Clinical Trials Glossary

As a patient with cancer, you will be dealing with new terms on a day to day basis. Here we offer some information on some of the many acronyms and unfamiliar terms you will encounter.


Activities of Daily Living. These are activities that a person normally does on a daily basis to maintain their life, such as nutrition, personal hygiene and other activities that provide for their physical and social well being.


Adverse Event or Adverse Effect. An unexpected or undesirable effect of a drug. This could be, for example, diarrhea, nausea, vomiting, fatigue or skin reactions. These adverse effects can interfere with the activities of daily living.


A small group of individuals with some characteristics in common. In Phase 1 clinical trials, the individuals in a particular cohort all receive the same dose of the treatment being studied.


Most Responsible Physician. This is the physician who oversees your medical care.


Maximum Tolerated Dose. This level of treatment is found when a set number of people in a cohort experience unacceptable toxicity from the dose level. The dose is then decreased to the level of the previous cohort. This is this dose of the treatment which is considered to be safe; in other words, it is the maximum dose which is not considered to be too toxic. Also known as MDL - Maximum Dosage Limit.


Severe Adverse Event or Effect. This is a reaction that can be permanently injurious or cause death. Also known as SADR - Serious Adverse Drug Reaction.

Starting Dose

The dose chosen to treat the first cohort of patients in a Phase I trial — determined by the dosage that lab animals were able to tolerate.

Dose Increment/Decrement

The percent increase or decrease between dose levels.

Dose-Limiting Toxicity (DLT)

Toxic side effects that are presumably related to the drugs and are considered unacceptable — because of their severity and/or irreversibility — and that limit further dose escalation. DLTs/toxic effects which the trial’s sponsor expect to occur are acknowledged in the sponsor’s/investigator’s brochure before beginning the trial and are protocol specific

Dose – Efficacy Curve

The dose – efficacy curve reflects the relationship between dose and probability of efficacy for an anticancer agent.

Dose – Toxicity Curve

The dose – toxicity curve reflects the relationship between dose and probability of toxicity for an anticancer agent.

Target Toxicity Level

The maximum probability of Dose-Limiting Toxicity (DLT) that is considered acceptable in the trial. The target toxicity level in Phase I trials is typically 20%- 33%.

Maximum Tolerated Dose (MTD)

In Phase I trials conducted in the United States, MTD is the highest dose level at which ≤ 33% of patients experience DLT (a misnomer in the sense that the MTD is actually not a tolerable dose).

Optimal Biological Dose (OBD)

Dose associated with a pre-specified most desirable effect on a biomarker among all doses studied (e.g. inhibition of a key target in tumor or surrogate tissue or achievement of a pre-specified immunologic parameter). Phase I trials in which the endpoint is a pre-specified biological endpoint: the OBD.


Pharmacologic effects of the body on the drug (i.e. the time course of drug absorption, distribution, metabolism, and excretion).


Pharmacologic effects of the drug on the body (e.g. nadir neutrophil or platelet count, non-hematologic toxicity, molecular correlates, imaging endpoints).