Merkel cell carcinoma with lymph node metastasis in the absence of a primary site: Case report and literature review.

Merkel cell carcinoma (MCC) is a rare malignant skin neoplasm with the potential for local recurrence, spreading to regional lymph nodes (LNs) and distant metastases. Although it has been identified in various anatomical sites, LN metastatic MCC in the absence of a primary site is extremely rare. The present case reports a 54-year-old male who initially underwent histological examination of a biopsy specimen from the right inguinal LNs. A diagnosis of metastatic small cell carcinoma was made. Nine months later, this diagnosis was changed to MCC with multiple metastases following observation of a tumour mass in the right dorsal thigh. Additionally, in the present study a summary is provided of 23 published cases of MCC with initial LN metastasis in the absence of a primary site, with details of clinical characteristics, natural history and pertinent therapy of this uncommon tumour. The present patient with LN metastatic MCC in the absence of a primary site and the other reported cases demonstrate that although multimodal treatment with surgery, radiotherapy (RT) and chemotherapy provides excellent local control, local recurrence and distant metastases commonly develop in this uncommon tumour. LN metastatic MCC in the absence of a primary site is a highly malignant disease and the role of adjuvant postoperative RT and/or chemotherapy remains to be fully determined.