BY the time Donald Marshall was diagnosed with kidney cancer, the tumour was so large it was pushing against his lungs and leaving him short of breath.

Even then, it was only picked up by chance when a chest X-ray happened to catch the edge of the mass. At the time, Mr Marshall had been complaining of a persistent cough for years which was initially dismissed as asthma during a GP check-up in 2010.

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A combination of the breakdown of his marriage and subsequent house moves also saw his sky-rocketing blood pressure blamed on stress.

"I went for the respiratory clinic in early summer 2012 and they did what they call spirometry tests where you blow into a machine to check your lung function," said Mr Marshall, now 58. "They found there wasn't really anything wrong, except that I couldn't seem to breathe in fully.

"It was a registrar I was seeing and at the end she decided she'd have a word with her boss, who I presume was the consultant, and came back to say they'd send me for a chest X-ray.

"When this X-ray came back that they noticed there was an abnormality in the kidney, which just happened to be in the picture. Had the X-ray not gone quite so low down they'd probably never have found it. It was caught completely by chance.

"They talk about it in cancer circles as an 'incidental diagnosis': they were searching for something else and came across this."

Mr Marshall, a professional gardener who lives in Knightswood, Glasgow, is typical of the experiences of kidney cancer patients highlighted in a new survey by Kidney Cancer UK.

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The charity found that 43% of patients only learned that that had the disease when they were undergoing tests or scans for another, unrelated condition.

Nearly half (47%) were not diagnosed until the cancer was more advanced - stage 3 or 4 - when it is more difficult to treat, and 45% said they had initially being misdiagnosed with less serious ailments such as a urine infection or kidney stones.

The charity stressed that this is not a failure by medics, but a lack of effective diagnostic tools.

It said: "We have known for some time that kidney cancer is difficult to diagnose. A simple blood test to detect it needs to be developed, but until such a test is available, the need for evidence-based diagnostic tools is paramount."

It comes as the latest figures for Scotland reveal that the number of people dying from cancer has continued to increase, largely due to more people falling ill as the population becomes more elderly.

However, mortality rates have declined 10% over the decade, indicating that more patients are surviving cancer.

This pattern is also true for kidney cancer, which claimed 387 lives in Scotland in 2017 compared to 366 in 2007.

By comparison, the mortality rate - which is adjusted to take into account changes in the population age - shows that the risk of dying from kidney cancer in Scotland has fallen from nine per 100,000 people in 2007, to 7.8 per 100,000 last year.

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Mr Marshall, who has since remarried, is one of the lucky ones. His diseased kidney was removed and scans did not show any evidence that the cancer had spread.

However, he was still rated at a high risk of relapse and doctors gave him only a 30% chance of getting past five years still being all-clear. So far, he has defied the odds.

He said: "They have a scoring system which rates the risk of the cancer returning on a scale of one to eight, eight being the highest, and I was a seven," said Mr Marshall. "The tumour had punctured one of my veins so the chances are that there are tumour cells floating around in my bloodstream. If one of them decides to stop off and start growing then it could come back again. But so far it hasn't.

"I've known a few folk during the past few years, younger than me, who've passed away. I still keep in touch with their families and partners, but it's quite a sobering thought when you see that."

Mr Marshall, who now supports other patients through Kidney Cancer UK's 'buddy' system, urged people not to ignore persistent symptoms.

He said: "I always talk about 'the cough' - the 'cancer cough'. Your tumour gives off toxins which can cause irritation in the lungs which makes you cough. It was a very severe cough - it woke me up in the night, I was choking and coughing up phlegm.

"Not blood or anything, but it was like having a heavy cold all the time for five years. And it just kept getting worse.

"But strangely enough, a few weeks after the operation, no cough. When I look back all my symptoms were there: I had high blood pressure, I had this cough, but it's just a case of being made aware of them.

"I'm not criticising the GPs - they tried all sorts of things - but I suppose there's a tendency to try to rule everything else out before you check for cancer, and maybe cancer should just be a bit higher up the list. Why not rule it out first?"

Other common kidney cancer symptoms include fatigue, blood in urine, back or side pain, weight loss or night sweats.

Gregor McNie, spokesman for Cancer Research UK in Scotland, said: “Thanks to advances in research, new and better treatments are coming on stream which will help more people survive.

"Too many people are diagnosed when their cancer has already spread and is harder to treat. If we can diagnose more cancers earlier, it’s likely more people will survive. To do this, we need to make sure that people with suspected cancer are offered the right tests."