This paper presents a case of malignant hidroacanthoma simplex (HAS) and review the literature of previous cases to summarize the histopathological and immunohistochemical features and display the dermoscopic features of malignant HAS.

We present an 88-year-old Asian female with malignant HAS. The diagnosis was made according to the histopathological and immunohistochemical results after biopsy. Previous case reports of malignant HAS were retrieved from PubMed to characterize the histopathological and immunohistochemical features. We also display the dermoscopic features of malignant HAS that have not been reported.

Our findings demonstrate that prompt surgical treatment is an effective strategy for malignant HAS. Histopathology and immunohistochemistry are valuable diagnostic tools. This is the first case report to display the dermoscopic features of malignant HAS, and we speculate that dermoscopy may contribute to the diagnosis of malignant HAS.

Hidroacanthoma simplex (HAS) is a rare benign tumor that is also known as intraepidermal poroma. While there have been a few reports of HAS with malignant transformation (porocarcinoma), we report an unusual case of porocarcinoma, arising in a pigmented HAS, the latter also showing secondary amyloid deposits. An 80-year-old Japanese man presented with a cutaneous tumor on his left buttock, which had first been noticed in his childhood. The tumor consisted of flat pigmented plaque and a depigmented papule with erosion. Histologic analysis revealed many pigmented and well-defined nests within the epidermis of the flat pigmented portion. The nests were composed of cuboidal to oval and occasionally elongated, bland, basaloid cells with numerous melanin granules. In addition, there were infrequently ductal structures and small clusters of sebocytes, and abundant amyloid deposits in the upper dermis. These findings were consistent with pigmented HAS with amyloid deposition. In the depigmented portion, markedly atypical cells with occasional ductal structures and intracytoplasmic lumina extended throughout the entire thickness of the epidermis, with minimal invasion of the dermis. We considered this portion of the tumor to be a porocarcinoma. Since the two portions of the tumor were continuous, we made a final diagnosis of porocarcinoma arising in pre-existing pigmented HAS with amyloid deposition.

Hidroacanthoma simplex (HAS) is an uncommon eccrine neoplasm of the skin. It is a benign neoplasm, but some cases of malignant change were reported in the literature.

To describe a rare case of porocarcinoma in a relatively short period from pre-existing HAS on the abdomen.

Wide local excision was performed on this neoplasm.

There was no recurrence for 72 months after wide excision. CONCLUSION. : We recommend an early excision and careful attention in the case of HAS because of its potential malignant change.

Hidroacanthoma simplex is a benign tumor of the skin originating from or showing differentiation to the sweat glands. It grossly resembles seborrheic keratosis of Bowen's disease and histologically shows intraepidermal focal growth of epithelial cells. Malignant transformation of this tumor is rare. We report a case of pigmented hidroacanthoma with malignant transformation in a 67-year-old woman. There was a 20-year history of a skin lesion on the right thigh, which first appeared as a small verrucous papule, progressed to a dark-brown colored patch, and then to a pigmented plaque. Histologically, the primary tumor was composed of small squamoid cells with marked cellular atypia. Most of the tumor cells were located in the epidermis. Immunohistochemically, the cytoplasm of some tumor cells showed a positive reaction for epithelial membrane antigen, but not for either carcino-embryonic antigen or the S-100 protein.

There are many conditions characterized by nests of cells within the epidermis. One of them, hidroacanthoma simplex, has been regarded as an epidermal tumor differentiating to intraepidermal eccrine duct cell. We report a case of hidroacanthoma simplex with the results of immunohistochemical study. Staining for 35 beta H11 (reacting with keratin No. 8), 35 beta E12 (reacting with keratin No. 1, 5, 10, 11), S-100 protein, and CEA was negative in the tumor cell nests; these monoclonal antibodies stained the nests of eccrine poroma.

Argyrophil nucleolar organizer regions (AgNORs) were counted and immunostaining using antibodies raised against proliferating cell nuclear antigen (PCNA) and Ki-67 was carried out on eccrine acrospiroma and eccrine sweat gland carcinoma, to determine the malignant potential and prognosis of these tumours. Formalin-fixed and paraffin-embedded tissue specimens surgically excised from 25 patients with eccrine sweat gland carcinoma (20 cases of eccrine porocarcinoma, four cases of ductal sweat gland carcinoma and one case of malignant clear cell hidradenoma) and 25 patients with eccrine acrospiroma (16 cases of eccrine poroma, four cases of poroid hidradenoma and five cases of clear cell hidradenoma) were used. PCNA and Ki-67 labelling indices were categorized semiquantitatively into four grades. Significant differences were noted between eccrine sweat gland carcinoma and eccrine acrospiroma with these three methods (P < 0.01). When a cut-off of 5 was chosen, the AgNOR value distinguished eccrine sweat gland carcinoma from eccrine acrospiroma with high specificity and sensitivity. Moreover, we compared the results of these three methods between stages 1 or 2 (17 cases) and stage 3 (eight cases) eccrine sweat gland carcinomas, and no significant differences were observed. From these findings, these three methods are useful in discriminating malignant from benign lesions of eccrine tumours, but have no value in estimating the aggressiveness of eccrine sweat gland carcinomas.