Observational study on the tolerability, side effects, and efficacy of the approved drug combination of tucatinib, trastuzumab, and capecitabine

Breast cancer (mammary carcinoma) is a malignant disease of the breast gland tissue characterized by the uncontrolled proliferation of breast gland cells. Treatment depends on numerous factors, including the patient’s overall health, the tumor’s growth rate (Ki-67 index), the presence of hormone receptors on the cell surface (estrogen and progesterone receptor-positive), and the increased expression of the HER2 receptor (HER2-positive). The stage of the disease also plays a crucial role. While in the locally confined stage (stages 1–2A) the disease is limited to the breast, the locally advanced stage (stages 2B–3) is characterized by greater tumor spread or involvement of the lymph nodes. In Stage 4, metastases are present, meaning that the tumor has spread throughout the body. In this situation, palliative treatment is administered, which aims to “keep the disease at bay” for as long as possible.

Locally advanced, inoperable, or metastatic breast cancer can be treated, among other options, with combination therapy consisting of tucatinib, trastuzumab, and capecitabine. Tucatinib and trastuzumab specifically target the HER2 receptor, while capecitabine inhibits the growth of cancer cells. All three drugs are already approved for treatment.

The goal of this observational study is to collect additional treatment data on the combination therapy of tucatinib, trastuzumab, and capecitabine. The study is purely observational; no new drugs or therapies are being tested. Follow-up examinations will take place over a period of approximately two years, during which the effectiveness of the therapy, the occurrence of side effects, and the patients’ quality of life, among other factors, will be assessed.

Women and men aged 18 and older with locally advanced or metastatic (stages 2B–4) HER2-positive breast cancer are eligible to participate in this study. The disease must have been previously treated with at least two drug therapies targeting HER2.