Microarray immunohistochemistry showed that breast cancer tissue had high Siglec-15 protein expression
The expression level and positive rates of Siglec-15 were compared between breast cancer tissue and adjacent normal tissue samples by immunohistochemistry on a microarray. The samples in odd columns are from breast cancer tissues (Fig. 1A, E). The samples in even columns are from adjacent normal tissues (Fig. 1A, E). Figure 1B, C and D shows a classic pair of samples. Breast cancer tissue had higher positive staining (Fig. 1C) than adjacent tissue (Fig. 1D). Breast cancer tissues had a higher Siglec-15-positive staining rate (70.79 ± 6.95%) than adjacent normal tissues (46.78 ± 7.05%, p < 0.001, Fig. 1F).
Databases Showed That Breast Cancer Tissue Had High Siglec-15 Mrna Expression
From the Cancer Genome Atlas database, we obtained 1,091 breast cancer samples and 113 control samples. In the breast cancer samples, 844 cases contained both clinical and Siglec-15 gene expression data. The detailed clinical characteristics are listed in Table 1.
Clinical Characters
|
Case, N
|
%
|
Table 1
Clinical characteristics of breast cancer patients who had Siglec-15 and tumor-infiltrating immune cells data
Tumor size
|
T1
|
215
|
25.47
|
(TNM-T)
|
T2
|
493
|
58.41
|
|
T2
|
106
|
12.56
|
|
T4
|
28
|
3.32
|
|
NA
|
2
|
0.24
|
(TNM-N)
|
N0
|
395
|
46.80
|
|
N1
|
297
|
35.19
|
|
N2
|
98
|
11.61
|
|
N3
|
64
|
7.58
|
|
NA
|
11
|
1.30
|
(TNM-M)
|
M0
|
709
|
84.00
|
|
M1
|
16
|
1.90
|
|
NA
|
119
|
14.10
|
Stage
|
I
|
137
|
16.23
|
|
II
|
475
|
56.28
|
|
III
|
199
|
23.58
|
|
IV
|
15
|
1.78
|
|
NA
|
16
|
1.90
|
Total
|
|
844
|
100.00
|
NA: not available; Siglec-15: Sialic acid binding Ig-like lectin 15 |
We compared Siglec-15 expression in breast cancer and normal tissues. The results indicated that Siglec-15 expression was higher in breast cancer tissues than in normal controls (Fig. 2A, 2.10 vs. 1.34. p = 0.000326).
TNM-T1 had higher expression of Siglec-15 than the control groups (Fig. 2B, p = 0.002). However, no significant difference was found between them (Normal vs. T2: p = 0.262, Normal vs. T3: p = 0.150, Normal vs. T4: p = 0.289, Table 2). Moreover, TNM-N0 and N1 had higher expression of Siglec-15 than the control groups (Fig. 2C). TNM-M0 had higher expression of Siglec-15 than the control groups (p = 0.062, Fig. 2D). Furthermore, stage I had higher expression of Siglec-15 than the control groups (p = 0.005, Fig. 2E). However, the expression of Siglec-15 did not differ among other TNM-Ns, TNM-Ms and stages (Table 2).
Tnbc Patients With High Siglec-15 Expression Had Poorer Survival
Kaplan–Meier survival analysis suggested that triple-negative breast cancer patients with high Siglec-15 expression had a poorer prognosis than those with low Siglec-15 expression (p = 0.042, Fig. 3A). However, an interesting finding is that low Siglec-15 expression had a poorer prognosis in luminal A subtypes (p = 0.029, Fig. 3B). Siglec-15 expression did not influence survival in the luminal B (p = 0.51, Fig. 3C) and HER2+ (p = 0.71, Fig. 3D) subtypes. The Kaplan–Meier Plotter database (https://kmplot.com) was used to validate the survival analysis and calculate the hazard ratio. The findings confirmed that triple-negative breast cancer patients with high Siglec-15 expression had a poorer prognosis than those with low Siglec-15 expression (HR = 1.59, 95% confidence interval 1.11–2.29. p = 0.011, Supplementary Fig. 3).
Composition Of Tumour-infiltrating Immune Cells
We performed CIBERSORT to investigate the fractions of infiltrated immune cells between high Siglec-15 breast tumour tissue, low Siglec-15 breast tumour tissue and adjacent nontumour tissues. A bar plot was drawn to visualize the proportions of infiltrating immune cells (Fig. 4A).
The breast cancer tissues with high Siglec-15 expression had low fractions of activated dendritic cells (p < 0.001), follicular helper T cells (p < 0.001), activated memory CD4 T cells (p < 0.001) and M1 macrophages (p = 0.008, Fig. 4B, C).
The breast cancer tissues with high Siglec-15 expression had high fractions of resting memory CD4 T cells (p < 0.001), resting dendritic cells (p < 0.001), and resting mast cells (p < 0.001, Fig. 4B, C).