The Prognostic Role of CD68 and FoxP3 Expression in Primary Central Nervous System Lymphoma

Background

The prognostic role of CD68⁺ tumor-associated macrophages (TAMs) and tumor infiltrating T-cells including FoxP3⁺ regulatory T-cells (Tregs) has been extensively evaluated in areas of lymphoma research, however their expression and prognostic role have little been explored in primary central nervous system lymphoma (PCNSL). Therefore, we investigated CD68 and FoxP3 expression in tumor microenvironment of PCNSL and evaluated its prognostic role.

Methods

Seventy-six consecutive immunocompetent patients diagnosed with PCNSL between December 2004 and April 2015 treated homogenously with high-dose methotrexate (HD-MTX)-based chemotherapy as an initial treatment in Severance Hospital, Seoul, S. Korea and for whom archived formalin-fixed and paraffin-embedded (FFPE) tissue blocks for initial diagnosis were available were retrospectively identified. We studied CD68 and FoxP3 expression by immunohistochemical staining on FFPE biopsy specimen and evaluated correlations of their expression with obtained clinical data, treatment response depending on the upfront ASCT, and survival of the patients. The cut-off value for the expression of CD68⁺ TAMs and FoxP3⁺ Tregs were evaluated by the area under curve (AUC) of the receiver operating characteristic (ROC) curve for analysis purposes, and we established cut-offs of 55 cells/high power field (HPF) for CD68 and 15 cells/HPF for FoxP3. We stratified patients based on CD68 and FoxP3 expression according to the cut-off values we determined from the AUC. The overall survival (OS) and progression-free survival (PFS) were plotted using the Kaplan-Meier method and compared using the log-rank test. The Cox proportional-hazards regression model was used in both univariate and multivariate analyses.

Results

The median age of the patients was 57 (range 33-79) years. The median follow-up duration for survivors was 23.2 months (range, 2.4-128.5). Sixteen (21.1%) patients underwent upfront ASCT, after median 4 (range 2-4) cycles of HD-MTX based chemotherapy. The 2-year OS and PFS rates for all patients were 75.2% and 43.3%, respectively. The patients did not reach median OS, and the median PFS was 17.9 months (95% confidence interval [CI], 9.4-26.4). The median level of expression for CD68⁺ TAM/HPF was 25 (range, 5-80) and the median level of expression for FoxP3⁺ Tregs/HPF was 0 (range, 0-68). The difference in OS and PFS between the high and low CD68 groups was significant in the univariate (hazard ratio [HR] = 2.79, 95% CI: 0.97-8.03, P = 0.058 for OS, and HR = 2.17, 95% CI: 1.03-4.58, P = 0.043 for PFS), as well as in the multivariate analysis (HR = 3.71, 95% CI: 1.25-11.02, P = 0.018 for OS, and HR = 4.83, 95% CI: 1.91-12.27, P = 0.001 for PFS). The patients with high CD68 expression exhibited 2-year OS and PFS rates of 42.9%, and 10.0%, respectively, in comparison to 81.5%, and 50.7% for those with low CD68 expression (P = 0.048 for OS, and P = 0.035 for PFS) (Figure 1A, 1B). In a subgroup analysis of 60 patients who did not receive upfront ASCT, high CD68 expression was associated with inferior OS and PFS compared to low CD68 expression (P = 0.014 for OS, and P = 0.016 for PFS) (Figure 1C, 1D). The difference in OS and PFS between the high and low CD68 expression groups in the non-upfront ASCT subgroup (n = 60) was significant in the univariate (HR = 3.63, 95% CI: 1.21-10.88, P = 0.021 for OS, and HR = 2.60, 95% CI: 1.15-5.86, P = 0.021 for PFS) as well as in the multivariate analysis (HR = 4.05, 95% CI: 1.35-12.16, P = 0.013 for OS, and HR = 5.80, 95% CI: 2.25-14.95, P < 0.001 for PFS). However, the OS and PFS in the upfront ASCT cohort (n = 16) were similar between the high and low CD68 expression groups (P = 0.426 and P = 0.848, respectively) (Figure 1E, 1F). There were no differences in OS and PFS according to the expression level of FoxP3 in all patients as well as in subgroup of patients who did not receive upfront ASCT.

Conclusion

High level of CD68 expression in patients with PCNSL was significantly associated with inferior OS and PFS, especially in non-upfront ASCT treated subgroup of patients. FoxP3 expression level was also not associated with survival in this study. We suggest CD68 as a potential biomarker at initial PCNSL diagnosis and upfront ASCT consolidative strategy might improve survival in PCNSL patients by overcoming negative impact of high CD68 expression. Further validation studies are warranted.

Figure 1.

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Figure 1.

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