Clinical benefit of baseline imaging in Merkel cell carcinoma: Analysis of 584 patients.

Abstract

Merkel cell carcinoma (MCC) guidelines derive from melanoma and do not recommend baseline cross-sectional imaging for most patients. However, MCC is more likely to have metastasized at diagnosis than melanoma. To determine how often baseline imaging identifies clinically occult MCC in patients with newly diagnosed disease with and without palpable nodal involvement. Analysis of 584 patients with MCC with a cutaneous primary tumor, baseline imaging, no evident distant metastases, and sufficient staging data. Among 492 patients with clinically uninvolved regional nodes, 13.2% had disease upstaged by imaging (8.9% in regional nodes, 4.3% in distant sites). Among 92 patients with clinically involved regional nodes, 10.8% had disease upstaged to distant metastatic disease. Large (>4 cm) and small (<1 cm) primary tumors were both frequently upstaged (29.4% and 7.8%, respectively). Patients who underwent positron emission tomography-computed tomography more often had disease upstaged (16.8% of 352), than those with computed tomography alone (6.9% of 231; P = .0006). This was a retrospective study. In patients with clinically node-negative disease, baseline imaging showed occult metastatic MCC at a higher rate than reported for melanoma (13.2% vs <1%). Although imaging is already recommended for patients with clinically node-positive MCC, these data suggest that baseline imaging is also indicated for patients with clinically node-negative MCC because upstaging is frequent and markedly alters management and prognosis.