Malignant melanoma occurs in several distinct clinical settings. In each of these settings the melanoma has a different clinical appearance, histologic pattern, and prognosis. These various types of melanoma are grouped together because they share common color changes, a common cell of origin, and the important biologic trait of progressive, inexorable growth and eventual metastasis.
Diagnostic Hallmarks
- Distribution: pattern variable with type of melanoma
- Irregular, jagged margination
- Asymmetric, non round shape
- Irregular pigmentation
- History of change in size or color
- Red, white, and blue hues within the lesion (superficial spreading melanoma only)
Clinical Presentation
Superficial Spreading Melanoma. This tumor, the most common of melanomas, presents as a relatively flat-topped, slowly growing, pigmented papule or small plaque. It is characterized by the following features. First, the lesion generally has an irregular or jagged margin. Second, the shape of the lesion is often asymmetric rather than being perfectly round. These first two characteristics presumably occur as the result of differential growth rates in various parts of the lesion. Third, the lesion is usually irregularly pigmented with small flecks of black speckling throughout the lesion. Fourth, there are frequently distinct areas of red, white, or blue color. Fifth, the lesion is almost always wider than it is tall. This occurs because there is a long period of horizontal (centrifugal) growth before appreciable vertical growth (invasion) begins. Sixth, in larger, more advanced lesions the surface has a somewhat “bumpy” or lobulated appearance because of the same differential growth rates that resulted in the development of an irregular border. Seventh, there may be pigment spread (”bleeding of pigment”) from the periphery of the lesion onto the normal adjacent skin. Eighth, nearly all melanomas are 7 mm or more (the width of a standard pencil eraser) in diameter. Ninth, subjectively (and the least useful of the criteria for diagnosis), the patient will sometimes indicate that the lesion has changed in one or more ways.
Superficial spreading melanomas are most commonly found on sun-exposed areas of skin. In men the back is the area most frequently involved, whereas in women the legs are the most common site. Interestingly, superficial spreading melanomas are almost never found on the face and dorsal hands ill spite of the heavy sunlight exposure received in these sites. lucause this type of melanoma is asymptomatic and grows so slowly, it is often serendipitously identified during routine examination for other medical reasons.
Nodular Melanoma. Nodular melanomas appear as domeshaped, darkly pigmented papules or nodules. They grow considerably faster and develop a deeper color than superficial spreading melanomas. Nodular melanomas, in contrast to superficial spreading melanomas, are also more evenly pigmented, are as tall as they are wide, and tend to have a Smooth rather than lobulated surface. Changes that occur in well-advanced lesions include the spread of pigment on to surrounding skin, the presence of satellite papules, and the development of an erosion or ulcer on the surface of the tumor.
Amelanotic variants of nodular melanoma can occur but are rarely seen. Such lesions simulate the appearance of pyogenic granulomas because of their reddish color but otherwise are clinically similar to the pigmented variety.
Nodular melanomas are unrelated to chronic sunlight damage and thus may be seen on any portion of the body. In darkly pigmented people they are particularly common on the soles of the feet.
Lentigo Maligna Melanoma. These lesions are found almost exclusively on the face of elderly adults. They arise from a preexisting lentigo (lentigo maligna) and thus appear as one or more small darkly pigmented and only slightly elevated papules superimposed on a flat, light-brown patch. The black, smooth-surfaced papular component has all the physical characteristics of a nodular melanoma except that they are smaller in size and grow more slowly.
Acrolentiginous Melanoma. This is the least common variant of melanoma. It consists of one or more dark, smooth papules appearing against a background of gray or black macular, unevenly speckled pigmentation. It is the usual type of melanoma occurring on the digits and on the palms and soles. Although it shares some clinical features with lentigo maligna melanoma, it appears to have a faster growth rate and overall poorer outcome.
For all practical purposes, the melanomas described above occur only after the age of puberty. A rapidly growing, pigmented papule in a child will, on biopsy, usually turn out to be a benign spindle and epithelioid cell nevus (Spitz nevus).
