Music therapy in cancer patients, as a complementary psychological intervention, is based on the purposeful use of musical elements to modulate emotion, reduce distress, and promote adaptation to the disease. The theoretical foundations of this approach emphasize the interplay of cognitive, emotional, physiological, and social processes. Music can help regulate the patient's psychological responses through altering arousal, attention, mood, and emotional processing. From a psychophysiological perspective, rhythm, melody, harmony, and speed of music can be related to the arousal of the autonomic nervous system and indicators such as heart rate and muscle tension. Music is also able to divert the patient's attention from threatening thoughts and ruminations associated with cancer. In the context of emotion regulation, the musical experience can help identify, express, and moderate difficult emotions such as fear, sadness, anger, and frustration. Music also allows for non-verbal expression of experiences that the patient may not be able to express directly in a conversation. In psycho-oncology, this feature is especially important because the experience of cancer is often associated with uncertainty, lack of control, changes in body image, and worry about the future. Research evidence has shown that music-based interventions in some groups of cancer patients can be associated with reduced anxiety and psychological distress and improved mood. Some studies have also reported a reduction in pain and fatigue perception and improved quality of life. Systematic reviews and meta-analyses generally support the potential effectiveness of music therapy for reducing certain psychological and physical symptoms, although the effect is not the same in different studies. In some clinical research, music therapy during periods of chemotherapy has been associated with a reduction in pre-treatment anxiety and an increase in patient relaxation. Guided listening to music has also been studied in some studies as a simple way to reduce tension and create a sense of control. Active music therapy, such as singing, improvisation, or making music, allows for direct patient participation and strengthens psychological agency. In contrast, receptive interventions focus more on purposeful listening and creating a state of relaxation. Choosing music that suits the patient's individual preferences can be effective in creating a sense of security, familiarity, and emotional connection. The use of music therapy has been considered in managing anxiety, managing pain, reducing fatigue, improving sleep, and improving quality of life. This intervention can also play a complementary role in the patient's psychological preparation prior to diagnostic or therapeutic measures. In children with cancer, age-appropriate musical activities can provide opportunities for play, connection, and emotional expression. In adults, music can also help maintain identity, positive memories, and social connection. In palliative and end-of-life care, music therapy is sometimes used to support communication, reduce distress, and facilitate the expression of emotions and meaning. From a clinical perspective, music therapy should not replace standard oncological or psychological treatments, but rather should be used as part of comprehensive, multidisciplinary care. One of its important uses is to accompany interventions such as relaxation, cognitive-behavioural therapy, mindfulness, and psychological support. Music can also help regulate arousal levels before starting a psychological intervention. However, the available evidence faces limitations such as small sample sizes, heterogeneity of protocols, and differences in the type of cancer and stage of the disease. Differences in music choice, duration of sessions, number of sessions, and specialty of therapists also make it difficult to compare the results of studies. Some research has used listening to music, while others have focused on active musical interventions. This heterogeneity makes it prudent to generalize the results to all patients with cancer. The patient's cultural and individual preferences can also affect the response to music. Music that is relaxing for one patient may cause unpleasant memories or intense emotional reactions in another patient. Therefore, it is important to assess the patient's musical history, preferences, and sensitivities prior to intervention. Other challenges include the difficulty of standardizing music therapy interventions. Outcome measurement should also be carried out with valid measures of anxiety, depression, pain, fatigue, and quality of life, in addition to subjective indicators, if possible. The use of validated tools allows for a more detailed comparison of studies and an assessment of the actual effectiveness of the intervention. Another limitation is the short-term nature of many studies and the lack of data on the persistence of effects at long-term follow-up. It is also unclear which component of music or presentation plays the most role in emotional changes. Future research can reduce these uncertainties by designing randomised trials with larger samples. It is also necessary to investigate the differences in patients' responses based on type of cancer, stage of disease, age, gender, psychological characteristics and cultural context. Combining music therapy with digital technologies and teleinterventions can increase patients' access to psychological support. The use of physiological indicators such as heart rate and heart rate variability can also help to examine emotion regulation more closely. Overall, clinical evidence suggests music therapy as a complementary and relatively low-risk intervention to support emotion regulation and reduce some dimensions of distress in patients with cancer, but the heterogeneity of the studies and the limitation of the evidence preclude definitive conclusions about how effective it is in all patients.