BackgroundTumor hypoxia is relevant for tumor growth, metabolism, resistance to chemotherapy andmetastasis. We have previously shown that hyperoxia, using hyperbaric oxygen treatment(HBOT), attenuates tumor growth and shifts the phenotype from mesenchymal to epithelial(MET) in the DMBA-induced mammary tumor model. This study describes the effect ofHBOT on tumor growth, angiogenesis, chemotherapy efficacy and metastasis in a triplenegative MDA-MB-231 breast cancer model, and evaluates tumor growth using a triple posi tive BT-474 breast cancer model.Materials and methods5 x 105 cancer cells were injected s.c. in the groin area of NOD/SCID female mice. The BT 474 group was supplied with Progesterone and Estradiol pellets 2-days prior to tumor cellinjection. Mice were divided into controls (1 bar, pO2 = 0.2 bar) or HBOT (2.5 bar, pO2 = 2.5bar, 90 min, every third day until termination of the experiments). Treatment effects weredetermined by assessment of tumor growth, proliferation (Ki67-staining), angiogenesis(CD31-staining), metastasis (immunostaining), EMT markers (western blot), stromal com ponents collagen type I, Itgb1 and FSP1 (immunostaining) and chemotherapeutic efficacy(5FU).ResultsHBOT significantly suppressed tumor growth in both the triple positive and negative tumors,and both MDA-MB-231 and BT-474 showed a decrease in proliferation after HBOT. No dif ferences were found in angiogenesis or 5FU efficacy between HBOT and controls. Never theless, HBOT significantly reduced both numbers and total area of the metastastaticlesions, as well as reduced expression of N-cadherin, Axl and collagen type I measured inthe MDA-MB-231 model. No change in stromal Itgb1 and FSP1 was found in either tumormodel.PLOS ONE | https://doi.org/10.1371/journal.pone.0183254 August 23, 2017 1 / 19a1111111111a1111111111a1111111111a1111111111a1111111111OPEN ACCESSCitation: Yttersian Sletta K, Tveitarås MK, Lu N,Engelsen AST, Reed RK, Garmann-Johnsen A, etal. (2017) Oxygen-dependent regulation of tumorgrowth and metastasis in human breast cancerxenografts. PLoS ONE 12(8): e0183254. https://doi.org/10.1371/journal.pone.0183254Editor: Aamir Ahmad, University of South AlabamaMitchell Cancer Institute, UNITED STATESReceived: March 7, 2017Accepted: August 1, 2017Published: August 23, 2017Copyright: © 2017 Yttersian Sletta et al. This is anopen access article distributed under the terms ofthe Creative Commons Attribution License, whichpermits unrestricted use, distribution, andreproduction in any medium, provided the originalauthor and source are credited.Data Availability Statement: All relevant data arewithin the paper and its Supporting Informationfiles.Funding: This work was partly supported by theResearch Council of Norway through its Centre ofExcellence funding scheme, project number223250. The study was also supported by theNorwegian Cancer Society, Helse Vest RHF.Competing interests: The authors have declaredthat no competing interests exist.ConclusionDespite the fact that behavior and prognosis of the triple positive and negative subtypes ofcancer are different, the HBOT had a similar suppressive effect on tumor growth, indicatingthat they share a common oxygen dependent anti-tumor mechanism. Furthermore, HBOTsignificantly reduced the number and area of metastatic lesions in the triple negative modelas well as a significant reduction in the EMT markers N-cadherin, Axl and density of collagentype I.