Association of increased osteopontin and splice variant-c mRNA expression with HER2 and triple-negative/basal-like breast carcinomas subtypes and recurrence

Summary Osteopontin, a secreted phosphoglycoprotein, promotes tumor progression through binding to integrins and CD44 cell receptors. Its overexpression has been correlated with metastasis and adverse outcome in several neoplasms. In breast carcinoma, osteopontin mRNA and its splicing variant-c, a suggested marker for transformed cells, have not been extensively analyzed. Immunohistochemistry was performed in 415 breast carcinomas to examine total osteopontin and osteopontin-c protein distribution. RNA was extracted and retrotranscribed to cDNA from 309 tumors classified into immunophenotypes and in six cell lines representing the breast cancer subtypes. Total osteopontin and osteopontin-c mRNA levels were measured by quantitative RT-polymerase chain reaction. The median fold change of total osteopontin mRNA was higher in HER2-positive (fold-change = 14.7) and triple-negative/basal-like (fold-change = 14.7) tumors, whereas osteopontin-c mRNA was elevated in triple-negative/basal-like subtype (fold-change = 2.8). Total osteopontin levels were increased in SK-BR-3 (HER2-positive) and MDA-MB-468 (triple-negative/basal-like) cell lines. Higher total and osteopontin-c mRNA levels were seen in tumors of high grade, with necrosis, positive nodal status and high Nothingam Prognostic Index score. Disease-free survival was significantly shorter for patients whose tumors overexpressed total osteopontin (67% vs 73%). Moreover, increased osteopontin-c stratified subgroups of patients at higher risk of recurrence among immunophenotypes, especially in triple-negative/basal-like subtype (70% vs 83%). By multivariate analyses for disease-free survival, osteopontin-c emerged as a significant predictor of relapse. In summary, our data showed an association of osteopontin with poor prognostic factors, aggressive subtypes HER2 and triple-negative/basal-like, and higher risk of recurrence.