There are no accurate figures for how many cancer patients in Wales have a key worker co-ordinating their care.
The Welsh Government said in May 2010 health boards should ensure key workers - who help co-ordinate patients' care - were in place by the end of March 2011.
Public Health Wales (PHW) said collection of that data was "not currently mandatory".
The Welsh Government said a set of standards and measures to review progress was being developed.
A Freedom of Information (FoI) request was submitted after some cancer patients contacted BBC Wales to say they had not been allocated a key worker.
But PHW said "understanding of what numbers and percentages of patients with a key worker is not possible to collate" as data did not have to be collected.
It said the most recent All Wales Cancer Patient Survey - which asks whether patients have a key worker - was due for publication later this month.
"This survey therefore should give a percentage of compliance both nationally and by health board, the only rider being that it will of course reflect the response from the percentage of patients who decided to respond to the actual survey," the statement added.
PHW said it was not in the public interest to release data from the most recent survey early as it needed to be collated and verified.
Susan Morris, from Macmillan Cancer Support in Wales, which carries out the survey, said: "More robust monitoring of the situation on the ground would be welcome to ensure this commitment is being met."
"Our 2014 Wales Cancer Patient Experience Survey, which Macmillan ran with the Welsh Government, showed a third of the 7,352 people with cancer surveyed (34%) were not given the name and contact details of a key worker.
"As a single point of contact they help ensure people diagnosed with cancer can access the right information and support, while also helping them to navigate complex care and treatments."
Prostate cancer patient Nick Phillips, 59, from Pontypridd, Rhondda Cynon Taff, who says he has not been assigned a key worker, said: "They shouldn't be relying on the patient survey, it's not an accurate reflection. Not everybody is going to reply.
"We want to know the figures. Every patient should be having a key worker and a care plan."
Carolyn Robertson, 70, from Whitchurch in Cardiff, added: "It's sad they don't know the numbers of key workers.
"I've talked about how beneficial it was in the case of my breast cancer. I've had the care that helped me survive, that's why I'm banging the drum."
A Welsh Government spokesman said: "The Cancer Implementation Group, which is responsible for the delivery of the Cancer Delivery Plan, has identified the key worker role as a priority.
"As such, work is currently being undertaken to develop a set of standards and associated measures to review the progress health boards and trusts are making in the provision of key workers, as well as for other priority issues."