There is an increase in the number of patients with secondary malignant neoplasms. In addition, in some subgroups after radical cancer treatment, the lifetime risk of developing secondary malignant neoplasms can be as high as 33 %. Secondary malignancies remain an important cause of death in patients who have received radical cancer treatment. The presented clinical case demonstrates the risk of developing primary multiple malignant neoplasms after radiation therapy and chemotherapy. A 39‑year-old patient with diffuse large B-cell non-Hodgkin lymphoma underwent definitive treatment including chemo-and radiotherapy. Ten years later, the patient developed the induced multiple malignant tumors: a malignant neoplasm of the heart — myofibrosarcoma of the right ventricle with invasion of the anterior wall of the right ventricle Stage IIIB G2T3N0M0, left breast cancer Stage IIIA T3N2M0. The choice of treatment tactics for this category of patients remains particularly difficult.