As of June 30 this year, official NHS statistics showed 87,482 patients needed to have one of eight key diagnostic tests and investigations - with 18,644 of them having been waiting six weeks or more.
That compares to the 4,750 patients who had to wait longer than the Scottish Government’s target in June 2016 - an increase of 292.5%.
Cancer Research UK branded the increasing number of people waiting for tests as “deeply concerning”, with Labour blaming the NHS “staffing crisis” for the rise.
The figures were released at the same time as data showed the number of people waiting more than 12 weeks for inpatient or day hospital treatment reachers 18,338 in the three months to the end of June - the highest total ever since the Scottish Government’s Treatment Time Guarantee was introduced in October 2012.
NHS statistics also revealed the 18-week Referral To Treatment time standard has not been met since June 2014.
Longer waits for an endoscopy - where a tiny camera on a long, thin, flexiblee tube is passed into the body - were blamed for the poor performance on waiting times for diagnostic tests, with only 56.6% of people waiting for one of these having the test within six weeks in June 2018, compared to 64.3% at the same time last year.
Gregor McNie, Cancer Research UK’s head of external affairs, said: “These statistics suggest that the NHS in Scotland does not have enough staff to be as effective as possible in diagnosing cancer.
“This situation is deeply concerning, particularly as demand for tests is only going to grow due to an aging population and efforts to diagnose more people at an early stage.
“It’s vital patients receive the right tests and results in good time. It’s crucial there are enough imaging, endoscopy and pathology staff working to deliver tests.”
He added an endoscopy action plan, brought in by the Scottish Government, was a “good start” but stressed that “much more needs to be done to tackle all shortages, both in the near future and the long term”.
Labour health spokesman Anas Sarwar also demanded action, saying: “Performance for key clinical tests simply have to improve - early detection saves lives.
“These standards are in place to ensure that people with potentially serious conditions get the benefit of early detection and have the best possible chance of a full recovery.”
He added: “Health Secretary Jeane Freeman has inherited a health service facing a staffing crisis - solving that is vital to reducing the pressure on services and delivering the care that patients need.”
Meanwhile over the period April to June 2018 just under three quarters (74.6%) of those waiting for hospital treatment, as either an inpatient or day patient, waited less than the 12 week Treatment Time Guarantee for this - down from 81.2% in the same quarter last year.
In NHS Forth Valley only 56.1% people were treated within this time, according to the latest figures.
Other statistics showed that in June 2018 only five of the 15 NHS boards who submitted valid data met the 18 weeks Referral To Treatment standard - which sets out how long patients should have to wait after being referred for treatment by their GP.
The target sets out for 90% of patients to be treated within this time, but this was last achieved in June 2014.
In June 2018, 82.8% of patients across Scotland were reported as being seen within 18 weeks, up from 80.9% in April and 82.6% in May.
Despite this the Scottish Government said patient satisfaction was at a record high, with the latest survey of hospital inpatients showing 86% described their care as positive, while 91% positively rated the staff who had looked after them.
Ms Freeman said: “NHS investment and staffing are at historically high levels, and the record high inpatient satisfaction rates published today are a testament to the hard work of our frontline NHS staff.”
“Meeting the challenge of improving performance and reducing waits requires the twin approach of investment and reform. That’s why we recently allocated an additional £6 million to reduce waiting times for endoscopies, with a focus on the most urgent patients, including those with suspected cancer.
“That is seeing immediate steps to cut the number of people across Scotland waiting for diagnostic testing, with health boards working towards reducing the number of patients waiting over six weeks by 5,000 by the end December 2018.
“This investment followed a package of measures - including £50 million extra funding - to reduce long waits for treatment. We will continue to work with boards to ensure that this additional funding delivers the improvement needed.”