Can Peptide-Targeted Radiation Therapy Treat Advanced Merkel Cell Skin Cancer? A Review of 37 Patients

Of 37 patients with metastatic Merkel cell carcinoma who received 1-5 cycles of PRRT using 177Lu- or 90Y-labeled somatostatin analogs (cumulative activity 1.5-30 GBq), radiographic response data was available for 19 who received PRRT alone. Six of these 19 patients (31.6%) achieved objective responses ranging from partial to complete. No severe adverse events were reported across the treated cohort.

The authors performed a comprehensive literature review searching for all published reports of PRRT use in metastatic Merkel cell carcinoma. They compiled data from individual case reports and small series, totaling 37 treated patients. Response was assessed radiographically in patients who received PRRT as a standalone therapy.

Metastatic Merkel cell carcinoma has limited treatment options and a poor prognosis. While immunotherapy has improved outcomes, many patients don't respond or eventually progress. PRRT offers a mechanistically different approach — using peptides to deliver targeted radiation directly to tumor cells — that could fill an important treatment gap for this rare cancer.

PRRT has already been approved for gastroenteropancreatic neuroendocrine tumors and is being explored for other cancers that express somatostatin receptors. Success in Merkel cell carcinoma would expand the reach of peptide-targeted radionuclide therapy to rare skin cancers. Prospective clinical trials are now underway to generate stronger evidence.

The evidence quality is low — data comes from retrospective case reports and small series rather than controlled trials. The total of 37 patients is very small, and radiographic response data was only available for 19 who received PRRT alone. Publication bias likely favors positive outcomes. Patient selection (requiring somatostatin receptor expression) means results may not apply to all Merkel cell carcinoma cases.