Irinotecan is primarily used in the treatment of colorectal cancer, often in combination with other chemotherapy drugs like 5-fluorouracil and leucovorin. It is particularly effective in cases where the cancer has metastasized or recurred after initial treatment. The drug works by inhibiting topoisomerase I, an enzyme crucial for DNA replication, thereby preventing cancer cells from multiplying.

In clinical practice, it is administered intravenously and is part of first-line therapy for advanced colorectal cancer. It is also used in the treatment of certain types of lung cancer and has shown efficacy in some cases of pancreatic cancer. Due to its mechanism of action, it is particularly useful in targeting rapidly dividing cancer cells, though it can also affect healthy cells, leading to side effects such as diarrhea and neutropenia.

Additionally, Irinotecan is sometimes used in palliative care to alleviate symptoms and improve quality of life in patients with advanced cancer. Its application is carefully monitored, with dosage adjustments made based on patient response and tolerance to minimize adverse effects while maximizing therapeutic benefits.