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Benign epithelial tumors, hamartomas, and hyperplasias comprise a large and disparate group of tumors and no single classification system unifies them, as their cells of origin and clinical presentation can vary substantially. In this chapter, the clinical entities are grouped by clinical or histologic features to better present them from a practical diagnostic and treatment perspective (Table 118-1).

Table 118-1 Overview
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Seborrheic Keratosis at a Glance
  • Seborrheic keratosis is the most common benign epidermal tumor.
  • Usually begin as well-circumscribed, dull, flat, tan, or brown patches with pseudohorn cysts.
  • Rapidly growing, symptomatic, or atypical lesions should be biopsied to rule out malignancy such as basal cell carcinoma, squamous cell carcinoma, or melanoma.
  • Clinical and histopathologic variants include the common seborrheic keratosis, reticulated seborrheic keratosis, stucco keratosis, clonal seborrheic keratosis, irritated seborrheic keratosis, seborrheic keratosis with squamous atypia, melanoacanthoma, and dermatosis papulosa nigra.
  • Hallmark histopathologic findings: acanthosis, papillomatosis, pseudohorn cysts, hyperkeratosis.
  • Internal malignancy: individuals can develop multiple, eruptive seborrheic keratoses (Leser–Trélat sign). Adenocarcinoma of the stomach is most common associated malignancy.

Seborrheic keratoses (SKs) are the most common benign epidermal tumor of the skin and a frequent focus of patient concern because of their variable appearance. These lesions are common in middle-aged individuals and can arise as early as adolescence.1 Although there are many clinical variants of the lesions, these lesions usually begin as well-circumscribed, dull, flat, tan, or brown patches. As they grow, they become more papular, taking on a waxy, verrucous, or stuck-on appearance (Figs. 118-1 and 118-2). Many lesions display distinctive pseudohorn cysts that likely represent plugged follicular orifices. SKs may arise on any nonmucosal surface, and multiple lesions may be distributed in a Christmas tree pattern along skin folds or in Blaschko's lines.2 The color of these lesions ranges from pale white to black. At times, distinguishing these lesions from a nevus or melanoma can be clinically challenging. Because melanoma, basal cell carcinoma, and other cutaneous malignancies have been reported to arise in SKs, care must be taken to critically evaluate rapidly growing, symptomatic, or unusual lesions.3,4

Figure 118-1

Seborrheic keratosis (basal cell papilloma) showing lackluster surface and stuck-on ...

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