# Pericardial Oligometastasis From Merkel Cell Carcinoma Treated With Stereotactic Ablative Radiotherapy

## TL;DR

A rare case of pericardial cancer spread from Merkel cell carcinoma was successfully treated with targeted radiation, showing long-term improvement.

## Contribution

This is the longest reported response duration for pericardial oligometastasis from MCC treated with SABR.

## Key findings

- SABR treatment led to a significant reduction in the pericardial nodule size within 2.3 months.
- A clinical complete response was achieved 8.9 months post-treatment.
- The patient showed a durable response with no recurrence at 40.1 months post-SABR.

## Abstract

Merkel cell carcinoma (MCC) is a rare and aggressive neuroendocrine skin cancer that often has a poor prognosis due to its propensity for distant metastases. A 74-year-old man with a history of MCC of the left forearm, previously treated with surgery and adjuvant radiotherapy, was found to have an asymptomatic pericardial nodule associated with pericardial effusion on routine follow-up imaging. Subsequent biopsy confirmed metastatic MCC. Restaging demonstrated no other sites of metastases. The pericardial metastasis was treated with stereotactic ablative radiotherapy (SABR) to a dose of 40 Gray (Gy) in five daily fractions. A significant decrease in the size of the pericardial nodule was observed 2.3 months post-SABR, and a clinical complete response was achieved 8.9 months post-SABR. Apart from an asymptomatic mildly increased pericardial effusion, no other acute or late adverse effects were observed. At 40.1 months post-SABR, the patient continued to show a durable response to treatment with no evidence of recurrence. To the best of our knowledge, this case of pericardial oligometastases from MCC treated with SABR is the longest reported duration of response.