High prognostic potential of a transcriptomic signature related to cycling hypoxia: direct application to breast cancer profiling

Purpose. Temporal and local fluctuations in oxygen levels observed within tumors represent stressful conditions requiring adaptive mechanisms that provide tumor cells with phenotypic alterations to survive and proliferate in this hostile environment. The analysis of the transcriptome associated with such cycling hypoxia could thus represent a prognostic biomarker of cancer progression. Patients and Methods. We exposed 20 cell lines derived from various tissues to repeated periods of hypoxia/reoxygenation in order to determine a transcriptomic signature of cycling hypoxia (CycHyp). We then used clinical data sets from 2,150 patients with primary breast cancer to estimate a prognostic Cox proportional hazard model and to assess the prognostic performance of the CycHyp signature on independent samples. Results. The prognostic potential of the CycHyp signature was validated in patients independently of the receptor status of the tumors (HR=1.97; p = 1.8e-12). The discriminating capacity of the CycHyp signature was further increased in the ER+ HER2- patient populations (HR = 2.34, p = 9e-12) including those with a node negative status receiving or not a treatment (HR = 3.32 and 5.51; p= 5.61e-10 and 8.15e-11, respectively). We also documented the capacity of the CycHyp signature to outperform existing prognostic gene signatures with significantly higher BCR and concordance index. We also showed that the CycHyp signature could identify ER-positive node-negative breast cancer patients at high risk based on conventional clinico-pathologic criteria but who could have been spared from chemotherapy and inversely those patients classified at low risk based on the same criteria but who presented a negative outcome. Conclusion. This study demonstrates that a gene signature derived from the transcriptomic adaptation of tumor cells to cycling hypoxia is prognostic of breast cancer and offers a unique decision making tool to complement the discrimination of breast cancer patients based on anatomo-pathological evaluation. The prognostic value of CycHyp further confirms the link between cycling hypoxia and cancer progression, and thereby paves the way for a broad applicability to evaluate cancer patient outcomes. Twenty cancer cell lines were exposed to 3 different culture conditions: normoxia (21% O2), continuous hypoxia (1% O2), and cycling hypoxia (24 cycles of 30min normoxia+30 min hypoxia). Gene signatures were generated based on gene expression differences between Normoxia and continuous hypoxia or cycling hypoxia.