melanoblastoma


Also found in: Dictionary, Thesaurus, Encyclopedia.

melanoma

 [mel″ah-no´mah]
a tumor arising from the melanocytic system of the skin and other organs. When used alone, the term refers to malignant melanoma.
acral-lentiginous melanoma an uncommon type of melanoma, although it is the most common type seen in nonwhite individuals, occurring chiefly on the palms and soles, and sometimes involving mucosal surfaces, such as the vulva or vagina. The characteristic lesion is an irregular, enlarging black macule, which has a prolonged noninvasive stage.
lenti´go malig´na melanoma a cutaneous malignant melanoma found most often on the sun-exposed areas of the skin, especially the face. It begins as a circumscribed macular patch of mottled pigmentation, showing shades of dark brown, tan, or black (lentigo maligna or melanotic freckle of Hutchinson), and enlarges by lateral growth before dermal invasion occurs. This type seems to be the least aggressive form of malignant melanoma.
malignant melanoma a malignant skin tumor, usually developing from a nevus and consisting of dark masses of cells with a marked tendency to metastasis. It is not common, but its incidence is increasing and it is the most aggressive type of skin cancer. It arises from pigment- (melanin-) producing cells and varies in course and prognosis according to type; types include superficial spreading melanoma, nodular malignant melanoma, and lentigo maligna melanoma. In general, the superficial lesions can be cured by surgical excision of the mole and adjacent tissues. Deeper lesions tend to metastasize rapidly through the lymphatic and circulatory systems. In some cases the condition has a genetic component. Early detection and skin protection are key in its control.

melanoblastoma

/mel·a·no·blas·to·ma/ (mel″ah-no-blas-to´mah) malignant melanoma.

melanoblastoma

[mel′ənō·blastō′mə]
a tumor of poorly differentiated melanin-producing cells.

melanoma

A tumour that comprises 1–3% of all new cancers (18,000/year) and causes 6500 deaths/year (US), most age 30–50; melanoma is increasing at ± 7%/year, and now affects 9/105 (primarily the head and neck) in men and 12/105 (primarily legs) in women; it is rare but more aggressive in children.
 
Risk factors
Giant congential melanocytic nevus, dysplastic nevus, xeroderma pigmentosum, immunodeficiency, moles with persistent pigment changes (especially > age 15), large or irregularly pigmented lesions, familial moles, congenital moles, Caucasian (12-fold greater risk than Black), previous melanoma, melanoma in 1st-degree relative, immunosuppression, photosensitivity, increased sun exposure.
 
Site of metastasis
Liver, lung, intestine, pancreas, adrenal, heart, kidney, brain, spleen, thyroid.

Management
Wide excision; chemo- and radiation are essentially useless.
 
Prognosis
Local recurrence common; many metastasise; 5-year survival reflects stage when diagnosed. 

Poor prognostic factors
Large size, paranasal/nasopharyngeal location, vascular invasion, high mitotic activity, marked cellular pleomorphism, distant metastases.

Stages of melanoma
▪ Stage I—Confined to epidermis and/or upper dermis, and measures ≤ 1.5-mm thick.
▪ Stage II—1.5-mm to 4-mm thick; spread to lower dermis but not beyond or to adjacent lymph nodes.
▪ Stage III—Any of the following:
   – > 4-mm thick;
   – Spread beyond the skin;
   – Satellite lesions within 2 cms of the original tumour; or
   – Spread to nearby lymph nodes or satellite lesions between original and regional lymph nodes.
▪ Stage IV—Metastases to other organs or to lymph nodes far from the original lesion.

Types of melanoma
Acral lentiginous melanoma
A rare, flat, palmoplantar or subungual lesion more common in non-whites; average 5-year survival < 50%; unrelated to actinic exposure, but possibly related to ectopic pigmentation.
 
Amelanotic melanoma
Rare, poorly differentiated, and occurs in those with a previous pigmented melanoma; since the Fontana-Masson stain is rarely positive in amelanotic melanoma, special studies are necessary, including immunoperoxidase staining with antibodies to the S-100 antigen and ultrastructural examination for presence of premelanosomes.
 
Lentigo maligna
Comprises 10% of melanomas; affects those > age 60; appears as flat, indolent lesions on face, arising from a premalignant freckle with greater than 90% 5-year survival; aetiologically linked to prolonged actinic exposure.
 
Nodular melanoma
15% of cases; similar clinically to superficial spreading melanoma; 50% average 5-year survival.
 
Premalignant melanoma
1/3 of lentigo maligna (Hutchinson’s freckle) progress to malignant melanoma after 10–15 years.
 
Superficial spreading melanoma
70% of cases; affects ages 30 to 60, especially female in lower legs or trunk, as a flat lesion (radial growth phase) that may be present for months to years; average 5-year survival 75%; aetiologically linked to recreational actinic exposure.
 
Thin melanoma (Stage-I cutaneous melanoma)
A lesion measuring < 1 cm in diameter; virtually 100% survival.