Merkel cell carcinoma (MCC) is a rare and highly aggressive neuroendocrine malignancy typically involving the skin. The majority of MCC involves the head/neck region and the extremities. Despite the aggressive nature of the disease, there have been several case studies that report spontaneous regression. We report a unique case of spontaneous regression of an MCC in a peculiar region in the anterior mediastinum with no cutaneous involvement.

A 50-year-old man who presented with a mobile low anterior neck mass, proven by biopsy, to be MCC. Subsequent PET/CT confirmed an FDG (Flurodeoxyglucose)-avid upper mediastinal mass. The mass gradually regressed over the course of 1 month subsequent to biopsy and was no longer palpable on exam or visible on subsequent CT scans. The patient was treated with intensity modulated radiation therapy with a total dose of 6,160 cGy in 28 fractions to the site of previously visible primary disease. At-risk nodal basins were also treated. On subsequent follow-up, the patient continued to have no clinical or radiographic signs of disease.

Spontaneous regression of an MCC is rare but has been reported mostly in the head/neck region following biopsy. It is unknown why spontaneous regression occurs. There is a possibility that biopsy may stimulate T-lymphocytes resulting in spontaneous regression.

This is the first case to our knowledge of spontaneous regression of an MCC in the anterior mediastinum with no cutaneous involvement. Most MCC are seen clinically due to skin changes with a majority of cases occurring in the head/neck region.

Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine tumour. Although surgical resection is a treatment choice, it often occurs in the head and neck and occurs mainly in the elderly, making surgery impossible. Radical radiation therapy may be an alternative to surgery in these patients. In addition, radiation treatment may be performed even after recurrence after surgery.

An 82-year-old MCC patient had cT2N0M0, stage IIA MCC on the left cheek that metastasised to lymph node 2 months after surgery. She was treated with radiation monotherapy with a hypofractionation schedule (39 Gy at 3 Gy per fraction).

The patient achieved complete remission after radiotherapy without severe toxicities.

Merkel cell carcinoma is a rare, aggressive neurocutaneous malignancy. This study investigated whether patients with Merkel cell carcinoma in the head and neck had poorer outcomes than patients with Merkel cell carcinoma located elsewhere.

A retrospective study was performed of patients with Merkel cell carcinoma treated at the Jewish General Hospital in Montréal, Canada, from 1993 to 2013. Associations between clinicopathological characteristics and disease-free and disease-specific survival rates were examined according to the Kaplan–Meier method.

Twenty-seven patients were identified. Although basic clinicopathological characteristics and treatments were similar between head and neck and non-head and neck Merkel cell carcinoma groups, disease-free and disease-specific survival rates were significantly lower in the head and neck Merkel cell carcinoma group (log-rank test; p = 0.043 and p = 0.001, respectively). Mortality was mainly due to distant metastasis.

Patients with head and neck Merkel cell carcinoma had poorer survival rates than patients with non-head and neck Merkel cell carcinoma in our study. The tendency to obtain close margins, a less predictable metastatic pattern, and/or intrinsic tumour factors related to the head and neck may explain this discrepancy.