Diagnosis of Primary Melanoma

The melanoma family encompasses tumors with different clinical characteristics and biological behavior. Several classifications have been proposed, based on clinical features, histopathologic alterations, and different anatomic locations. In the current chapter, the selected classification is clinically oriented, aiming to follow the real scenarios that clinicians are faced with in their everyday practice: (1) conventional melanoma, subclassified into melanoma of the trunk and extremities, face, acral sites, nails, and mucosa; (2) nodular melanoma; and (3) amelanotic melanoma. As a rule, melanoma is characterized by a morphologic asymmetry, which is reflected in its overall shape, border, and color distribution. These characteristics have been summarized in the ABCD clinical rule, whose introduction and dissemination among clinicians terminated the era when melanoma was diagnosed as an ulcerated or bleeding tumor. Melanomas deviating from the ABCD criteria are much more difficult to diagnose and include nodular and amelanotic tumors. Therefore, clinicians should be very careful and lower the threshold for excision when evaluating nodular or amelanotic tumors. Dermoscopy significantly improves the diagnostic performance of clinicians, both by allowing the detection of clinically inconspicuous melanomas and by enabling the recognition of benign lesions that might look clinically worrisome, reducing, thus, the number of unnecessary excisions. The dermoscopic criteria of melanoma are a result of its asymmetric growth and vary among different subtypes of the disease. The “classic” dermoscopic criteria of melanoma are the following: atypical pigment network, irregular dots/globules, irregular streaks/pseudopods, irregular blotches, regression structures, blue-white veil, and atypical vascular pattern. In clinical practice, the majority of melanomas can be recognized by the presence of at least one of these criteria. However, dermoscopically “featureless” melanomas do exist and include very early tumors, but also nodular and amelanotic melanoma. Therefore, clinicians should be very careful when evaluating nodular and amelanotic lesions. Facial melanoma displays different dermoscopic characteristics and has to be differentiated from pigmented actinic keratosis and solar lentigo. Dermoscopy is useful also for the diagnosis of melanoma of specific anatomic sites including acral, subungual, and mucosal melanoma. Reflectance confocal microscopy (RCM) is a new noninvasive technique that allows to rapidly explore the skin at nearly histological resolution. Since its inception, RCM was applied mainly in the field of melanocytic lesions because melanin is the strongest source of contrast for this method. In skin oncology, RCM stands up as an add-on test for the diagnosis of melanoma being capable of improving the specificity of a narrow-selected population of dermoscopically equivocal lesions. For clinicopathological purposes, it is still useful to refer to the classification proposed by Clark (the United States) and McGovern (Australia) where categories are identified by the microscopic features of the intraepidermal component of the neoplasm.