The NHS Scotland statistics show that 82.7 per cent of patients started treatment within 62 days between October to December - leaving nearly one in five waiting too long.
The Scottish Government target states that 95 per cent of patients with urgent referrals should be seen within 62 days, but the new figures show this ambition was missed for the sixth year in a row.
The figures also show a rise in the number of those waiting too long - up from 12.8 per cent in the same quarter in 2017 to 17.3 per cent last year. The 62 day standard was met by just one NHS Board - NHS Lanarkshire.
Overall, the statistics show that in 2018, a total of 2,436 people waited too long to begin cancer treatment.
Gregor McNie, Cancer Research UK's head of external affairs in Scotland, said the figures show "a service under huge strain with too many patients waiting too long."
He said: "Early diagnosis and prompt treatment delivers much better results for patients and yet cancer waiting time targets in Scotland are routinely missed. There are already shortages among key staff such as endoscopists and radiologists.
"If the NHS is to meet increasing demand, as well as diagnose as many patients as early as possible, the Scottish Government must plan to meet current and future need. New ways of organising services are needed, along with new investment which must reach the front line without delay."
However Health Secretary Jeane Freeman said the government's revised £6 million Endoscopy Action Plan will ensure new patients are seen within six weeks for key endoscopic tests, with the most urgent patients seen between two to three weeks.
She added: “This builds on our £850 million Waiting Times Improvement Plan, which aims to drive down waiting times across all specialities, including cancer diagnosis and treatment, outpatient appointments and day case procedures. We are committed to significantly improving the experience of patients waiting to be seen or treated.
“We’re treating more patients within both standards than the previous quarter and, once a decision to treat has been reached, patients in Scotland wait on average five days for treatment – a reduction from six days in the previous quarter for the 31 day standard.
“However, these figures show that some patients are waiting too long from urgent referral to treatment. I have been clear with health boards that cancer patients must continue to be prioritised."
Scottish Labour’s health spokesperson, Monica Lennon, said the public would be sceptical that the Scottish Government would deliver "rapid improvements", and highlighted Scotland's largest health board, NHS Greater Glasgow and Clyde, where only 77.4 per cent of cancer patients were treated within 62 days.
She said: “Cancer is Scotland’s biggest killer and early detection and treatment is crucial. This waiting time target exists to give people the best chance of survival and it is extremely concerning that it hasn’t been met once in the last six years.
“Behind these statistics are thousands of people enduring a worrying wait to begin treatment. Scottish Labour has long supported a two-week waiting time for cancer diagnosis to raise survival rates.
“The Health Secretary must set out in detail how she will urgently increase capacity in cancer detection and treatment to deliver the care that people need."
Scottish Liberal Democrat health spokesperson Alex Cole-Hamilton MSP branded the current waits for cancer treatment “outrageous”. He added: “A referral because cancer is suspected is an incredibly distressing time for patients and their families but under this SNP Government it is still not triggering urgent action.
“We need an end to long waits for cancer treatment and to force a new focus on making sure NHS staff and patients have the support and resources they need.”
And Scottish Conservative shadow health secretary Miles Briggs said: “Jeane Freeman continually refers to her Waiting Times Improvement Plan, but this isn’t much good for the people who are waiting too long now for potentially lifesaving treatment.
“The Scottish Conservatives have pledged to introduce a fast-track diagnostic service for cancer patients in order to significantly improve cancer waiting times in Scotland.”