Prognostic significance of CD9 expression differs between tumour cells and stromal immune cells, and depends on the molecular subtype of the invasive breast carcinoma.
OBJECTIVE
CD9, a tetraspanin transmembrane protein, modulates cell motility, migration, and proliferation. The aim of this study was to investigate the prognostic significance of CD9 expression in patients with invasive breast carcinoma (IBC).


RESULTS
CD9 expression was evaluated in tissue microarrays of 1349 IBC samples via immunohistochemistry. CD9 expression in tumour cells (T-CD9 expression) and CD9 expression in stromal immune cells (S-CD9 expression) were analysed separately. T-CD9 expression was observed in 732 (54.3%) cases, and was associated with lymph node metastasis, histological type, lymphovascular invasion, high histological grade, HER2 positivity, a high Ki67 labelling index, and distant metastasis. S-CD9 expression was observed in 833 (61.7%) cases, and was associated with large tumour size, histological type, high histological grade, negative hormone receptors, HER2 positivity, a high Ki67 labelling index, and tumour-infiltrating lymphocytes. Patients with T-CD9 expression had shorter disease-free survival (DFS) than those without T-CD9 expression in the univariate and multivariate analyses. However, S-CD9 expression correlated significantly with a favourable DFS in the univariate and multivariate analyses. In the subgroup analysis, T-CD9 expression and S-CD9 expression were independent markers for DFS in luminal A and luminal B (HER2-negative) subgroups, respectively.


CONCLUSIONS
T-CD9 expression could be a biomarker for poor prognosis in luminal A IBC, whereas S-CD9 expression could be a marker of good prognosis in luminal B (HER2-negative) IBC. Therefore, tumour compartment-specific analyses considering molecular subtypes are necessary to study the prognostic significance of CD9 expression in IBC.
Department of Pathology, Yeungnam University College of Medicine, Daegu, Korea.
Hee Jung
HJ
Kwon
Department of Surgery, Yeungnam University College of Medicine, Daegu, Korea.
Jung Eun
JE
Choi
Department of Surgery, Yeungnam University College of Medicine, Daegu, Korea.
Su Hwan
SH
Kang
Department of Biochemistry and Molecular Biology, Yeungnam University College of Medicine, Daegu, Korea.
Youlim
Y
Son
Department of Pathology, Yeungnam University College of Medicine, Daegu, Korea.
Young Kyung
http://orcid.org/0000-0002-6689-9413
YK
Bae
D000328:Adult; D000368:Aged; D014408:Biomarkers, Tumor / Q000032:analysis*; D001943:Breast Neoplasms / Q000235:genetics / Q000401:mortality / Q000473:pathology*; D018572:Disease-Free Survival; D005260:Female; D006801:Humans; D053208:Kaplan-Meier Estimate; D016246:Lymphocytes, Tumor-Infiltrating / Q000473:pathology; D008875:Middle Aged; D011379:Prognosis; D060245:Tetraspanin 29 / Q000032:analysis*
D014408:Biomarkers, Tumor; C554869:CD9 protein, human; D060245:Tetraspanin 29
CD9; breast neoplasms; immunohistochemistry; prognosis