NHS statisticians have recorded the most sizeable drop in the percentage of patients treated within 62 days of urgent referral with the suspicion of cancer since the target was set in 2012.
There has also been a slight drop in the percentage of patients waiting 31 days from the decision to treat, although the NHS remains above target with only three boards failing to reach the required 95%.
Between January and March this year, 91.5% of patients started treatment within 62 days of urgent referral with suspicion of cancer, according to the NHS Information Services Division (ISD).
This compares to 94.6% in the period October to December 2013.
Some 96.2% of patients started treatment within 31 days of decision to treat. This compares to 97.9% in the period October to December last year.
Only five out of 14 NHS boards met the 62-day target - NHS Ayrshire and Arran, NHS Borders, NHS Dumfries and Galloway, NHS Lanarkshire and NHS Orkney.
This compares to nine out of 14 in the period October to December 2013.
Twelve out of 15 NHS boards met the 31-day target - with only NHS Grampian, NHS Highland and NHS Greater Glasgow and Clyde falling below standard.
This compares to all boards meeting the target in October to December 2013.
Some 97% of the patients that were urgently referred with a suspicion of cancer from the breast screening programme, 100% from the cervical screening programme and 85.5% from the colorectal screening programme were seen within 62 days of referral.
The Scottish Government has announced an additional £2.5 million investment to help health boards meet cancer waiting times in light of today's figures.
The money will help health boards to meet the 62-day cancer standard by building diagnostic and treatment capacity.
Health Secretary Alex Neil said: "A cancer diagnosis is devastating news. That's why I welcome that the average length of time a patient waits to start their cancer treatment in Scotland is just six days as we know that the sooner a patient starts treatment the better their chances of survival.
"We are also consistently reaching the demanding 31-day target for treatment despite the fact our NHS is treating more people than ever before and coping with the demands of an ageing population.
"We have progressively tightened Scotland's NHS targets for cancer care to benefit patients and I can confirm today we are investing a further £2.5 million this year on top of the £9 million invested over the last three years to improve cancer services.
"But we must do more - in particular on our 62-day standard. While this has increased from 84.5 per cent of patients starting treatment within this target in 2007, we remain fully committed to once again reaching our standard of 95 per cent.
"We had already identified specific boards experiencing dips in performance and I sent in a support team to identify where urgent action is needed.
"These figures cover the period before this team got to work, so I am confident boards will already be delivering changes for patients.
"These local solutions include the recruitment of additional frontline staff, a £10.8 million funding boost for new theatres and a further £478,000 investment in endoscopy services in NHS Grampian.
"We anticipate that the measures being taken by health boards will bring about significant improvements in performance right across Scotland."
Scottish Conservative health spokesman Jackson Carlaw said: "The Scottish Government can no longer keep offering up lame excuses as to why two-thirds of health boards are failing to hit such critical targets.
"What on earth have ministers been doing over the past year to allow this disgraceful situation to take hold?
"These aren't patients sent on a whim for a check-up - we are talking about those deemed to need 'urgent' surgery on account of them probably having cancer.
"We all know how lethal this disease can be yet hundreds of ill people are being forced to wait more than two months for potentially lifesaving treatment to begin.
"No doubt the health secretary will appear on our screens and airwaves offering yet another feeble explanation as to why we're doing so badly on this.
"But it's not good enough, this is a Scottish Government that has forgotten its priorities, and cancer patients are paying the price."
Labour health spokesman Neil Findlay, said: "It's bitterly disappointing that once again these crucial targets are not being met.
"A cancer diagnosis is one of the worst things a person and their family can go through and it's appalling that the average start time for treatment for Scots diagnosed with cancer is 39 days.
"Nine out of the 14 health boards are missing the 62-day target and that is simply not good enough.
"Additional funding is welcome but I am hugely concerned that the £2.5 million announced, by the Health Secretary Alex Neil, is not nearly enough to address this issue.
"In March Alex Neil said that support squads would be sent in to improve performance in hospitals treating cancer patients, yet the latest figures are actually worse than before.
"He must do more than give token gestures; the reality is that these targets are about real people and his failure to act is causing huge distress to thousands of people across Scotland. More must be done."