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PART II
Soft Tissue Lesions
Although the etiology of melanoma is unknown, it is recognized that over exposure to ultraviolet light is a significant promotive factor. Several risk factors have been recognized 55 and are listed in the box below. Although many cutaneous melanomas arise from nonlesional nevi, a significant percentage develop from preexisting nevi. Specific changes in preexisting nevi suggest malignant change55 and are listed in the box at right. Most primary melanomas of the skin may now be classified as separate lesions on clinical, histologic, and behavioral bases; these include lentigo maligna melanoma, superficial spreading melanoma, nodular melanoma, and acral-Ientiginous melanoma. 55 The first three types are listed in ascending order of malignant behavior. The 5year survival rate for cutaneous melanoma is 84%.56
RISK FACTORS FOR CUTANEOUS MELANOMA • • • • • • • • •
Large number of typical moles Atypical moles Family history of melanoma Prior melanoma Freckling History of repeated blistering sunburns Ease of sunburning Inability to tan Light hair and blue eyes
Lentigo maligna melanoma has a predilection for the exposed surfaces of older patients. On clinical examination, it is seen as a pigmented macule with an ill-defined margin. During the first phase, it grows slowly in a radial (developing uniformly around a central axis) and superficial manner. This slow-growth phase usually continues for many years, and then behavior becomes more aggressive as the second phase begins. In this stage, invasion becomes advanced and metastasis frequent. 57 Prognosis for the lentigo maligna melanoma is considered to be good, particularly if it is completely excised during the radial-growth phase. Superficial spreading melanoma is the most common form of melanoma and shows some behavioral characteristics similar to lentigo maligna melanoma. It begins as a pigmented macule that enlarges slowly for several years in a superficial radial-growth pattern (Fig. 12-18). As the name implies, the superficial malignant melanocytes are restricted mostly to the epithelium and the junction. If the
SUSPICIOUS CHANGES IN NEVI • • • •
A-asymmetry B-border irregularity C-color variegation D-diameter greater than 0.6 mm
B
A
Fig. 12-18. Superficial spreading melanomas. A and B, Two views of a 'superficial spreading melanoma on
c
the maxillary ridge of a 45-year-old man. The patient had watched it slowly grow for several months. B, Mirror shot showing the spread of the tumor from the labial gingiva through the interproximal area to involve the lingual gingiva. C, Superficial spreading melanoma of the lower lip in a 59-year-old man that had been present for 8 years, spreading from two small, pigmented patches. Nodules were now present on the mucosal surface. (A and B from Robertson GR, Defiebre BK, Firtell DN: Primary malignant melanoma of the mouth. J Ora! Sl/rg 37:349-352, 1979. C from Regezi JA, Hayward JR. Pickens TN: Superficial melanomas of oral mucous membrane, Ora! Surg 45[5]:730-740, 1978.)