Basaloid neoplasms in nevus sebaceus

Background: Nevus sebaceus (NS) (organoider nevus) may frequently be associ ated with the development of a number of benign and malignant neoplasms amo ng which basaloid neoplasms are the most common. Histopathologic criteria f or diagnosis and classification of basaloid proliferations arising in NS ar e still debated. Most previous investigators have considered them to repres ent mainly basal cell carcinomas (BCCs). On the contrary, a number of recen t authors have proposed that most basaloid neoplasms in NS exhibit predomin antly morphologic features implying benignancy, thus representing trichobal stomas (TBs). In this study, we attempted to characterize better the histop athologic features of basaloid neoplasms in NS in a large series based on c urrent morphologic criteria. Methods: Three-hundred and sixteen cases of NS seen over 19 years were cons ecutively sampled and reviewed for basaloid neoplasms. Twenty-four cases of basaloid neoplasms in NS were identified and categorized based on current histopathologic criteria either as TB or BCC. For comparison of histopathol ogic features, 37 solitary TB were also studied. Results: Following histopathologic analysis, 22 cases were categorized as T B (91.6%, 10 males, 12 females; mean age 40.8 years, range 19-78 years) and 2 cases as BCC (8.4%, 1 male, 1 female; 32 years and 40 years). Clinical f eatures in both groups were generally similar. The lesions presented exclus ively on the head and neck as skin colored to pigmented papules or nodules within NS (scalp in 19 TB cases and 1 BCC case; face in 2 TB cases and 1 BC C case; neck in 1 TB case). Histopathologically, TB in NS were characterize d by smooth-bordered basaloid aggregations with either a nodular and/or a s uperficial pattern, abundant fibrous stroma with focal clefts within the st roma, and prominent features of limited follicular differentiation (rudimen tary follicular germs in concert with papillae). In contrast, BCC in NS sho wed basaloid aggregations that vary markedly in size and shape, scant fibro us stroma, focal mucinous clefts between basaloid aggregations and surround ing stroma, and lack of prominent rudimentary follicular germs in concert w ith papillae. Remarkably, sections in a few cases of TB showed features occ asionally found in BCCs but presently widely considered to be unspecific (e .g., ulceration, cystic degeneration, and focal clefts between basaloid agg regations and surrounding stroma). Two cases of TB in NS were associated wi th a sebaceoma and 1 case with a desmoplastic trichilemmoma. Follow-up data in 14 TB cases and 2 BCC: cases (mean follow-up 28.8 months; range 1 to 16 0 months) revealed no local recurrences or distant metastases. Conclusion: Our study confirms that the vast majority of the basaloid neopl asms arising in NS show clear-cut morphologic criteria for TB, whereas only a few cases display histopathologic features consistent with BCC. In a min ority of cases, basaloid neoplasms with overall morphologic features of TB may present problems in diagnosis when they exhibit a few histopathologic f eatures traditionally associated with BCC or when they occur in combination with other adnexal neoplasms.