Cancer patients in Helensburgh and Lomond are waiting longer than they should for treatment.
Anyone suspected of suffering from the disease is expected to be seen by experts within a maximum of 62 days.
But Helensburgh's MSP, Jackie Baillie, has revealed that the 62-day standard set by the Scottish Government has only been met by two health authorities - NHS Borders and NHS Lanarkshire - since 2012.
Both boards met this target between July and September 2018.
In NHS Greater Glasgow and Clyde, almost 25 per cent of patients were left waiting for treatment for longer than 62 days between July and September 2018, an increase on the previous quarter.
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Ms Baillie said: "Patients who are suspected of having cancer are being expected to wait longer and longer for the urgent treatment that they need.
"In NHS Greater Glasgow and Clyde more than 25 per cent of patients are not receiving treatment within the 62-day target time.
"Everyone knows that early diagnosis and early treatment means that patients are more likely to get successful outcomes, so these delays could threaten lives.
"It is clear that health boards across Scotland are struggling with reduced resources and staff and patients are being let down.
"Our NHS urgently requires increased resources to ensure that patients are given the support and treatment that they desperately need."
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Health Secretary Jeane Freeman said: "It's welcome that 95 per cent of patients in Scotland were once again treated within the 31 day standard, and that once a decision to treat has been made patients wait on average six days for treatment.
"However, despite an increase of 31.6 per cent (738) of patients being treated within the 62 day referral standard than ten years ago, performance against this target is simply not good enough.
“Recently I launched the Waiting Times Improvement Plan which, backed by an investment of £850 million, will drive down waiting times for cancer diagnosis and treatment, outpatient appointments and day case procedures.
“We are committed to significantly improving the experience of patients waiting to be seen or treated.
"I have been clear with health boards that achieving this will require a focused, intense programme of work that accelerates action that is already underway.”
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