel lymph node biopsies and examination of the lymph nodes are also performed in patients to assess spread to the lymph nodes.

Sometimes the skin lesion may bleed, itch, or ulcerate, although this is a very late sign. A slow-healing lesion should be watched closely, as that may be a sign of melanoma. Be aware also that in circumstances that are still poorly understood, melanomas may "regress" or spontaneously become smaller or invisible - however the malignancy is still present. Amelanotic (colorless or flesh-colored) melanomas do not have pigment and may not even be visible. Lentigo maligna, a superficial melanoma confined to the topmost layers of the skin (found primarily in older patients) is often described as a "stain" on the skin. Some patients with metastatic melanoma do not have an obvious detectable primary tumor.

Types of Primary Melanoma

In the skin:

Any of the above types may produce melanin (and be dark in colour) or not (and be amelanotic - not dark). Similarly any subtype may show desmoplasia (dense fibrous reaction with neurotropism) which is a marker of aggressive behaviour and a tendency to local recurrence.

Elsewhere:

Prognostic factors

Features that affect prognosis are tumor thickness in millimeters (Breslow's depth), depth related to skin structures (Clark level), type of melanoma, presence of ulceration, presence of lymphatic/perineural invasion, presence of tumor infiltrating lymphocytes (if present, prognosis is better), location of lesion, presence of satellite lesions, and presence of regional or distant metastasis.

Certain types of melanoma have worse prognoses but this is explained by their Breslow's depth. Interestingly, less invasive melanomas even with lymph node metastases carry a better prognosis than deep melanomas without regional metastasis at time of staging. Local recurrences tend to behave similarly to a primary unless they are at the site of a wide local excision (as opposed to a staged excision or punch/shave excision) since these recurrences tend to indicate lymphatic invasion.

When melanomas have spread to the lymph nodes, one of the most important factors is the number of nodes with malignancy. Extent of malignancy within a node is also important; micrometastases in which malignancy is only microscopic have a more favorable prognosis than macrometastases. In some cases micrometastases may only be detected by special staining, and if malignancy is only detectable by a rarely-employed test known as polymerase chain reaction (PCR), the prognosis is better. Macrometastases in which malignancy is clinically apparent (in some cases cancer completely replaces a node) have a far worse prognosis, and if nodes are matted or if there is extracapsular extension, the prognosis is still worse.

When there is distant metastasis, the cancer is generally considered incurable. The five year survival rate is less than 10%. The median survival is 6 to 12 months. Treatment is palliative, focusing on life-extension and quality of life. In some cases, patients may live many months or even years with metastatic melanoma (depending on the aggressiveness of the treatment). Metastases to skin and lungs have a better prognosis. Metastases to brain, bone and liver are associated with a worse prognosis.

There is not enough definitive evidence to adequately stage, and thus give a prognosis for ocular melanoma and melanoma of soft parts, or mucosal melanoma (e.g. rectal melanoma), although these tend to metastasize more easily. Even though regression may increase survival, when a melanoma has regressed, it is impossible to know its original size and thus the original tumor is often worse than a pathology report might indicate.

Staging

Further context on cancer staging is available at TNM.

Stage 0: Melanoma in Situ (Clark Level I), 100% Survival

Stage I/II: Invasive Melanoma, 85-95% Survival

T1a: Less than 1.00 mm primary, w/o Ulceration, Clark Level II-III
T1b: Less than 1.00 mm primary, w/Ulceration or Clark Level IV-V
T2a: 1.00-2.00 mm primary, w/o Ulceration

Stage II: High Risk Melanoma, 40-85% Survival

T2b: 1.00-2.00 mm primary, w/ Ulceration
T3a: 2.00-4.00 mm primary, w/o Ulceration
T3b: 2.00-4.00 mm primary, w/ Ulceration
T4a: 4.00 mm or greater primary w/o Ulceration
T4b: 4.00 mm or greater primary w/ Ulceration

Stage III: Regional Metastasis, 25-60% Survival

N1: Single Positive Lymph Node
N2: 2-3 Positive Lymph Nodes OR Regional Skin/In-Transit Metastasis
N3: 4 Positive Lymph Nodes OR Lymph Node and Regional Skin/In Transit Metastases

Stage IV: Distant Metastasis, 9-15% Survival (10-Year Survival ~0%)

M1a: Distant Skin Metastasis, Normal LDH
M1b: Lung Metastasis, Normal LDH
M1c: Other Distant Metastasis OR Any Distant Metastasis with Elevated LDH

Based Upon AJCC 5-Year Survival With Proper Treatment

Treatment

Treatment of advanced malignant melanoma is best performed from a multi