Background/Aim: Breast cancer patients receiving radiation therapy (RT) may experience considerable distress. We investigated the course of distress during an RT-course for breast cancer. Patients and Methods: Three-hundred-andthirty breast cancer patients completed Distress Thermometers before and directly after RT. Distress was evaluated in the entire cohort and different groups of age, sex, Karnofsky performance score (KPS), intent of RT, and previous RT. Results: Mean change of distress scores was -0.4 points, which was significantly associated with KPS. Decrease of distress was more pronounced in patients with KPS ≤80 or age <64 years. Deterioration (yes vs. no) was non-significantly associated with no previous RT. In patients with pre-RT distress scores ≤5 points, mean score increased by +0.5 points; no significant associations between characteristics and investigated endpoints were found. Conclusion: Psychological assistance should be offered to all patients irradiated for breast cancer, particularly to those with risk factors, regardless of the pre-RT distress score.Breast cancer is the most common primary tumor type among women in Western countries (1). Many of these patients receive radiation therapy (RT), either as loco-regional treatment following breast surgery or for metastatic disease. Anticipated treatment may induce considerable distress for the corresponding patients. In a previous study of breast cancer patients assigned to adjuvant RT following breastconserving surgery or mastectomy, 46% of patients reported fears prior to the start of RT, 38% worry, 29% sadness, and 29% nervousness (2). These emotional problems are part of the National Comprehensive Cancer Network Distress Thermometer (NCCN-DT) (3). In the study of Mose et al., 48% of patients assigned to adjuvant RT of early-stage breast cancer reported distress related to the upcoming RT (4). In addition, Goldschmidt Mertz et al. found that 43% of patients with newly diagnosed breast cancer felt distressed, when a cut-off value of 7 points on the NCCN-DT (points range between 0 and 10, with 10 points indicating maximum distress) was used (5). When using a cut-off value of 3 points, even 77% of the patients were considered distressed. The highest rates were observed for worry and nervousness (5). Luutonen et al. found depressive symptoms and distress in 32% and 28% of breast cancer patients treated with adjuvant RT (6). Moreover, Browall et al. have shown that emotional functioning is positively correlated with the quality of life of patients receiving adjuvant RT for breast cancer (7).Current literature demonstrates that emotional and psychological distress are common in breast cancer patients assigned to RT. However, little is known regarding the course of distress scores during an RT-series. In a previous study including different types of malignancy, the change of distress during the RT-course was significantly associated with the primary tumor type (8). Therefore, it was considered reasonable to perform separate studies for the most com...