Subungual Eccrine Porocarcinoma: Rare but Possible

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A 73-year-old man presented with a 10-year history of an asymptomatic, slow-growing, subungual lesion of the right third toe. The lesion has been treated in the past as an onychomycosis and then as a wart without success. On physical examination, an erythematous, partly eroded lesion associated with onycholysis, was found on the third toe (Figure 1). The nail plate was partially destroyed. There was no inguinal lymphadenopathy. The clinical impression was between a squamous cell carcinoma, basal cell carcinoma, an achromic melanoma, and eccrine porocarcinoma. An incision biopsy was taken for histopathological diagnosis, which showed an eccrine porocarcinoma. The lesion was excised, but it relapsed after 8 months; so a new excision was performed. Surgical margins result involved so any other conservative intervention was precluded. Definitive treatment was made by a surgical amputation of the toe at the level of the first metacarpophalangeal joint. Histological examination of the amputated toe highlighted bone infiltration (Figure 2). Metastatic workup revealed normal findings.
Porocarcinoma is a rare malignancy of the acrosyringium, the intraepidermal portion of the eccrine sweat glands, that affects mostly elderly patients.1 Approximately 20% of porocarcinoma metastasize to regional lymph nodes, with 67% mortality rate, whereas distant metastasis arises in about 10% of patients. Local recurrence rate after surgical intervention is in the range of 11% to 20%.1 Treatment of choice for porocarcinoma is complete surgical excision with broad tumor margins and regional lymph node dissection if needed. There are anecdotal reports that show some benefits when using radiation, chemotherapy, or intralesional photodynamic therapy.2
To the authors' knowledge, in literature, there are only 3 reported cases of periungual porocarcinoma, in particular 2 in the fingers and 1 in the toe; so the localization of the authors' patients is very rare.3–5
Porocarcinoma is usually asymptomatic so patients tend to neglect it until it comes to a more advanced state or causes functional problems. In the early stages, the cancer may resemble many common benign conditions, such as onychomycosis and viral wart, as the authors' patient that was treated ineffectively for years.
For all these reason, identification and early diagnosis of eccrine porocarcinoma may be very difficult and challenging. An intervention of surgical amputation was needed in the authors' patient and the other 3 cases of periungual porocarcinoma of the literature needed it too,3–5 documenting the difficulty of diagnosis of this pathology. Despite the invasiveness, in the authors' patient, the amputation was decisive, not causing particular inconvenience because of its location on the foot.
Subungual porocarcinoma is a slow-growing but aggressive and potentially fatal skin cancer, but curable if accurately diagnosed and properly treated. An early diagnosis is crucial to ensure the best prognosis. With this report, the authors want to highlight that for physicians it is important to have a basic knowledge of this disease to start to consider porocarcinoma in the differential diagnosis especially of long-standing lesion of the extremities and head in elderly patients.
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