Long-acting injections have outstanding contributions in prolonging the release period of drugs, reducing the frequency of administration, and improving the compliance of patients. Various long-acting schemes have been extensively studied, such as oil-based formulations, drug crystal suspensions, in situ forming implants, and microspheres. Among them, microspheres can load drug molecules with different properties through a variety of pathways, which have excellent prospects in drug delivery, especially as anticarcinogens. We have briefly summarized common biodegradable carrier materials for microsphere injections and their utilization in biological medicine, including natural, synthetic, and inorganic materials. Next, we have focused on deliberating the application of biodegradable microsphere injections in cancer therapy through marketed microspheres, clinical research, and experimental studies. At present, the use of microspheres in the treatment of cancers, such as prostate cancer, breast cancer, uterine fibroids, neuroendocrine neoplasm, and liver cancer, has been well-established. Finally, technical challenges and process difficulties in developing injectable microsphere products and viable solutions are briefly discussed. Microspheres have shown enormous potential in delivering anticancer drugs, and we believe that more types of microspheres will be used for cancer therapy in the future.