Figures for the first quarter of 2022 show performance against the 62-day treatment target fell to 76.9%, down from 79.1% in the previous quarter.
The standard has not been met since the end of 2012.
The Scottish Government says meeting the target “remains challenging” and more must be done to improve waiting times.
Statistics from Public Health Scotland showed performance against another target – the 31-day standard from decision to treat to first cancer treatment – was met with 96.3% of patients being seen within this timeframe.
The 62-day standard is based on the time from urgent suspicion of cancer referral to first cancer treatment.
Janice Preston, of Macmillan Cancer Support in Scotland, said: “Any delay in receiving a cancer diagnosis and starting treatment causes a huge amount of worry and distress.
“We know that many people have complex emotions associated with what might have happened had they been diagnosed or treated sooner.
“Early diagnosis and timely treatment provides the best possible outcomes for people with cancer.
“These latest figures show a struggling system which cannot meet demand – despite the hard work of staff – and this must be addressed urgently.
“Improving access to psychological care and emotional support must also be a priority for cancer services, to deal with the effects of the pandemic on patients and their families, as well as helping individuals cope with the consequences of cancer and its treatment.”
Opposition parties criticised the Government’s record on cancer waiting times.
Conservative health spokesman Dr Sandesh Gulhane said: “These startling figures should be a source of shame for Humza Yousaf and the SNP.
“It’s completely unacceptable that almost a quarter of patients are waiting more than two months to begin treatment following an urgent referral.
“When a patient comes to see me with signs of cancer, I act quickly because time is vital to their survival – yet these figures highlight a truly terrifying reality when it comes to cancer diagnosis in Scotland.”
Scottish Labour’s Jackie Baillie said: “These catastrophic figures must be a wake-up call for the SNP Government, who have so far been posted missing as cancer services fall into chaos.
“Nicola Sturgeon promised to focus on recovery, but as cancer waiting times hit their worst point on record she is distracted by her constitutional obsession.
“The SNP have ignored warning after warning about the mounting pressure on cancer services, and there is no doubt that this shameful negligence will cost lives.”
A Scottish Government spokesman insisted it “must do more”.
He said: “The 31-day standard has been consistently met throughout the Covid-19 pandemic with a median wait of four days.
“However, the 62-day standard remains challenging for this quarter with a median wait of 47 days and we must do more.
“We are investing in ways to support cancer waiting times improvements, including up-skilling nurses, investing in diagnostic tests focussing on the most challenging pathways to reduce backlogs.”