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| Malignant Melanoma |
| Etiology •Malignant melanomas are pigmented, malignant lesions of usually skin origin, but may arise in other areas, particularly the eye. |
| Pathogenesis •Believed to be due to chronic exposure to the sun's UV rays., |
| Epidemiology •The incidence of malignant melanomas has steadily increased over the last several decades, perhaps due to the increase in the tendency of individuals to expose themselves to the sun. •It is primarily found in light-skinned individuals exposed to sun over prolonged periods of time and is particularly common in areas such as Australia. |
| General Gross Description •Grossly, a melanoma exhibits evidence of nodular growth in contrast to benign lesions which are either flush or a rounded, evenly nodular mass. •Unevenness of pigmentation, ranging from jet black to areas of complete depigmentation are also noted. •On the cut surface, the malignant melanoma can appear as a nodular mass that is replaced part of the epidermis, as well as extending as a grayish-white lesion into the dermis. •Significant changes in pigmentation within the tumor may be noticed from area to area; in extreme examples, the lesion may be completely unpigmented. •In the eye, melanomas appear grossly as grayish lesions that extend from the iris into the posterior chamber. •The variation in pigmentation is noticeable here as well. |
| General Microscopic Description •Histologically, the lesion is composed of proliferating nests and cords of melanocytes that show distinct variation in the size, as well as in the morphology of the nucleus. •A prominent eosinophilic nucleolus is one of the distinguishing features of a malignant melanoma. •Infiltration of melanocytes into the dermis, replacement of stretches of the basal layer of the epidermis by proliferating melanocytes, presence of necrosis and calcification are all hallmarks of a malignant melanoma. |
| Clinical Correlation •Evidence of darkening of an existing, flush lesion should alert the patient to the possibility of malignant transformation. •Presence of uneven nodularity, radial enlargement, changes in pigmentation or the appearance of a mass are all clinical signs of malignancy. •While considered to be of universally grim prognosis in the past, advances in our understanding of the biology has led to a considerable improvement in the overall prognosis of this condition. •Prognosis is dependent on depth of invasion. |
| References • Cotran RS, Kumar V, Robbins SL: Robbins Pathologic Basis of Disease. 5th edition. Philadelphia, W.B. Saunders, 1994, pp. 1179 • Harrison's Principles of Internal Medicine, 13th Edition: Isselbach et. al. (eds). New York, McGraw-Hill, 1994, pp. 1867 |
| Malignant Melanoma |
| Synopsis by: T.V.Rajan, M.D., Ph.D. (T01000M87203)[522] |
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