Last updated on March 27, 2019
Clinical trials are research studies that test a new drug or therapy in patients who have a disease. These studies are classified as phase I, II, or III depending on their purpose.
Phase I: These initial, small studies test promising new drugs that effectively kill cancer cells in laboratory experiments. The goal is to understand the safe dose and capture early evidence of benefit. Phase I trials may be open to patients with any type of cancer, or only certain types of cancers more likely to respond to specific drugs. Generally, fewer than 50 patients are enrolled.
Phase II: Once a phase I trial identifies a safe dose, a phase II trial is done to better understand the potential benefit and side effects of the drug. Generally, these studies enroll fewer than 100 patients.
Phase III: If the new treatment has promising activity in the phase II trial, the next step is usually a phase III trial comparing it with an existing standard treatment. If there is no standard treatment, patients may be randomly assigned to receive either the new treatment or a placebo (such as a sugar pill). Generally, phase III trials are large. The researchers may enroll many hundreds of patients, or even more than 1,000, to establish whether the new treatment is an advance over standard treatment and warrants US FDA approval. Many immunotherapy drugs have been approved in recent years to treat different cancers based on phase III trials showing improved survival compared with previous standards of treatment. A few examples are pembrolizumab (Keytruda) for metastatic bladder cancer, and ipilimumab (Yervoy) combined with nivolumab (Opdivo) for kidney cancer and melanoma.