Feasibility of Switching to a High-Fiber, Gut-Healthy Diet in Women with Triple-Negative Breast Cancer During Neoadjuvant Immunotherapy and Chemotherapy

Breast cancer (mammary carcinoma) is a malignant disease of the breast gland tissue characterized by the uncontrolled proliferation of breast gland cells. Treatment of the disease depends on numerous factors, such as the patient’s overall health, the stage of the disease, the presence of detectable hormone receptors on the surface of the cancer cells (estrogen receptor- or progesterone receptor-positive) and the increased presence of the HER2 receptor on the cells (HER2-positive). In triple-negative breast cancer, the tumor cells express neither estrogen nor progesterone receptors and do not show increased expression of the HER2 receptor. Compared to other forms of breast cancer, it often carries an increased risk of recurrence and a greater tendency to form secondary tumors in other organs (metastases). In the early stages of the disease, immunotherapy and chemotherapy can be administered before surgery (neoadjuvant therapy). Immunotherapies are designed to help the body’s own immune system recognize tumor cells as abnormal and fight them. The bacteria in the gut (microbiome) and the immune system influence each other: Dietary fiber, found primarily in plant-based foods, is broken down (fermented) by bacteria in the gut, producing, among other things, so-called short-chain fatty acids. Based on current knowledge, these can also affect immune system cells. Research on the microbiome suggests that a high-fiber diet could alter the gut flora in a way that might influence the response to and tolerability of therapy. However, this hypothesis has not yet been confirmed.

The aim of this study is to examine whether switching to a high-fiber, gut-healthy diet during immunotherapy and chemotherapy is feasible in practice. As part of the study, patients will be randomly assigned to two parallel groups. In the study arm, they will be supported in the transition to a high-fiber diet by a team of specialized physicians, nutritionists, and mind-body therapists. Support from these professionals will take the form of office visits, individual consultations, and an online group training program. Mind-body medicine encompasses approaches designed to help patients cope with stress and change their behavior and lifestyle. In the control arm, patients receive standard care in the form of an information sheet and an educational video containing the dietary recommendations of the German Nutrition Society (DGE). The study is open-label (not blinded), meaning that both the patients and the study physicians know who has been assigned to which group.

Women aged 18 to 75 with non-metastatic triple-negative breast cancer (stages 1 through 3) who are scheduled to undergo chemotherapy and immunotherapy prior to surgery are eligible to participate. Patients for whom health or practical reasons preclude a high-fiber diet or participation in online group training are not eligible to participate.