Prognostic Significance of Sentinel Lymph Node Mapping in Merkel Cell Carcinoma: Systematic Review and Meta-Analysis of Prognostic Studies

AIM To assess through a systematic review and meta-analysis of the literature the prognostic implication of sentinel lymph node mapping in Merkel cell carcinoma (MCC). MATERIALS AND METHODS PubMed and SCOPUS databases were searched by using "Merkel AND sentinel" as keywords. All studies with prognostic information regarding SLN mapping in cN0 MCC patients were included. Hazard ratio (HR) for overall survival (OS) and disease free survival (DFS) was used as effect size. RESULTS SLN biopsy predicted better DFS and OS as compared to the nodal observation in cN0 MCC patients (pooled HR for DFS: 1.61 (95% CI: 1.05-2.46), P = 0.028; pooled HR for OS: 1.08 (95% CI: 0.55-2.10), P = 0.8). Pathologically negative SLN (SLN-) patients had better OS (pooled HR: 4.42 (95% CI: 1.82-10.7), P = 0.0009) and DFS (pooled HR: 2.58 (95% CI: 1.78-3.73)) as compared to SLN+ patients. CONCLUSION SLN mapping can provide strong prognostic information regarding OS and DFS in cN0 MCC patients. More importantly, SLN mapping can improve DFS and possibly OS in cN0 MCC patients as compared to nodal observation. As MCC is a rare tumor, large multicenter prospective studies are still needed to validate the survival benefit of SLN mapping.