Perforating elastic fibers (‘elastic fiber trapping’) in the differentiation of keratoacanthoma, conventional squamous cell carcinoma and pseudocarcinomatous epithelial hyperplasia

Abstract

Keratoacanthoma (KA), an epithelial neoplasm occurring in sun-exposed skin of the elderly, is considered a well-differentiated form of conventional squamous cell carcinoma (SCC) that often follows a course of spontaneous regression. Distinguishing KA from conventional SCC or pseudocarcinomatous epithelial hyperplasia ensures proper diagnosis, treatment and management. For some time, perforating elastic fibers have been utilized in differentiating KA from SCC. This phenomenon may also occur in association with scars and hypertrophic lupus erythematosus (LE). To assess the diagnostic utility of perforating elastic fibers, we compared their incidence in KA, SCC, scars with overlying pseudocarcinomatous hyperplasia, hypertrophic LE, hypertrophic lichen planus (LP) and lichen simplex chronicus (LSC). A retrospective case search identified 359 lesions and the presence of perforating elastic fibers was evaluated using routinely stained sections. This phenomenon was documented in all studied groups except hypertrophic LP. The incidence was found to be 71% in KA, 37% in SCC, and was lowest in inflammatory conditions with associated pseudocarcinomatous hyperplasia (hypertrophic LP 0%, hypertrophic LE 5.9% and LSC 28.2%). The observed frequency in pseudocarcinomatous hyperplasia overlying scars (57.8%) vs. KA (71%) was not statistically different. Although elastic fiber trapping has potential value as a diagnostic criterion for KA, dermatopathologists should consider its limitations. Its diagnostic utility was greatest in distinguishing KA from hypertrophic LE and hypertrophic LP. Conversely, elastic trapping is not helpful differentiating pseudocarcinomatous hyperplasia from recurrent/persistent KA following surgery.

Hypertrophic lichen planus mimicking squamous cell carcinoma: The importance of clinicopathologic correlation

“…Histologic features suggestive of HLP include hyperorthokeratosis, wedge-shaped hypergranulosis, and psoriasiform hyperplasia of the epidermis 5 ; lichenoid interface dermatitis with eosinophils 10 ; presence of typical features of PEH; and absence of cytologic atypia, marked solar elastosis, deep extension beyond the superficial dermis, and lymphovascular or perineural invasion 2, 3. Elastic staining to visualize the presence or absence of perforating elastic fibers may assist in distinguishing between SCC and HLP; perforating elastic fibers are rarely present in HLP but may be seen in SCC 11, 12…”

Acantholytic squamous cell carcinoma is usually associated with hair follicles, not acantholytic actinic keratosis, and is not “high risk”: Diagnosis, management, and clinical outcomes in a series of 115 cases

“…Moreover, acantholysis has been documented in other variants of SCC, including follicular SCC, 21 spindle-cell SCC, 22,23 and even rarely as an incidental finding in keratoacanthoma (KA), 24 despite the fact that some investigators definitionally exclude KA if acantholysis is present. 25 Cassarino and colleagues, 1 in their comprehensive review of the histopathology of cutaneous SCC, characterized aSCC as exhibiting intratumoral acantholysis “At least focally, but often extensively....” In the largest series to date, Johnson and Helwig 16 noted that aSCC tumors typically arose from the upper portion of follicular outer root sheath, but characteristic involvement of follicular epithelium was not mentioned in subsequent descriptions of aSCC 11,26 or follicular variants of SCC. 21,27,28 Of note, Carr and coworkers 29 identified a central acantho lytic mucin pool in over half of their series of 30 cases of follicular SCC and contrasted this finding with the characteristic suprabasilar acantholysis that typifies aAK and aSCC.…”

Transepidermal elimination of mucin is a very common but not yet reported phenomenon in digital myxoid cysts: a study of 35 cases

“…The nature of these elements varies in literature. Examples include pilomatricomas, follicular cysts, granuloma annulare, elastic fibers, collagen, leishmanias, foreign‐body type granulomas, carcinomatous cells or amyloids…”