Yes; if the ancillary study adds an additional prospectively assigned intervention to patients or a sub-population of patients within the larger clinical trial and all elements of the NIH clinical trial definition are met.
No; if the ancillary study is only adding additional measures to an existing clinical trial.
Determine whether an ancillary study is a clinical trial by answering the four questions that define NIH clinical trials based on the information about the ancillary study alone, regardless of the clinical trial status of the parent trial.
For helpful examples, see new Clinical Trials Case Studies #42b and #42c. For more information on clinical trial definitions, check out our FAQs.