Tumors arising in nevus sebaceus: A study of 596 cases

Prophylactic surgical excision of nevus sebaceus (NS) during childhood is often recommended because various neoplasms can occur on NS. The proportion of malignant tumors occurring on NS is highly variable among the published series, and there are controversies on the nature of these neoplasms because many of the previously described basal cell carcinomas could actually be trichoblastomas, which are benign follicular tumors.

We retrospectively analyzed all cases of NS of our collection, excised during the period from 1932 through 1998, and recorded all associated epithelial and nonepithelial changes. We especially differentiated basal cell carcinomas from trichoblastomas by silhouette analysis and examination of the stroma. These findings were analyzed according to gender, age, and localization.

Microscopic analysis of NS by two examiners was performed independently of clinical data.

A total of 596 cases were included from 290 females and 306 males, mean age 25.4 years (range, 1 month to 87 years); 232 were excised in children younger than 16 years. NSs were located on the scalp in 49.8% of cases. Basal cell carcinomas were found in 5 cases (0.8%, mean age 39.3 years) and benign tumors in 81 cases (13.6%, mean age 46.3 years). Syringocystadenoma papilliferum (n = 30, 15 males, 15 females) and trichoblastoma (n = 28, 7 males, 21 females) were the most frequent benign tumors. NS with associated tumors were located on the scalp in 79% of cases. Only 4 benign tumors (1.7%) and 2 warts were observed in patients younger than 16 years. Various types of epithelial hyperplasia were noted that could not be considered neoplasms, as well as epidermal and apocrine cysts.

The rate of malignant tumors arising on NS was very low and we did not observe such cases in children, who had associated benign tumors in only 1.7% of cases. Benign neoplasms were common and most of them occurred on the scalp; this was not a bias resulting from a longer duration before surgery. Trichoblastoma and not basal cell carcinoma was the most frequent follicular tumor associated with NS and showed a striking female predominance. Most trichoblastomas had previously been misdiagnosed but could actually be easily recognized by typical histologic features. Because most tumors occurred in adults older than 40 years, our study suggests that prophylactic surgery in young children is of uncertain benefit. Clinical follow-up is probably sufficient, and even those cases with clinical changes often proved to be benign tumors or warts.