Clinical significances of <i>RPL15</i> gene expression in circulating tumor cells of patients with breast cancer

The preferred biomarkers for evaluating the outcomes of patients with breast cancer (BC) remain poorly understood. The present study aimed to investigate the predictive roles of circulating tumor cells (CTCs) and ribosomal protein L 15 (<i>RPL15)</i> expression in the prognosis of patients with BC. A total of 170 patients were included in the present study, all of whom were female. BC was diagnosed by combining clinical features, imaging and pathological findings. CanPatrol^™ technology and triple color <i>in situ</i> RNA hybridization were used to detect CTC subtypes and <i>RPL15</i> gene expression levels. CTCs were classified into epithelial CTCs, mesenchymal CTCs (MCTCs), and hybrid CTCs (HCTCs) according to cellular surface markers. Risk factors for recurrence and metastasis were validated by a multivariate COX regression model. Kaplan-Meier survival curves were used to determine the progression-free survival (PFS) of patients. The results showed that patients with advanced tumor-node-metastasis stage and triple negative BC had high MCTCs, HCTCs and <i>RPL15</i> levels (P<0.05). Furthermore, the multivariate COX regression analysis revealed that MCTCs, HCTCs, HER2⁺ and positive <i>RPL15</i> gene expression were key factors for recurrence and metastasis of patients (P<0.05). The PFS of patients with >2 MCTCs/5 ml blood, >5 HCTCs/5 ml blood, and positive <i>RPL15</i> gene expression in CTCs were significantly shorter than that of patient with 2 MCTCs, 5 HCTCs, and negative <i>RPL15</i> gene expression in CTCs (P<0.05). By contrast, the PFS of patients with positive HER2 also was significantly shorter than that of patients with negative HER2. Overall, the present data indicated that the PFS of patients with BC with >2 MCTC or >5 HCTCs, and positive <i>RPL15</i> gene expression was shorter than that of those with 2 MCTCs or 5 HCTCs, and negative <i>RPL15</i> gene expression. Additionally, the prognosis of patients with BC with negative HER2 is more favorable than the prognosis of patients with positive HER2 expression.