Loss of circadian clock gene expression is associated with tumor progression in breast cancer

Dec 9, 2014Cell cycle (Georgetown, Tex.)

Reduced daily rhythm gene activity is linked to breast cancer growth

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Abstract

Higher expression of several clock genes is associated with longer metastasis-free survival in breast cancer patients.

Expression of 17 clock components was examined in tumors from 766 untreated, node-negative breast cancer patients.
Univariate analyses indicated that higher levels of CLOCK, PER1, PER2, PER3, CRY2, NPAS2, and RORC correlate with improved metastasis-free survival.
In the ER+/HER2- subtype, PER1, PER3, CRY2, and NFIL3 showed prognostic relevance, while CLOCK and NPAS2 were significant in the ER-/HER2- subtype.
Multivariate analysis identified PER3 and RORC as independent prognostic factors for survival, with hazard ratios of 0.66 and 0.42, respectively.
Stronger correlations between certain clock genes were observed in less aggressive tumors, while weaker correlations were noted in more aggressive forms.

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Several studies suggest a link between circadian rhythm disturbances and tumorigenesis. However, the association between circadian clock genes and prognosis in breast cancer has not been systematically studied. Therefore, we examined the expression of 17 clock components in tumors from 766 node-negative breast cancer patients that were untreated in both neoadjuvant and adjuvant settings. In addition, their association with metastasis-free survival (MFS) and correlation to clinicopathological parameters were investigated. Aiming to estimate functionality of the clockwork, we studied clock gene expression relationships by correlation analysis. Higher expression of several clock genes (e.g., CLOCK, PER1, PER2, PER3, CRY2, NPAS2 and RORC) was found to be associated with longer MFS in univariate Cox regression analyses (HR<1 and FDR-adjusted P < 0.05). Stratification according to molecular subtype revealed prognostic relevance for PER1, PER3, CRY2 and NFIL3 in the ER+/HER2- subgroup, CLOCK and NPAS2 in the ER-/HER2- subtype, and ARNTL2 in HER2+ breast cancer. In the multivariate Cox model, only PER3 (HR = 0.66; P = 0.016) and RORC (HR = 0.42; P = 0.003) were found to be associated with survival outcome independent of established clinicopathological parameters. Pairwise correlations between functionally-related clock genes (e.g., PER2-PER3 and CRY2-PER3) were stronger in ER+, HER2- and low-grade carcinomas; whereas, weaker correlation coefficients were observed in ER- and HER2+ tumors, high-grade tumors and tumors that progressed to metastatic disease. In conclusion, loss of clock genes is associated with worse prognosis in breast cancer. Coordinated co-expression of clock genes, indicative of a functional circadian clock, is maintained in ER+, HER2-, low grade and non-metastasizing tumors but is compromised in more aggressive carcinomas.

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Loss of circadian clock gene expression is associated with tumor progression in breast cancer

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