Public Health Scotland (PHS) data showed just 74.7 per cent of patients started treatment within the official 62-day standard across July and September.
It is a record low compared to the 79.3 per cent in the previous quarter and 83.7 per cent at the end of December 2019.
No health boards met the standard of 95 per cent in this quarter – and nationally it has not been achieved since the end of 2012.
However, 4,161 eligible patients were referred for the 62-day standard, which is an increase of 2.2 per cent from the previous quarter and an increase of 11.8 per cent from the quarter ending December 2019.
The 62-day standard is based on the time from urgent suspicions of cancer referral to first cancer treatment.
Statistics also showed performance against another target – the 31-day standard from decision to treat to first cancer treatment – fell just short, with 94.3 per cent of patients seen compared to 95.5 per cent in the previous quarter and 96.5 per cent in the final quarter of 2019.
The target was missed by NHS Grampian, Greater Glasgow and Clyde, Highland, Lanarkshire and Lothian.
Janice Preston, head of strategic partnerships for MacMillan Cancer Support in Scotland, said: “Cancer waiting times have been getting worse for years, and today’s figures show the worrying trend continues right across the country, even before the added pressure of winter is factored in.”
It is understood health boards are reporting workforce issues as one of the main reasons why the targets were missed.
Ms Preston continued: “We know there’s not a simple fix, but the simple fact is that people with cancer in Scotland need and deserve a system that can treat them faster.
“Despite today’s statistics, we want to make sure everyone hears a very clear message – please, if you have worrying or unexplained symptoms, get them checked out by your GP practice.”
Scottish Labour health spokeswoman Jackie Baillie said: “This is a full-blown disaster and there’s no doubt it will cost lives. NHS staff are exhausted and demoralised, and cancer patients are being left to deteriorate.
“The SNP have ignored warning after warning about the ticking time bomb of cancer cases they let pile up during the pandemic, and now we are seeing the consequences. We need urgent action if we are going to stand a chance of undoing the damage done by this dangerous negligence.”
Scottish Tory health spokesman Dr Sandesh Gulhane expressed his shock at the figures, saying: “These figures are truly terrifying. It is disgraceful that over a quarter of cancer patients are not starting treatment within two months.
“That will have a potentially devastating impact on their chances of survival. All of this is happening on Humza Yousaf’s watch, with cancer waiting times worsening every quarter since he became health secretary.”
Mr Yousaf said the Covid-19 pandemic had placed significant strain on the NHS, including cancer services. He said: “Despite those pressures, more patients were treated on both 62-day and 31-day cancer pathways this quarter compared to the previous quarter, the same time last year (Q3 2021) and the last full quarter pre-pandemic (Q4 2019).
“The median wait for treatment on the 31-day pathway remains at four days, with over nine out of ten people being treated within the 31-day target.
“We’re investing £40 million over five years to support cancer services and improve waiting times, with a focus on urology, colorectal and breast with £10 million released to boards targeted at these most challenged pathways.
“We are committed to finding cancer as early as possible which is why we are expanding Rapid Cancer Diagnostic Services across Scotland and yesterday published Scotland’s first optimal cancer diagnostic pathway for lung cancer, alongside £3m investment.”