EPC is a rare skin appendage tumor, with the main incidence occurring in patients more than 60 years old. The lower limbs are the most common site (44%), followed by the trunk (24%), head (18%), upper limbs (11%), and neck (3%)2
. The scrotum is an extremely uncommon primary location in that only 2 such cases have been reported in the international medical literature4,5
. EPC tends to be localized; however, it sometimes spreads to regional lymph nodes or adjacent skin, and it rarely metastasizes to distant organs or distant lymph nodes. Distant visceral metastases to the lung, retroperitoneum, long bones, breast, liver, mediastinum, urinary bladder, and ovary have been reported4,6
. Clinical features of EPCs reported in Korea to date are summarized in 3,7-16
. According to Shaw et al.17
, all 27 cases of EPC arose from a benign eccrine poroma (BEP); however, Robson et al.2
reported occurrence of EPC in only 18% of cases of BEP. In our view, skin manifestations of our patient developed de novo
because there was no preexisting lesion on the scrotum as well as on the pelvic area. In addition, EPC that arises from BEP usually shows very slow progression. This patient was relatively young and his disease showed an aggressive clinical course; the tumor developed primarily on the scrotum and showed rapid metastasis to multiple internal organs.
Summary of reported cases of eccrine porocarcinoma in Korean literature
The histopathologic features of EPC are broad. Malignant cells usually have large and hyperchromatic nuclei. Nuclear atypia with frequent mitoses and necrosis are characteristic. Cords and nests of polygonal tumor cells penetrate to the adjacent dermis or extend into subcutaneous tissue. Histopathologically, metastatic adenocarcinoma, trabecular carcinoma, and Merkel cell carcinoma should be included in the differential diagnosis. Distinguishing EPC from metastatic adenocarcinoma, and especially adenocarcinoma of a breast or lung origin, can be difficult. However, most metastatic adenocarcinomas are positive for EMA and CEA stains. Furthermore, a positive reaction with CEA may be most helpful in differentiating between primary and secondary lesions18
. In the present case, the negative reaction with CEA, the connection between the epidermis and tumor, and the absence of glandular structures are evidence for exclusion of the diagnosis of metastatic adenocarcinoma. Trabecular carcinoma and Merkel cell carcinoma also show findings comparable with EPC. Hyperchromatic, large, and irregular nuclei arranged in cord or trabecular patterns are common features of EPC and trabecular carcinoma; however, the latter shows nuclear molding. On immunoperoxidase studies, EMA and CK-7 are positive, and S-100 protein and CK-20 are negative in EPC. CEA is negative in most EPC; however, it can be positive in tumors containing well-formed ducts2
. However, trabecular carcinoma or Merkel cell carcinomas express neuron-specific enolase (NSE) and CK-20, and they do not express CK-719
. This present case showed positivity for EMA and CK-7 and negativity for S-100 protein, CK-20, and CEA. The negative result for CEA might be due to the paucity of ductal structures in this case.
Snow and Reizner20
suggested local recurrence and regional metastatic rates of approximately 20% and development of distant metastases in 12% of cases. Similarly, Robson et al.2
observed that 11% of patients had metastasis to distant organs; these patients have a high mortality rate (64% in the series). They suggested that the prognosis of EPC depends mainly on mitoses (more than 14 per high power field), lympho-vascular invasion, and a tumor depth of more than 7 mm. The present case was positive for all of these poor prognostic factors, and this might have induced the fatal linical course.
We experienced a rather novel case of EPC on an uncommon site and the patient presented with rapid multiple metastases. Most EPCs are localized and a few of them are metastatic. Therefore, it is essential to consider the possibility of metastases of primary EPC in the process of diagnostic evaluation of patients who are found to be normal on a physical examination.