Romiplostim is used in cancer patients primarily when they experience thrombocytopenia that is not adequately managed by other treatments. It is especially helpful for patients with chronic ITP who have not responded to other therapies such as corticosteroids, immunoglobulins, or splenectomy. Additionally, it is considered when chemotherapy-induced thrombocytopenia impedes cancer treatment, as maintaining adequate platelet counts is crucial for the continuation of cancer therapies.