| disease | Malignant Melanoma |
| alias | Evil Black, Malignant Melanoma |
Malignant melanoma (abbreviated as MM) is a malignant tumor originating from melanocytes, mostly occurring in the skin, and ranks third in the incidence of skin malignancies.
bubble_chart Etiology
Not entirely clear. Sunlight exposure is a dangerous factor, especially for Caucasians whose skin is excessively exposed to sunlight, making them more prone to this disease. Local trauma stimulation is also a common cause. Additionally, it is related to the malignant transformation of pigmented nevi, with some statistics showing it accounts for about 10%. Other possible contributing factors include genetics, low immune response in patients, and viral infections.
bubble_chart Pathological Changes
The typical pathological features of malignant melanoma include atypical melanocyte proliferation at the dermo-epidermal junction, with tumor cells invading both the epidermis and dermis. The tumor cells exhibit biphasic differentiation, consisting of epithelioid and spindle cell types. The nuclei show significant atypia with bizarre shapes. Mononuclear, binuclear, or multinuclear cells may also be observed, and mitotic figures are common.
The histopathological morphology of malignant melanoma varies depending on the type.
1. Malignant freckle-like nevus melanoma: The epidermis is atrophic, with numerous atypical melanocytes in the basal layer that invade the dermis. Melanophages containing abundant melanin are present within or between the tumor cells.
2. Superficial spreading melanoma: The epidermal rete ridges show irregular downward hyperplasia. Atypical nevus cell nests are visible at the dermo-epidermal junction and within the dermis. In addition to epithelioid and spindle-shaped melanocytes, a few Paget-like melanocytes may be seen in the upper epidermis. The dermis exhibits significant inflammatory cell infiltration.
3. Nodular melanoma: Atypical melanocytes proliferate vertically downward into the dermis without invading the epidermis. Epithelioid melanocytes often arrange in an alveolar pattern, while spindle-shaped cells resemble fibroblasts and may form bundles.4. Acral freckle-like nevus melanoma: The epidermis is thickened, with nests of atypical melanocytes containing abundant pigment located in the lower epidermis. Spindle-shaped melanocytes are common, and Paget-like melanocytes may also be seen in the upper epidermis. Melanophages are present in the dermal papillae.
Amelanotic malignant melanoma exhibits the characteristic cellular morphology of melanoma, but no obvious melanin is visible with HE staining. The Dopa test may yield a positive reaction, and silver staining can reveal small amounts of melanin.
In addition to diagnosis and typing, the histological assessment of malignant melanoma should evaluate the depth of invasion, as deeper tumor cell infiltration correlates with a poorer prognosis. Two main parameters, Clark's level and Breslow thickness, are commonly used.
(1) Clark's levels: Level I: Tumor cells are confined to the epidermis; Level II: Invasion into the papillary dermis; Level III: Filling the papillary dermis; Level IV: Invasion into the reticular dermis; Level V: Invasion into the subcutaneous fat layer. The 5-year survival rates from Level I to Level V are 99%, 95%, 90%, 65%, and 25%, respectively.
(2) The Breslow measurement method uses an ocular micrometer to measure tumor thickness. The relationship between tumor thickness and 5-year survival rate is as follows: less than 0.85 mm: 98%; 0.8–1.69 mm: 90%; 1.7–3.59 mm: 70%; greater than 3.6 mm: 45%.
1. Lentigo maligna melanoma develops from lentigo maligna, typically after many years, with the rash expanding and the appearance of blue-black nodules and ulcers, commonly seen on the faces of elderly individuals.
2. Superficial spreading melanoma is more common in Caucasians. The rash presents as irregular pigmented patches in red, white, or blue, with uneven edges and a bumpy surface, where small raised nodules can be felt.
3. Nodular melanoma can occur anywhere on the body and progresses rapidly. It begins as brown-red, blue, or black subcutaneous nodules, which may ulcerate and bleed. A characteristic feature is satellite lesions or pigment leakage. Early lymph node metastasis and hematogenous spread are common.
4. Acral lentiginous melanoma accounts for about 5% of all melanomas but is more prevalent in Black and Asian populations. Reports in China also indicate this type as common. It starts as a slowly spreading irregular pigmented patch, resembling lentigo maligna in color variation. Eventually, the rash develops into nodules and ulcers, mostly occurring on the palms and soles, particularly the soles. Subungual and periungual areas are also frequently affected.
In addition to the above types, amelanotic malignant melanoma may also be observed.
All suspicious black lesions, as well as pre-existing pigmented nevi that show enlargement, darkening, redness, bleeding, or ulceration, should be completely excised for histopathological examination. When a lesion carries the risk of dissemination, biopsy should be avoided to prevent early metastasis. If conditions permit, frozen-section rapid pathological examination is preferable. Once diagnosed, wide excision should be performed immediately.
bubble_chart Treatment Measures
For early, non-metastatic nodular or patchy lesions, surgical excision should be performed, including 1–3 cm of normal tissue around the lesion. If it involves a finger or toe (malignant melanoma), amputation is necessary. Confirmed affected lymph nodes should be removed, but prophylactic lymph node dissection remains controversial. Isolated limb perfusion with antimitotic drugs also shows some efficacy in treating limb melanoma. For cases with extensive hematogenous metastasis, a combination chemotherapy regimen based on dacarbazine and radiation therapy should be adopted.
