Introduction
Today, chronic diseases and cancer are among the most important causes of death and disability in developed and developing countries, including Iran. Cancer is one of the most important diseases of the present century and the third leading cause of death after cardiovascular diseases and accidents. In recent years, the prevalence of cancer in developed countries has decreased, but in developing countries such as Iran, cancer has the highest growth rate in the world. Gastric cancer in Iran is the most common type of cancer in men. Today, the study of quality of life in cancer patients is considered an essential indicator of treatment and care worldwide. 
 The use of non-pharmacological treatments to improve the quality of life of gastric cancer patients can play a beneficial role in improving and increasing life expectancy. One of the most popular non-pharmacological interventions that patients well receive is the use of music as a therapeutic method. Listening to music is an affordable method with no side effects and invasiveness. It can successfully be used as a safe nursing intervention in hospitals for patients with chronic diseases. Music therapy can improve the quality of life and increase life expectancy in patients by reducing anxiety, stress, depression, and pain. Music therapy is a complementary therapy that improves the recovery and well-being of patients by increasing the stress threshold and eliminating negative emotions, regulating internal processes, creating a state of relaxation, and increasing immunity.
Methods
This study was an experimental study with a pretest-posttest design. The research population comprised all available patients with gastric cancer who met the inclusion criteria. They were selected from patients admitted to the Oncology and Chemotherapy wards of Imam Khomeini Hospital in Ardabil City, Iran, in 2020. The Cochran formula was used to determine the sample size at a significance level of 0.05 and with 95% power. The minimum required samples were 35 for the intervention group and 35 for the control group. Taking into account 5% sample loss (patient death), the sample size was 37 in each group. The patients were divided into control and intervention groups using the random allocation method. Each patient who met the inclusion criteria was assigned a number, and then with the help of a random number table, 37 patients were assigned to the intervention group and another 37 to the control group. Because of the limited number of patients admitted to the ward and the time interval between patients’ visits, which was close to one month, the groups had no information about each other. The research instruments included a 36-item quality of life questionnaire and a demographic information questionnaire. Music therapy was held for one month, five days a week, for 30 minutes daily. Two weeks After the end of the music therapy sessions, the patients in the intervention and control groups who were referred to the hematology ward of the hospital again completed the 36-Item Short Form Survey Instrument (SF-36) quality of life questionnaire.
Results
There were 22 men (59.5%) in the intervention group and 21 (56.8%) in the control group. The mean ± SD ages of patients were 53.38±14.00 years in the control group and 53.86±11.95 in the intervention group. The majority of participants, i.e., 26 (70.3%) in the intervention and 30 (81.1%) in the control group, were married. Also, most participants, i.e., 23 (62.2%) in the intervention group and 16 (43.2%) in the control group, had a diploma and lower educational status. The results of the Chi-square test did not show significant differences in gender, marital status, history of other diseases, and family support between the two groups. The results of the Chi-square test showed a significant difference in the number of children between the two groups (P=0.022). Also, the result of the independent t test shows no significant difference between the two groups of intervention and control in the mean age, occupational status, and duration of the disease. The result of the Mann-Whitney test did not show a significant difference between the two groups in terms of education level (P=0.054). A comparison of quality of life dimensions between the two groups of intervention and control after music therapy showed a significant increase in quality of life dimension scores (P˂0.05).
Discussion
The use of music in the treatment of cancer not only helps patients cope with the negative emotions caused by the disease but also improves many mental, emotional, social, and physical problems of cancer patients. Music therapy may not be effective in treating the disease itself, but it does greatly improve a person’s mood. Listening to music calms and reduces the stress caused by the disease. Music therapy allows patients to make positive mental and mood changes and solve their problems. Music therapy as a complementary therapy for rehabilitation of patients strengthens communication levels and physical coordination. It improves mental and physical functions in people who suffer from mental and physical problems due to chronic diseases. The use of music therapy has no side effects for patients, and it can be a cheap and available method along with medical methods or even alone in the focus of nurses and physicians. The use of music has advantages such as easy access, low cost, and non-invasiveness for patients compared to other medical methods. So, it can be used to accelerate the process of recovery and improve the health of patients. This study showed that music therapy improves the quality of life in cancer patients. Improving the quality of life in the experimental group supports this claim. Therefore, music therapy can be used in the Oncology Department to improve the quality of life.

Ethical Considerations
Compliance with ethical guidelines
This research was part of the student dissertation of the Master of Nursing of Islamic Azad University with the code of ethics IR.IAU.TMU.REC.1399.485. Ethical principles are observed in this article. Participants may well leave the study whenever they wish. Also, all participants were informed about the research process and their information was confidential.

Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors.

Authors' contributions
All authors equally contributed to preparing this article.

Conflicts of interest
The authors declared no conflict of interest.