A Welsh Government target to treat suspected cancer patients within 62 days has been missed by 10%, figures have revealed.
The target was for 75% of patients to start treatment with 62 days of first suspecting a cancer diagnosis.
But figures show just over 65% of patients were treated within that time.
It is the first time such figures have been published following the launch of the 'single cancer pathway', which was designed to cut waiting times through more accurate data.
Cancer charities have welcomed the pathway, claiming it will better reflect the state of cancer services across Wales.
But they warned that there has been a drop in the number of people seeing their GP when experiencing symptoms.
Figures for December 2020 revealed:
1,345 patients started first definitive treatment on the suspected cancer pathway in the month of December 2020
Of these, 882 patients started treatment within 62 days from point of suspicion
This is up 2.1% from November 2020
7,999 patients were confirmed as not having cancer
Cancer Research Wales' Chief Executive, Ann Tate, said: "The move towards a single cancer waiting time measure is a welcome development.
"However, my feelings towards today’s single cancer pathway news are tempered by the drop in the number of people coming forward to talk to their GP about cancer signs and symptoms.
"People have kept their distance out of fear of burdening the NHS, or out of a concern for catching coronavirus. The NHS across Wales has taken a number of steps to ensure you are able to speak to or visit your doctor as safely as possible.”
Ms Tate urged those concerned about potential cancer symptoms to contact their GP.
Health minister Vaughan Gething reiterated that message, and said: "We want to ensure that anyone who is suspected of having cancer in Wales has access to timely and appropriate treatment that will deliver the best possible outcome, or be told as soon as possible that they do not have cancer.
"While the figures published today are below the target of 75% that has been set, they are a much more accurate way to measure how long it takes for a suspected cancer to be referred, investigated and for treatment to be started.
"We know much more work is needed to improve performance."
The figures come as wider referral to treatment times have revealed a record number of patients in Wales are currently waiting for treatment.
The number of patients waiting to start treatment is at a record high of 538,861, with 226,138 patients waiting more than the 36 week government target in December 2020.
The Royal College of Anaesthetists said this further highlights the "devastating impact" of the pandemic on waiting lists in Wales.
Dr Abrie Theron, Chair of the Welsh Board, called on the Welsh Government to ensure restrictions continue to reduce the numbers of Covid patients in hospitals.
He said: "Addressing waiting lists must be at the heart of any Covid recovery plan for NHS Wales, especially as a backlog this size will already take years to clear.
"We must remain able to manage Covid demand whilst continuing and increasing the availability of routine care.
"This is paramount if clinicians and healthcare workers are to have any chance of starting to work through this backlog of patients who desperately need treatment."
The Welsh Government is expected to announce marginal changes to lockdown restrictions on Friday.