Exploring the role of BAFF as biomarker in the detection of uveal melanoma metastases

Abstract

Purpose: While B-cell activating factor (BAFF) was identified to promote the invasion in other malignancies, its role in the progression of uveal melanoma (UM) still remains unexplored. Here, we analysed the serum level of BAFF in UM patients with regard to its significance as biomarker for the metastases.

Methods: In this retrospective study, serum BAFF levels in 173 UM patients (36 with metastases and 137 without), and 23 healthy controls were measured with a multiplexed sandwich ELISA system and then correlated with clinicopathological characteristics such as primary tumor size, tumor location, histological cell type, sex, cancer stage, cytogenetic alterations of chromosome 3, and the metastatic burden. Immunohistochemical staining of 50 UM tissue specimens was also performed to evaluate the expression of BAFF and its receptors BAFF-R and TACI.

Results: The metastatic patients were identified to have significantly higher serum BAFF levels (mean ± SD, 1520.8 ± 1182.1 pg/ml) than those without metastases (950.4 ± 494.6 pg/ml) and controls (810.3 ± 140.5 pg/ml). While no distinctions were detected with regard to tumor location, histological cell type, gender, and monosomy 3, the patients in cancer stages II, III, and IV displayed higher serum BAFF levels than those in stage I. The serum BAFF level was significantly correlated with the metastatic burden. The serum BAFF level of 1120 pg/ml was identified to have the best performance for distinguishing the metastatic patients from non-metastatic patients. In the kinetic study, we noticed that 20.8% of the analysed patients already demonstrated elevated serum BAFF concentrations before the clinical diagnosis of metastases. Positive BAFF staining was detected in the cytoplasm of single tumor cells (in 13 specimens), macrophages (in 12 specimens), and tumor-infiltrating lymphocytes (TILs) (in 13 specimens). The expressions of BAFF-R and TACI were also observed in 17 and 36 of the 50 tested UM specimens, respectively.

Conclusions: Our study first suggests that BAFF might be a promising serum marker for the detection of UM metastases.

Keywords: B-cell activating factor; Metastasis; Serum markers; Tumor microenvironment; Tumor-infiltrating immune cells; Uveal melanoma.

Fig. 1

a, b The comparison of mean LBD and apical heights between patients with and without metastases showing that the former group had significantly higher LBD and apical height than the latter group. ***P < 0.01

Fig. 2

Scatter plot showing the distribution of serum BAFF levels with mean (red point) and standard deviation (red lines) in control individuals, and patients without and those with metastases. A one-way ANOVA and Tamhane post hoc analysis conducted on the ln^{(serum BAFF)} demonstrated that the patients with metastases had significantly higher concentrations than those without metastases and healthy controls. ***P < 0.01

Fig. 3

a–f The comparison of serum BAFF levels in different tumor locations, histopathological cell types, gender, cancer stages, cytogenetic alterations of chromosome 3, and TILs’ categories. One-way ANOVA and Tamhane post hoc analyses were conducted on the ln^{(serum BAFF)} in the context of different tumor locations, tumor cell types and TILs’ categories, while Student’s t test was conducted to compare the differences between male and female, cancer stage I, and stages II, III, and IV, as well as disomy 3 and monosomy 3. **P < 0.05

Fig. 4

a–c Scatter plots and regressions lines demonstrating the Pearson’s correlations between serum BAFF levels and the LBD (P > 0.05, r = 0.103), apical height of primary tumor (P > 0.05, r = 0.071), and metastatic burden (P < 0.01, r = 0.606), respectively

Fig. 5

Receiver-operating characteristic curve (ROC) analysis of serum BAFF levels in 173 UM patients demonstrating an area under the curve (AUC) of 0.678 with a P value less than 0.01. The x- and y-axis represented 1-specificity and sensitivity, respectively

Fig. 6

a Photomicrographs showing immunohistochemical staining of BAFF in the cytoplasm of UM tumor cells (upper dotted box) and macrophages (lower dotted box), respectively; b photomicrographs showing immunohistochemical staining of BAFF in the cytoplasm of lymphocytes; c–e the comparison of serum BAFF levels in the context of BAFF staining in the tumor cells, macrophages, and TILs, respectively

Fig. 7

a, b Photomicrographs showing immunohistochemical staining of BAFF-R in the cytoplasm and nucleus of UM tumor cells, respectively. The tumor cells containing the positive nuclear staining of BAFF-R were majorly located in the marginal area of the tumor (black arrow in b); c photomicrographs showing immunohistochemical staining of TACI in the cytoplasm of UM tumor cells; d Heatmap showing the clinicopathological features (metastatic status, histological cell types, categories of TILs, and the IHC staining results of BAFF, BAFF-R, TACI, CD3, CD4, CD8, and CD20) of 50 UM specimens