Prognostic impact of B-cell density in cutaneous melanoma

Abstract

Studies on the prognostic importance of tumor-infiltrating lymphocytes have mainly focused on T cells, while little is known about the role of tumor-infiltrating B lymphocytes. We investigated the prevalence of CD20(+) B cells by immunohistochemistry in primary melanoma samples of 106 patients and analyzed in relation to clinicopathological parameters and patients' survival. The majority of samples contained a significant amount of B lymphocytes, predominantly dispersed in the stroma surrounding tumor deposits (mean peritumoral and intratumoral densities: 178.7 ± 156.1 vs. 4.9 ± 6.9 cells/mm², respectively). B cells organized in follicle-like aggregates were also observed in 26% of the samples. B-cell density correlated with that of activated (CD25(+) or OX40(+)) T lymphocytes. Infiltration by CD20(+) lymphocytes did not correlate with tumor thickness, while the presence of B-cell aggregates was observed more frequently in thick melanomas. On the other hand, B-cell infiltration was more pronounced in nonmetastatic or lymph node metastatic tumors, compared to visceral metastatic ones. Accordingly, high number of these cells provided significant survival advantage (P = 0.0391 and P = 0.0136 for intra- and peritumoral infiltration, respectively). Furthermore, combination of peritumoral B-cell density with the number of activated T lymphocytes identified patient subgroups with different disease outcome, which was most favorable in the case of high density, while very poor in the case of low density of both cell types. Multivariate survival analysis identified tumor thickness and CD20(+)/OX40(+) cell density combination as significant independent prognostic factors. Taken together, our results show correlation between low number of CD20(+) B lymphocytes and melanoma progression, indicating a possible role of tumor-infiltrating B cells in antitumoral immune response. It was also reflected in better outcome of the disease since the density of B lymphocytes alone as well as in combination with that of activated T cells proved of prognostic importance in patients with malignant melanoma.

Fig. 1

CD20⁺ B lymphocytes (AEC, red) dispersed in the infiltrate (a) and clustered in dense aggregate (b) in melanoma. Double staining for OX40 or CD25 (developed by Vector SG, gray signal) and CD20 (developed by fuchsin, red signal). CD20⁺ B cells can be seen in close contact with CD25⁺ (c) and OX40⁺ (d) T lymphocytes (arrows). Pictures were taken using ×40 objective

Fig. 2

B-cell density according to metastasis formation. Data are presented as mean and SEM of CD20⁺ cell density

Fig. 3

Kaplan–Meier survival curves for melanoma patients, subdivided according to the intratumoral (a) or peritumoral (b) B-cell density, or to peritumoral densities of CD20⁺ and CD25⁺ (c) or CD20⁺ and OX40⁺ cells (d)