Course Prognosis
The outlook for patients with melanoma depends on several interrelated factors, such as the clinical type of lesion, the presence or absence of lymphadenopathy, and the histologic level of dermal invasion. For example, patients with a lentigo maligna melanoma usually present with a 5- to 10-year history of slow growth and are unlikely to have palpable regional nodes. Histologically, the lesion is likely to be quite superficial. On the other hand, superficial spreading melanomas when first recognized have usually been present for 2 to 5 years, lymphadenopathy is only occasionally present, and histologically, the lesions are usually either superficial or intermediate in depth. Finally, nodular melanomas are usually noted by the patient within the first 6 to 12 months of appearance. Lymphadenopathy is frequently present, and histologically, the lesions are often deeply invasive.
Among the factors, the one that most closely correlates with prognosis is the histologic depth of invasion at the time of biopsy. This is best determined by micrometer measurement of the thickness of the tumor (Hreslow technique). Thus, 5-year survival rates for patients with tumors less than 0.75 mm in thickness are better than ()S%. Rates for those with tumors 0.75 to 1.5 mm in thickness arc about 75% to 85%, and rates for those with tumors thicker than 1.5 mm are approximately 50% to 60%.
The prognosis for patients in these last two groups can he further refined, based on the status of their regional lymph nodes. The presence of microscopic metastases in more than one or two nonpalpable nodes reduces the survival rate by at least 20%. The presence of palpable nodes (regardless of the depth of the primary lesion) reduces the long-term survival.
It should recognized that melanoma at times can be very slow following and that it is the malignancy with the highest rate of spontaneous regression. Moreover, there have been many individual case reports of patients who have lived with metastatic disease for exceptionally long periods of time.
Pathogenesis
During the past 30 years, the incidence of melanoma has approximately doubled each decade. Most of this increase has been due to larger numbers of superficial spreading melanomas. This type of melanoma occurs primarily on the sun-exposed skin of people who tan poorly. However, in contrast to the situation with other types of skin cancer where total lifetime exposure appears critical, the risk for melanoma may be more closely related to the number and severity of individual episodes of sunburn, especially in the childhood years.
Genetic factors may also play a role in the pathogenesis of melanomas. About 10% of patients have a positive family history for melanoma. This genetic predisposition is most marked in the dysplastic nevus syndrome where an astonishingly large proportion of family members develop melanomas.
A third predisposing factor revolves around the presence of certain congenital nevi. Thus, a patient with a giant hairy congenital nevus has a risk of developing a melanoma that may be 100 times greater than the risk to those with ordinary acquired nevi.
A fourth factor relates to the presence of immune responsiveness. Those persons with either innate or iatrogenic reduction in immune responsiveness appear to be at increased risk for the development of melanomas, even as they are for the development of other types of malignancy.
Finally, hormonal factors may also be important. Men have an increased incidence of melanomas and also have a considerably poorer prognosis when compared with women having similar types of lesions.
Therapy
Therapy is based primarily on tumor thickness. Lesions thinner than 0.75 mm require only wide local resection. Historically, margins of 3 to 5 cm have been obtained, but current guidelines suggest that1.0- to 2.0-cm margins are entirely adequate. Lymph node metastases rarely occur in these thin lesions, and thus prophylactic lymphadenectomy is not routinely carried out.
Lesions with a thickness of 0.75 to 1.5 mm are handled more aggressively. Local recurrences are relatively common, and thus margins of 2 to 3 cm are desirable. Palpably enlarged lymph nodes are removed with en bloc excision where possible. No consensus is available regarding the necessity of regional lymphadenectomy in tumors of this thickness when nodes are not palpable. Microscopic metastases are found about 20% of the time when nonpalpable nodes are removed, but patients having only one or two nodes with involvement seem to have a prognosis as good as that for those without microscopic metastases.
Tags:acrolentiginous melanoma, Lesions, malignant melanoma, melanomas, nodular melanoma, papule, pigmentation plaque
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