Choriocarcinoma is a malignant tumor arising from trophoblastic cells and characterized by the secretion of human chorionic gonadotropin (hCG). The lung and the vagina are the common target organs of choriocarcinoma metastasis; however, in some rare cases, metastasis to the liver, brain, kidney, or gastrointestinal tract is also reported12. Skin metastasis is especially known to be extremely rare3. To the best of our knowledge, only 12 cases of cutaneous metastasis of choriocarcinoma have been reported in the literature.

A 30-year-old female patient visited our hospital for the evaluation of a solitary cutaneous nodule on the scalp that had been present for 3 weeks. The lesion was a reddish, bean-sized firm nodule (Fig. 1). There were no subjective symptoms, and no significant findings on physical examination. She had undergone suction and curettage 33 months ago for a hydatidiform mole. A skin punch biopsy was performed. Histologic examination revealed typical histologic features of choriocarcinoma. Marked red blood cell extravasation and dermal infiltration of anaplastic malignant tumor cells were observed. Infiltrated tumor cells consisted of two cell types: (i) cytotrophoblastic cells that had a polygonal clear cytoplasm and large vesicular nuclei with prominent nucleoli, and (ii) syncytiotrophoblastic cells with hyperchromatic nuclei and an eosinophilic cytoplasm (Fig. 2). Moreover, immunohistochemical staining of the cytoplasm of syncytiotrophoblasts against hCG antigen showed a strong positive reaction, leading to the final diagnosis of metastatic choriocarcinoma (Fig. 2, inset). Other germ cell tumors such as polyembryoma, embryonal carcinoma, dysgerminoma, and mixed germ cell tumor can also contain syncytiotrophoblastic cells that will stain positive for hCG; however, in these cases, there are no dysplasias of cytotrophoblasts and syncytiotrophoblasts that will distinguish these diseases from choriocarcinoma4. She was referred to the gynecology department, and the laboratory tests showed an increased serum hCG (275,673 mIU/ml). In the ovary, no specific abnormal findings were observed with ultrasonography. However, multiple nodules that could be considered metastatic were seen on the chest radiograph. She was transferred to another hospital for chemotherapy. The primary site remained unknown, as there had been no further evaluations in this hospital.

Cutaneous metastasis of visceral malignancy is often reported (generally 1.4%~10.4% of the cases)2. However, cutaneous metastasis of choriocarcinoma is rare. According to Gleizal et al.5, the mean patient age in 11 cases of cutaneous metastasis of choriocarcinoma that had been reported until 2007 was 32 years (range, 22~74 years), and the clinical feature of a single reddish nodule similar to that of our patient was observed in 7 cases; however, the manifestation of the disease on the scalp was seen in only 1 other case.

The diagnosis of the disease would be difficult with only physical examinations if the primary presentation of visceral malignancy is cutaneous metastasis; however, the diagnosis was easier in this case because the typical histological findings of choriocarcinoma were observed.

This case emphasizes the importance of the histological examination of a skin metastatic lesion in making a conclusive diagnosis. Here, we report a case of scalp metastasis of choriocarcinoma.