Track

Abstract

Introduction: There is currently no standardized sentinel lymph node (SLN) immunohistochemistry (IHC) protocol for detecting Merkel cell carcinoma (MCC) metastases. A cost-effective, high-sensitivity IHC panel could improve diagnostic accuracy, patient stratification, and resource utilization.

Methods: We evaluated 207 SLNs from 69 MCC patients using a panel of POU4F3, CK20, keratin AE1/AE3, and pan-keratin. Metastasis was defined as positive staining for any of the tested IHC markers.

Results: Patients ranged from 49-88 years (median: 71), with a male:female ratio of 1.9:1. Primary tumor sites were extremities (48%), head/neck (35%), and trunk (17%). SLN locations included axillary (29%), cervical (26%), inguinal (20%), femoral (13%), facial (9%), epitrochlear (1.4%), and pelvic (1.4%). Metastases were identified in 102/207 (49%) SLNs. Single marker sensitives were: POU4F3 (96%, 98/102), AE1/AE3 or pan-keratin (69%, 70/102), and CK20 (67%, 68/102). The most sensitive combinations were POU4F3 with CK20 or POU4F3 with AE1/AE3 or pan-keratin (both 100% sensitivity, 102/102). CK20 with AE1/AE3 or pan-keratin was least sensitive (74%, 75/102).

Conclusion: POU4F3 is the most sensitive individual IHC marker for detecting MCC SLN metastases. The optimal cost-effective panel is POU4F3 with AE1/AE3 or pan-keratin, which achieves 100% sensitivity while reducing reliance on less effective stains. Adoption of this focused IHC panel may serve to standardize SLN evaluation for MCC and improve diagnostic and staging accuracy and efficiency.