At present, there are few studies on the side effects of chemotherapy in breast cancer patients at high altitude area, and there are no studies on the relationship between oxygen inhalation and fatigue after chemotherapy in breast cancer patients at high altitude. The investigators intend to explore whether oxygen inhalation can improve fatigue at high altitude through this prospective randomized study. In our study, a single center, open-label, randomized phase 2 clinical trial will conduct to investigate whether oxygen inhalation during chemotherapy can improve chemotherapy-related fatigue in patients with breast cancer. The effects of oxygen inhalation on side effects of chemotherapy such as Cancer related fatigue (CRF) were observed. The investigators intend to explore whether oxygen therapy can improve fatigue at high altitude through this prospective randomized study. The investigators enrolled breast cancer patients before chemotherapy. The investigators will use the checklist individual strength(CIS) and the brief fatigue inventory (BFI) to evaluate the fatigue status of patients, and extract the blood of patients for evaluate blood pro-inflammatory cytokines IL-1 β, IL-6, C-reactive protein (CRP), transforming growth factor (TGF-β), soluble tumor necrosis factor (TNF) receptor II (sTNF-RII), inducible factor-1(HIF-1), Hypoxia inducible factor-2(HIF-2)in the plasma.

Fatigue is the most common symptom experienced by patients from cancer diagnosis to the end of life. CRF is different from other types of fatigue. It is severe, persistent and can not be alleviated by rest or sleep. CRF affects nearly 65% of cancer patients, more than two-thirds believe that severe CRF lasts at least 6 months, and one-third report that fatigue persists for several years after chemotherapy.

The etiology of CRF has not been fully elucidated, although it may involve several physiological and biochemical systems, which may vary with tumor type, disease stage and treatment. Recently, several cytokines and other proinflammatory mediators produced in tryptophan degradation and cancer response are associated with fatigue; however, their direct role in the pathogenesis of fatigue remains controversial. Cytokines may play a role at a variety of levels, including mood, muscle mass, strength and metabolic status, and thus are associated with the pathophysiology of fatigue. Recent studies have shown that fatigue is positively correlated with circulating levels of inflammatory markers, especially IL-6, IL-1 and neopterin, which are significantly correlated with CRF. CRF is also common in breast cancer patients, and the incidence rate of CRF is increasing as the incidence of breast cancer increases. In the treatment of breast cancer patients， chemotherapy can cause some patients' non hematological side effects such as fatigue. During the chemotherapy of breast cancer at high altitude area, clinical observation showed that the incidence rate of side effects after chemotherapy was higher in plateau area. Retrospectively analyzed the efficacy and safety of epirubicin combined with taxanes chemotherapy in the treatment of 48 cases of breast cancer in high altitude areas of Tibet. It was found that 89.5% of the patients with neutropenia after chemotherapy were significantly higher than those in low altitude areas, which also confirmed this phenomenon. The increased side effects of chemotherapy and radiotherapy in cancer patients at high altitude are closely related to hypoxia. The oxygen content and oxygen partial pressure in the atmosphere of plateau area also decrease with the increase of altitude, and the oxygen partial pressure in human alveoli also decreases, so the arterial oxygen partial pressure and saturation also decrease. A number of studies have shown that the special hypoxia environment at high altitude will have a lot of effects on the human body. In terms of cardiovascular system, it will make pulmonary hypertension and heart rate increase, and make the heart bear a heavy pressure load, leading to the occurrence of high altitude heart disease. In terms of nervous system, chronic hypoxia environment is prone to sleep disordered breathing at night, which seriously affects the brain nerve function and leads to heart failure sleep structure disorder. On the other hand, in order to adapt to the outside world, the human body in the plateau environment, within a certain limit, through the regulation of the nervous system and body fluid mechanism, carries out a series of adjustments and stress reactions, It makes a series of physiological changes in body fluid, hemorheology, blood biochemistry, blood gas and organ function, and some pathological changes, resulting in changes in physiological indexes, drug plasma protein binding rate, drug metabolic enzyme activity and expression, and inflammatory factors in blood. The investigators speculate that the above factors lead to the increase of side effects after chemotherapy at high altitude, especially the influence of inflammatory cytokines in the blood, leading to the occurrence of CRF.

Inclusion Criteria:

1. Female breast cancer patients aged ≥ 18 years old;
2. Breast cancer was confirmed by histopathological investigation;
3. Chemotherapy including neoadjuvant chemotherapy, postoperative adjuvant chemotherapy and palliative chemotherapy for advanced breast cancer;
4. Eastern Cooperative Oncology Group（ECOG ）score of physical condition (0-1);
5. Voluntarily participate in the clinical trial and sign the informed consent form after informed consent (patients voluntarily accept the test and give informed consent);
6. The basic indexes were consistent, and the blood routine and ECG were normal;
7. Before chemotherapy, fatigue scale was used to score, and no fatigue symptom was confirmed by CIS and BFI;

Exclusion Criteria:

1. Due to nervous system disease, difficulty in understanding and / or lack of personnel unable to complete the report;
2. The patients were treated with radiotherapy at the same time of chemotherapy; 3.There were no other tumors, and brain metastases and pleural effusion were excluded;

4.Women diagnosed with untreated anemia and thyroid dysfunction； 5.Heart and lung diseases were excluded; 6.The respiratory system diseases affecting blood oxygen saturation were excluded; 7.Fatigue symptoms were confirmed by cis and BFI.