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INTRODUCTION

The histopathological recognition of the exceptionally diverse benign, intermediate, and malignant cutaneous melanocytic lesions and their differential diagnoses remain formidable challenges to pathologists (Table 27-1). The gravitas of the diagnostic problem rests with the potential lethality of cutaneous melanoma, the phenomenon of occasionally delayed metastases after a latency of 15 to 25 years or more, the current absence of fully curative treatments for advanced melanoma, and the frequent curability of early melanoma by surgical excision. The reasons for the inordinate difficulty of melanocytic lesions relate to the profound lack of knowledge about their biological nature, the considerable heterogeneity and clinicopathological mimicry of melanoma and nevi one to the other, and consequently the lack of reliable criteria for discriminating melanoma from other melanocytic (and sometimes nonmelanocytic) lesions in a proportion of cases. The goals of this chapter are (1) to provide histopathologic and other criteria for the interpretation of melanocytic lesions following a pragmatic approach to interpretation so that melanoma is recognized if possible but not overdiagnosed, and (2) at the same time ensure that other biologically significant melanocytic neoplasms are not neglected but rather are managed appropriately.

Table 27-1Classification of Melanocytic Tumors

CIRCUMSCRIBED PIGMENTED LESIONS COMPOSED OF BASILAR MELANOCYTES

Solar lentigo

Synonyms: Lentigo senilis, liver spot, “ink spot” lentigo.

Solar lentigo (SL) occurs on sun-exposed skin1,2 in more than 90% of the white population older than age 60 years but may be observed in much younger individuals as well.1 Solar lentigines are distinguished from common freckles by their persistence despite absence of sun exposure. Solar lentigines are prominent in xeroderma pigmentosum. ...

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