AbstractPurpose: In a previous immunohistochemical study of dendritic cells (DC) in sentinel lymph nodes (SLN) draining regressing melanomas, we found that the accumulation of mature DC-LAMP+ DCs in SLNs was associated with local expansion of antigen-specific memory effector CTLs and the absence of metastasis in downstream lymph nodes. The aim of this study was to investigate the prognostic importance of the maximal density of mature DCs in SLNs.Experimental Design: A total of 458 consecutive patients with micrometastatic melanoma within SLNs were eligible for analysis. The maximal density of mature DC-LAMP+ DCs was evaluated by three independent observers and categorized into three classes (<100, 100 to <200, and ≥200/mm2).Results: There was excellent interobserver reproducibility for maximum density of mature DC-LAMP+ DC scores (κ score = 0.82). There were differences in the maximal density scores and staining intensity according to the treating melanoma center (P < 0.001). The higher the mature DC density in the SLN is, the longer is the duration of survival [P = 0.047; hazard ratio, 0.70; 95% confidence interval, 0.50-1.00]. Adjusted by thickness and ulceration, the prognostic importance of DC density was lower (P = 0.36).Conclusion: This study is the first to report the prognostic value of DC-LAMP+ DC counts in SLNs containing metastatic melanoma. Patients with a high density of mature DCs (≥200/mm2) have the lowest risk of death. It also provides evidence that a lack of maturation in the SLNs is important in biological facilitation of melanoma progression.