The review was expected to be completed in January, but board chief executive Chris Fleming, responding to questions asked more than a month ago, said the initial interviews and data collection had been completed and reviewers were working on preparing the report.
"Reviews can take time and we want to ensure the process adequately covers the issues in question."
In response to further questions, Mr Fleming said there was no time set for the completion of the final report as "there are still a number of issues to work through".
Under the terms of reference for the report, it is to be circulated to all participants before finalisation to allow them to check its accuracy. Mr Fleming said he expected "this to occur soon".
The review, being carried out by Christchurch clinicians, retired general surgeon Phil Bagshaw, and gastroenterologist Dr Stephen Ding, was announced in October.
It had been in the pipeline since 2017, following ongoing concerns raised by Southland general surgeons about what they described as a "very high incidence" of missed colorectal cancers in patients whose referrals for a colonoscopy had been declined.
The terms of reference for the review said the timeframe for it was expected to be eight weeks.
Up to 102 referrals where concerns had been raised about the process followed were to be included in the review. These would include at least 20 cases where surgeons believed cancer diagnosis was delayed.
