Combined Exercise is Best Exercise Modality to Improve Quality of life in Breast Cancer Survivors: A Systematic Review and Meta-Analysis

: A single paragraph of about 100 words to give a brief introduction to your work Abstract: Globally, breast cancer is the most common cancer in women, posing a serious threat to women’s health. We investigated the different types of exercise( aerobic exercise (AE), resistance exercise (RE), and combined aerobic and resistance exercise (CO)) to increase the quality of life (QoL) in breast cancer patients. Meta-analysis was used to estimate the effect sizes, and subgroup analyses were conducted based on types of exercise. The inclusion criteria were met by 28 studies (31 trials), comprising 2038 patients for exercise (n = 1039) and control (n = 999). Meta-analysis showed exercise intervention enhanced QoL (0.44; 95% CI: 0.26–0.62) in patients with breast cancer. Subgroup analysis revealed CO (0.97; 95% CI: 0.33–1.61) was better than AE (0.42; 95% CI: 0.17–0.67) and RE (0.13; 95% CI: −0.05–0.31) in increasing QoL in patients. In conclusion, exercise intervention has a positive impact on the QoL of breast cancer patients. The most appropriate type of exercise to improve QoL is probably CO.


Introduction
Globally, breast cancer is the most common cancer in women, posing a serious threat to women's health.About 2.1 million new cases of breast cancers were diagnosed in 2018, accounting for one quarter of cancer cases in women [1].Fortunately, owing largely to early detection and the development of medical technology, the survival rate of breast cancer patients after treatment is increasing [2].However, the treatment of cancer produces a series of side effects (e.g., nausea, pain, insomnia, and limited limb movement), which seriously affect the quality of life (QoL) of cancer patients [3,4].
As a physical therapy, exercise has been included in the rehabilitation of breast cancer patients.Previous studies have shown that exercise intervention can change patients' body composition, enhance muscle strength, regulate mood, and increase QoL [5,6].However, It is not clear which type of exercise is better for increasing the QoL of breast cancer patients.A meta-analysis of 25 RCTs found that a single type of exercise intervention, such as aerobic, yoga, or qigong, is more conducive to improving the QoL of breast cancer patients than combined aerobic resistance exercise [7].An RCT on exercise and breast cancer patients reported that there was no difference between aerobic exercise (AE) and combined aerobic and resistance exercise (CO) in improving the QoL of breast cancer patients [8].Another RCT indicted that resistance exercise (RE) and AE have the same effect on improving the QoL of breast cancer patients [9].Therefore, the main purpose of this systematic review and meta analysis was to evaluate the efficacy of the different types of exercise intervention on the QoL of breast cancer patients.

Search strategy
The electronic databases we used to search for literature included PubMed, Sci-enceDirect, Google Scholar and Web of Science.We conducted the electronic search form database inception to November 2020.The search terms included "breast cancer" OR "breast tumor" OR "breast neoplasms" AND "sports" OR "physical activity" OR "exercise" OR "aerobic exercise" OR "resistance exercise" AND "quality of life" OR "QoL".

Study Searching and Selection
Through a systematic search, a total of 1605 studies were identified.After removing duplicates, 764 studies remained.After reading titles and abstracts, 662 articles were excluded, and 102 potentially relevant studies remained.Finally, we checked the 102 full texts, removed 74 articles, and included 28 studies (31 trials) in our meta-analysis (Figure 1).

Study Characteristics
The detailed characteristics of the 28 studies (31 trials) are presented in Table 1.A total of 2038 patients with breast cancer were included in these studies.The sample size included studies ranging from 16 to 242, and published between 2003 and 2016.The mean age of patients was between 26 and 78 years old.

Effect of Exercise Intervention on QOL for Breast Cancer Survivors
Data from 28 articles (31 trials) were pooled for analysis.The result of meta-analysis showed that the change in QoL was extremely favourable for the exercise intervention group with heterogeneity Tau 2 = 0.18; Chi 2 = 114.13;degrees of freedom (df) = 30; I 2 = 74%, and the combined SMD (95% CI) was 0.44 (0.26-0.62).Due to the high heterogeneity, the random-effects model was used (Figure 2).

Conclusions
In summary, our findings show that exercise intervention may increase self-reported QoL in breast cancer patients.The most appropriate type of exercise to improve QoL is probably CO.
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Figure 1 .
Figure 1.Flow chart of literature search.

Figure 2 .
Figure 2. Meta-analyses of the impact of exercise on QoL.

Table 1 .
Characteristics of the included studies.