While health secretary in 2012, Nicola Sturgeon pledged to increase the number of diagnoses of breast, colorectal and lung cancers in the first stage by 25 per cent by the end of 2015.
The target was missed – after the figure rose by just 8 per cent – but has fallen further in recent years.
Figures released by Public Health Scotland on Tuesday covering the whole of 2019 and 2020 show an increase of just 3.3 per cent from the baseline – which was made up of figures from 2010 and 2011.
But many cancer screening services were shuttered during the coronavirus pandemic, including for bowel cancer – which is included in the figures.
Over the past two years, 5,748 (24.1 per cent) people were diagnosed with the first stage of any of the three cancers – which make up a “significant proportion” of cases in Scotland – with 5,998 (25.2 per cent) diagnosed in the second stage.
While 4,133 (17.3 per cent) found they had cancer in stage three and 6,321 (26.5 per cent) in stage four, the stage of diagnosis could not be identified in 1,630 (6.8 per cent) cases.
Meanwhile, the total number of cancer diagnoses fell by 6.2 per cent between 2018/19 and 2019/20.
Scottish Liberal Democrats leader Alex Cole-Hamilton said: “These figures only cover the first few months of the pandemic, yet we are seeing significant falls in the number of patients diagnosed with cancer.
“We know that early diagnosis and treatment is crucial to patients’ chances of survival so this raises enormous red flags for what the full 2020 figures will show.
“The Scottish Government need to undertake rapid work to assess the scale of the challenge. Then we need fresh funds and resources, coupled with a timeline for meeting cancer waiting times targets, to ensure that the knock-on effects of the pandemic do not do even more damage to people’s health.”
Scottish Labour deputy leader Jackie Baillie warned there was a “looming cancer catastrophe” in Scotland.
“Early diagnosis can be the difference between life and death – but things are the worst they’ve been in years,” she said.
“The real risk is that we are just seeing the tip of the iceberg here.
“Right now we should be pulling out every stop to get back on track – but instead health boards are being forced to cancel cancer operations.
“The SNP are playing fast and loose with people’s lives.
“They need to stop wasting time and act now to put in place the cancer catch-up plan we have needed for months.”
The statistics came as other Public Health Scotland figures released on Tuesday showed the mortality rates from all combined cancers are 66 per cent higher in the most deprived areas than the most affluent.
Those in the poorest areas are also 28 per cent more likely to be diagnosed with cancer than their rich counterparts.
The figures, from 2019, show 16,366 people died from all types of cancer, up from 16,153 in 2018.