Belotecan hydrochloride is primarily used in the treatment of small cell lung cancer (SCLC) and ovarian cancer. It functions as a topoisomerase I inhibitor, which helps in preventing cancer cells from replicating by interfering with their DNA replication process. This makes it effective in slowing down or stopping the growth of cancer cells. It is often administered intravenously in clinical settings as part of combination chemotherapy regimens. Due to its targeted mechanism, it is particularly useful in cases where other treatments have not been effective. However, it may cause side effects such as neutropenia and gastrointestinal issues, requiring careful monitoring during therapy.