In the clinical research trial industry,<unk>  refers to patients who at one point in time were actively participating in a clinical research trial, but have become<unk>  (either by error in a computer tracking system or by being unreachable) at the point of<unk> -up in the trial. These patients can become<unk>  for many reasons. Without properly informing the investigator associated with the clinical trial, they may have opted to withdraw from the clinical trial, moved away from the particular study site during the clinical trial, became ill and unable to communicate, are missing or are deceased.
Lost to follow-up
Serious adverse event
Terminal illness
Natural history of disease
Risk factor
Adverse event
Unwarranted variation
Immune-related response criteria