Are “data cut off” and “data lock” the same thing in a clinical trial?

Question

Quotes from a clinical trial report (JGOG3022 trial):

Follow-up was terminated in February 2017 and data were locked in October 2017. Of the 346 patients enrolled, ineligible patients and patients who did not receive bevacizumab were excluded, and the remaining 333 patients were classified as treated patients. They were divided into the primary analysis cohort (n = 293) and the exploratory analysis cohort (n = 40) (Fig. 1). The reasons for discontinuation of bevacizumab at the time of data cut-off were completion of the planned treatment schedule (34.8%), progression of the primary disease (26.6%), serious adverse events (14.0%), refusal by the patient because of adverse events (5.5%), and refusal by the patient for reasons other than adverse events (3.8%).

Do the authors mean the same by "data were locked" and "data cut off", or are these distinct procedures?

Answer 1

I don't think they are both specific terms that will apply consistently across all studies, you will have to use the surrounding context.

"Data lock" typically means that the data themselves in some sort of database are no longer being edited and are ready to be analyzed: that is, they have been recorded, checked for accuracy, etc. to create a "final" version. A synonym is "data freeze". It is usually referring more to the database itself, though, rather than data collection for the study. Indeed, in this passage, it seems like they finished collecting data in Feb 2017, but finalized the database in Oct 2017.

The purpose of a data lock/data freeze is to prevent statistical "fishing" in the data, for example by re-analyzing data until some significance threshold is reached, or making decisions about exclusion criteria after preliminary statistical analyses have been completed. The proper procedure is to get your data in the best condition they can be in, and then begin analysis.

The only sensible interpretation of their meaning of "data cut-off" in this context is that it refers to the end of the follow-up period in Feb 2017: since follow-up stopped then, they wouldn't know reasons for discontinuation past then. The study is frozen in time at the time they stopped recording data. I am not aware of this phrase being used as a specific term (unlike data lock or data freeze), I think they are just using the general English meaning of those words to describe "the time after which we didn't collect any more data."