Evaluation of the association of CXCR4 expression with HER2 status or mTOR expression levels

Abstract

e22192 Introduction: CXCR4 is a chemokine receptor that is linked to breast cancer metastasis. The putative mechanism involves activation of the HER-2/PI3K/PTEN/Akt/mammalian target of rapamycin (mTOR) pathway, resulting in enhanced synthesis of downstream proteins such as CXCR4 and eukaryotic initiation factor 4E (eIF4E). Overexpression of eIF4E has been shown to be an independent predictor of breast cancer outcome. Because HER-2/mTOR/CXCR4 pathway has mainly been observed in vitro, it deserves scrutiny to determine whether it is also seen in human breast cancers. We hypothesize that HER-2/mTOR axis is not significantly associated with CXCR4 regulation in human breast cancers. Method: 107 stages 1 - 3 breast cancers from a prospective breast cancer database were analyzed. Samples were quantified for mTOR, CXCR4, and eIF4E levels by Western Blot. mTOR, and eIF4E levels were quantified as fold-over benign breast tissues and CXCR4 levels were quantified as fold-over Hela cells. CXCR4 overexpression was defined as low (< 6.0 fold) or high (≥ 6.0 fold), and eIF4E expression level was separated into tertiles. Primary end points were cancer recurrence and death. Statistical analyses performed were independent student t-test, Spearman correlation, Kaplan-Meier survival curves, log-rank test, and Cox proportional hazard model. Results: All 59 HER-2 (-) and 48 HER-2 (+) breast cancer specimens overexpressed CXCR4 (mean=6.18 ±4.4), mTOR (mean=1.24 ±1.58), and eIF4E (mean=9.53 ±6.42). Unlike in vitro data, there was no difference in mean CXCR4 expression level between HER-2 (-) and HER-2 (+) tumors (mean=6.55, 5.72, respectively) (p=0.33). While mTOR correlated significantly with eIF4E level (p=0.0006, r = 0.34), it did not correlate with CXCR4 level (p=0.713, r=0.036). Only nodal status (p=0.04) and eIF4E level (p=0.03) were independent predictors of breast cancer death. Conclusions: We demonstrate that CXCR4 regulation in human breast cancers is more complex than previously thought. There was no correlation between mTOR and CXCR4 levels, nor was there a difference in mean CXCR4 overexpression levels between HER-2 (+) and HER-2 (-) tumors. Pathways regulating CXCR4 expression warrant further investigation. No significant financial relationships to disclose.