Background: Our aim was to determine the frequency of health-related problems faced by breast cancer patients before and six months after the initiation of breast cancer treatment. Methods: This prospective study involved 600 female breast cancer patients (26-65 years, mean 52), who participated in the pilot study in the novel individualized integrated rehabilitation programme in 2019-2022 and were followed for at least six months. The patients completed three questionnaires (EORTC QLQ - C30, B23 and NCCN) before the initiation of cancer treatment and six months after. The patients received neoadjuvant chemotherapy in 22% of the cases, tumorectomy in 53%, mastectomy in 39%, breast reconstruction in 27%, sentinel node biopsy in 67%, lymphadenectomy in 23%, external beam radiotherapy in 73%, chemotherapy in 45%, anti-HER-2 therapy in 11% and hormonal therapy in 74% of the cases. Data on the patients’ demographics, disease extent, cancer treatment and problems reported in the questionnaires were collected and analysed using descriptive analysis. Results: The problems reported by patients before the initiation of cancer treatment and after six months are presented in Table. In 14 out of 22 parameters, the frequency of problems increased in the six months after the initiation of treatment: fatigue, insomnia, lymphedema, shoulder movement impairment, disturbing scars, heart problems, hot flashes/sweating, gynaecological problems, sexual problems, body image worries, inappropriate nutrition, pain in the shoulder or arm, alopecia and concerns about returning to work. On the other hand, the frequency of problems decreased six months after the initiation of cancer treatment in 6 out of 22 parameters. Our patients less often had depression or anxiety, were too little physically active, smoked, consumed alcohol or used food supplements than before. Conclusions: Six months after the initiation of breast cancer treatment patients have more problems than at the time before treatment.