Eccrine Poroma Arising within Nevus Sebaceous

Nevus sebaceous (NS) is a congenital, benign, cutaneous hamartoma, which commonly occurs at birth and is located in the head and neck. It presents at first as well-demarcated skin-colored hairless plaques, and becomes more yellowish, thickening and verrucous at puberty1. Secondary neoplasms arising within NS can develop during adolescence and adulthood. One study found that 21.4% of lesions with NS developed secondary neoplasms; benign tumors accounted for 18.9%, whereas malignant tumors comprised the remaining 2.5%2. Trichoblastoma and syringocystadenoma papilliferum are the most common benign secondary neoplasms, while basal cell carcinoma is the most common malignant secondary neoplasm1. However, poroma arising within NS has rarely been reported.

A 28-year-old female with a hairless lesion on her scalp since birth complained of a soft mass that had developed on the lesion three to four years prior to presentation. Physical examination revealed a localized, 1 cm×2.5 cm-sized, yellowish to brownish, verrucous-surfaced plaque with a 1 cm×1 cm-sized pedunculated erythematous tumor on the scalp (Fig. 1). Skin biopsy was performed on both the plaque and tumor lesions. The histopathological evaluation demonstrated papillomatosis and acanthosis in the epidermis and numerous sebaceous and apocrine glands within the dermis of the plaque lesion. In addition, well-demarcated tumor nodules were noted in a downward proliferation toward the dermis composed of small cuboidal basaloid cells on the tumor lesion. The findings were consistent with NS and eccrine poroma, respectively. Surgical mass excision of the whole lesion was performed. Based on the histopathologic findings, the patient was eventually diagnosed with eccrine poroma arising within NS (Fig. 2).

Fig. 1
(A, B) Localized, 1 cm×2.5 cm-sized, yellowish to brownish, verrucous-surfaced plaque with a 1 cm×1 cm-sized, pedunculated, erythematous tumor on the scalp (we received the patient's consent form about publishing all photographic materials).

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Fig. 2
(A, B) The histologic findings were consistent with nevus sebaceous. (A) Papillomatosis and acanthosis were visualized in the epidermis, and numerous sebaceous glands and apocrine glands were observed within the dermis (H&E, ×40). (B) Numerous lobules of sebaceous glands were noted within the dermis without connection to the epidermis (H&E, ×100). (C, D) The findings were consistent with eccrine poroma. (C) Well-demarcated tumor nodules were found with a downward proliferation toward the dermis (H&E, ×40). (D) Tumor nodules composed of small cuboidal basaloid cells were also seen (H&E, ×100).

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First described by Goldman et al.3 in 1956, poroma is a benign adnexal tumor originating from an intraepidermal component of the sweat gland duct that was initially classified as a neoplasm originating from the eccrine gland. Apocrine poroma, first described in 1988 by Requena et al.4, shares many clinical similarities with eccrine poroma. More recent data suggest that apocrine components may be present as well5. Clinically, a poroma usually presents as a solitary, slow-growing, dome-shaped, painful papule or nodule commonly located on the palmar or plantar surface6. Involvement of the scalp is rare2. Poroma has been found to occur in patients with other skin diseases, and it can also develop within NS6. To the best of our knowledge, there are only six reported cases of poroma arising within NS (Table 1)1, 7, 8, 9, 10, 11.

Table 1
Previously reported cases of poroma arising within nevus sebaceous (NS)

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Among these reported cases, three were diagnosed as eccrine poroma, and three were found to be apocrine poroma. Apocrine poroma appears to occur at a higher rate in poroma originating from NS. In the apocrine poroma, the folliculosebaceous apocrine lineage shows homogeneous eosinophilic intraluminal secretion and lining cells with eosinophilic cytoplasm, the presence of sebaceous cells lined by poroid cells, and foci of follicular differentiation in the periphery6. In the present case, no folliculosebaceous apocrine lineage was visible, which is characteristic of eccrine poroma. If the histopathologic findings do not clearly distinguish between the two poroma types, immunohistochemical studies may be helpful. Immunohistochemical staining for epithelial membrane antigen (EMA) and carcinoembryonic antigen (CEA) on poroma reveal the following: apocrine poroma stains EMA negative or positive and CEA positive, but eccrine poroma stains EMA positive and CEA focally positive7, 8.

There have been a new hypothesis that has recently been studied, suggesting that eccrine gland is included in the pilosebaceous unit12. And in one study, eccrine gland hyperplasia was occured in 14% of NS lesion13. Therefore it might be thought that eccrine gland might be affected in NS.

Herein we report a rare case of eccrine poroma arising within NS. Although rarely documented in the literature, it should be considered as a secondary neoplasm within NS.