Objective: Case management (CM) programs are intended to improve care coordination for cancer patients. This quasi-experimental, controlled study evaluated whether such a program was effective in improving health-related quality of life and reducing the psychological distress of breast cancer patients. Methods: For the study, 126 patients with CM and 118 patients with treatment as usual (TAU) were surveyed at baseline, a 6-month follow-up and a 12-month follow-up. Comparisons of the two groups with regard to quality of life (Short Form-8, European Organization for Research and Treatment of Cancer-11; primary outcome) and psychological distress (Hospital Anxiety and Depression Scale, distress thermometer; secondary outcome) were conducted. Results: Univariate t-tests regarding the primary and secondary outcomes demonstrated improvements in the relevant outcomes at the 6-month and 12-month follow-ups for the intervention group as well as for the control group. An analysis of covariance revealed that the controls showed a higher level of physical quality of life at the 12-month follow-up than the other time points and no differences at 6 months after the baseline. Conclusions: The tested CM model did not improve the quality of life or psychological well-being of the patients beyond treatment as usual. Possible reasons include that the treatment was already of high standards in the control group or that there are possibly different impacts than found in the literature regarding different forms of organization in CM. The need for and the tailoring of this CM model as well as the transfer of CM to other oncological indications remain to be clarified.