Background: Cancer patients commonly experience pain. Advanced breast cancer patients experience pain due to the involvement of other structures, as well as due to the cancer treatment. Transcranial magnetic stimulation is a new non-invasive brain stimulation method for pain management. This treatment has been proven to decrease the visual analogue scale pain score and to increase the serum beta-endorphin level in other chronic pain patients. Objective: To study the effect of transcranial magnetic stimulation on pain intensity, opioid usage, and serum beta-endorphin levels in breast cancer patients. Design: Prospective, randomized controlled trial. Setting: University Hospital Patients: Forty admitted and outpatient breast cancer patients, divided into groups P1 and P2. Intervention: The P1 group received 10-Hz transcranial magnetic stimulation for 20 minutes, at 80% of the motor threshold, with 100 pulses/train to 20 pulses/session, and with a 50 second intertrain interval. The P2 group was the control group. Five sessions of transcranial magnetic stimulation were administered, with one session per day, by a researcher or assistant. Main outcome measures: After five sessions or at the end of the session, the pain intensity of patients was re- examined using a numerical rating scale, and the opioid usage and the serum beta-endorphin level in the blood post-treatment was documented. Results: The decrease in the numeric rating scale score was larger in group P1 than in group P2 (p < 0.001). Opioid usage was less in group P1 than P2 (p < 0.024). Moreover, serum beta endorphin levels had increased in group P1 as compared to group P2 (p < 0.001). Conclusions: Transcranial magnetic stimulation can decrease the pain intensity and opioid usage, and increase the serum beta-endorphin level in patients with breast cancer-related pain. Trial registration Clinicaltrials.gov identifier: