Key Terms Associated with Clinical Trial Phases

The following terms are often used in discussions of a clinical trial and its phases.

• Accrual –  The process of enrolling patients in a clinical trial, or the number of patients already enrolled or anticipated to be enrolled in a clinical trial.
• Arm – A treatment group in a randomized study, in which there are two or more arms.
• Cohort – The arm of a randomized clinical trial that receives the standard of care of treatment or placebo.
• Control group – The arm of a randomized clinical trial that gets the standard treatment or placebo (no treatment).
• Dose-limiting toxicity (DLT) – When the side effects of the treatment are severe enough to prevent giving more of the same treatment. 
• Double-blind – When neither the patient nor the investigator knows the arm of the trial to which the patient is randomized. The purpose is to report any bias in the reporting results.
• Endpoint – The goal of the study. A clinical trial endpoint may aim to measure toxicity, response rate, or survival.
• Experimental group – The arm of a randomized trial that gets the new treatment.
• Maximum-tolerated dose (MTD) – The highest dose of a treatment that most people can safely withstand.
• Placebo – An inert (inactive) substance often used in clinical trials for comparison with an experimental drug. No clinical trial for cancer patients in the U.S. can ethically or legally randomize patients to receive a placebo alone when they require treatment. In the placebo arm of a cancer treatment trial, patients receive treatment with approved therapy plus a placebo.
• Progression-free survival (PFS) – The length of time during and after the treatment of myeloma that a patient lives with the disease but the myeloma does not get worse. In a clinical trial, PFS is one way to measure how well the treatment is working.
• Progressive disease –  Myeloma that is becoming worse or relapsing, as documented by tests. Defined as an increase of ≥ 25% from the lowest confirmed response value in the myeloma protein level and/or new evidence of disease.
• Randomized clinical trial – A study in which patients are randomly assigned to receive a particular treatment.
• Refractory –  Disease that is no longer responsive to standard of care treatments. Myeloma is refractory in patients who have had progressive disease either during treatment or within 60 days following treatment. Most clinical trials for advanced disease are for patients with relapsed and/or refractory myeloma.