Caldwell said the DHB didn't have "robust systems" set in place to minimise risk and make sure patients were getting booked in for important follow-up care.
She found it breached multiple rights, including the right for Mr A to access his results and effective communication between the DHB and Mr A after his 2019 surgery.
Mr A's daughter made the complaint in 2020, after her father was diagnosed with terminal bladder cancer.
In 2021 the family told the HDC his cancer had since moved to Mr A's lymph-nodes and was unsurvivable.
Mr A was in his early 60s when he went to his GP on January 11, 2019, reporting he blood in his urine.
Four days later his GP referred him to the local outpatient urology service for further testing which was completed on January 18.
Results showed he had a "high-grade non-invasive tumour" on his bladder, and doctors noted there was now a high suspicion of cancer.
Futher tests revealed there were two tumors on Mr A's bladder.
After a meeting with a urologist on February 7, Mr A underwent surgery a month later at Nelson Hospital.
A management plan was recorded after the surgery, including directions for an outpatient follow-up two to three weeks post-surgery.
This follow-up never happened.
The registrar recorded the direction in both handwritten clinical notes and in a dictated note on the day of the surgery, however, it was not uploaded to the electronic record for almost two weeks.
Mr A was also told he would be given information about the surgery, but this did not happen.
It was found in Mr A's histology that the tumours were cancerous and could grow rapidly and spread.
The DHB told the HDC this was to be discussed at the follow-up appointment that never occurred.
In light of the complaint, the DHB opened an internal investigation into how Mr A slipped between the cracks.
It was initially unclear why this happened, but it was later found the appropriate email was never sent.
More than a year later, in April 2020, Mr A reported "noticeable blood in his urine" and "occasional discomfort" to his GP.
Due to the Covid-19 lockdown at the time, Mr A had an over-the-phone consultation a few days later.
He had been experiencing reoccurring symptoms for several months after surgery, and on May 21, 2020, went to the urology registrar who acknowledged a follow-up never eventuated.
The registrar examined Mr A's bladder, where they found "extensive abnormalities". He was later diagnosed with terminal bladder cancer and began chemotherapy in September 2020.
Caldwell said the tumour had progressed to become a muscle-invasive metastatic disease, which may have been preventable had Mr A received a timely follow-up after surgery.
In June 2021, Mr A and his family told the HDC the cancer had spread to his lymph nodes, which was diagnosed as incurable and terminal.
The Nelson Marlborough District Health Board acknowledged that it had failed to deliver "appropriate follow-up care" and apologised for the harm they had caused Mr A and his family.
A written apology from the DHB to Mr A was recommended by Caldwell for the failings that potentially led to the terminal cancer.
Caldwell also recommended the DHB outline any progress that has been made since the failure.
