It was the end of GCSEs, and Amy Clark was celebrating with friends when she tumbled off a fence she had been sitting on and landed badly on her back.

The 16-year-old from Bristol was fine at first, but over the next two years she suffered intermittent back pain, which she put down to the fall.

After finishing school altogether, Amy decided it was time to get it checked out, booking an appointment with a back specialist, who referred her for a scan. The results showed her back was normal – but they also revealed something far more worrying: a suspicious speck on her right lung.

‘I was whisked off to see the respiratory consultant,’ Amy recalls, ‘who told me they usually only see this sort of thing in long-term smokers and alcoholics – not in someone my age.’

Doctors initially decided to monitor the lesion to see if it would resolve on its own. But eight months later, a follow-up scan and biopsy brought devastating news.

Amy had stage four lung cancer. It had already spread from her right lung to her lymph nodes and back ribs, making it incurable. She was just one month shy of her 21st birthday.

‘It was a massive shock – I’d had no symptoms whatsoever. Cancer had never even popped into my head,’ she said. ‘I had always thought that lung cancer was something that long-term smokers got – and I’d never touched a cigarette.

‘I was concerned about my family and how they would take it. But I just couldn’t stop thinking – how has this happened?’

Amy Clark was diagnosed with stage four lung cancer just one month before her 21st birthday

Jules Fielder was 37 when she noticed a lump in her neck, with this leading to her diagnosis

Jules says she went to her doctor multiple times about pain in her back and elbow – only to be diagnosed with sciatica and tennis elbow

While shocking, Amy’s story is not as unique as it may seem.

She is one of tens of thousands of young people to develop lung cancer despite having never smoked – long thought to be the main trigger – and no genetic predisposition to the disease. It’s a phenomenon that has left scientists both baffled and concerned.

As smoking rates and related cancers decline, cases such as these are rising. Unusually, it’s women who are most affected, making up nearly seven in ten cases.

Today, around 20 per cent of lung cancer diagnoses are in people who’ve never smoked – and studies suggest that figure is set to rise. If so-called never-smoker lung cancer were a disease of its own, it would rank as the 8th leading cause of cancer death in the UK and 7th globally.

Now doctors believe that they may have found an explanation: air pollution. ‘It’s well established that there’s a link between air pollution and lung cancer, but we think it may be especially important in patients who have never smoked,’ explained Dr William Hill, a researcher at the Francis Crick Institute, London, and part of a team currently investigating the phenomenon. ‘Our research found that these tiny solid particles in the air are inhaled and can cause an inflammatory response in the lungs, which can promote the development of cancer. And we have also found a link between high levels of these particles and increased rates of certain types of lung cancer in people who have never smoked.’

With nearly 48,000 people diagnosed each year, lung cancer remains the third most common cancer in the UK – and the leading cause of cancer-related death.

Today, about 85 per cent of lung cancer cases are still caused by smoking, when chemicals damage lung cells and trigger cancer-causing DNA mutations. But that percentage is falling.

It’s a trend consultant oncologist Dr Alexandros Georgiou began noticing at his clinic at Guy’s and St Thomas’ Hospital in south-east London – and one he decided to investigate.

What Dr Georgiou’s team discovered was that the proportion of patients without a history of smoking was increasing year by year. Just five per cent had never smoked in 2010. By 2021 it was 14 per cent.

Another of the study’s findings was similarly concerning: of these never-smoker lung cancer sufferers, the vast majority were female – at 68 per cent. And these patients were younger, on average, than those with smoking-related lung cancers.

‘This shifting demographic is partly due to the increasing prevalence of non-smokers in society, meaning the pool of non-smokers who could potentially get lung cancer is getting bigger,’ said Dr Georgiou. ‘But I don’t think that fully explains the change that we’re seeing.’

The difficulty with lung cancer in non-smokers, explains Professor Matt Evison, associate medical director for the Cancer Alliance, is that by the time it is caught, it tends to have already spread to other parts of the body.

‘It’s a difficult diagnosis because the common symptoms of lung cancer can have many other explanations,’ he says. ‘A cough, breathlessness, chest or upper back pain can all be put down to other, much more likely causes.

‘Lung cancer will rarely be the diagnosis for a patient who comes in with a cough.’

The other difficulty is that symptoms of lung cancer in non-smokers can be different to those typically associated with smoking-related lung cancer, and tend to appear later.

‘In never-smokers, lung cancer is more likely to present as a dry cough than smoking-related cancer, which can cause patients to cough up blood,’ says consultant clinical oncologist Dr James Wilson.

‘Symptoms can also be more generalised and less specific to the lungs – like weight loss or fatigue. And as it progresses, it’s more likely to present with breathlessness and pain in various areas of the body than in cancers caused by smoking.

‘This is both because patients tend to be young and fit, and also because the type of cancer they tend to get – called adenocarcinoma – usually grow in the periphery of the lung. Cancer from smoking, meanwhile, causes tumours around the central airway that are more likely to bleed and cause patients to cough up blood or phlegm.’

As a result, patients and medics alike are too keen to dismiss symptoms, says Prof Evison. ‘In medicine, we might have an idea in our head of the type of person who gets lung cancer,’ he explains.

‘Two people who come in with the same symptoms may have lung cancer put in very different places on the list of likely causes.’

This means around 90 per cent of never-smokers with lung cancer are diagnosed only when the disease is at an advanced stage and incurable.

This was the experience of Jules Fielder, who was just 37 when she was diagnosed with incurable lung cancer – having never smoked. ‘We’d just got back from camping in the Isle of Wight and I was putting jewellery on in the bathroom when I noticed a lump at the base of my neck, by my collarbone,’ says the mother-of-one.

After a flurry of tests, Jules got a phone call on Christmas Eve from her doctor: she had lung cancer that had spread to her lymph nodes as well as her spine and pelvis.

‘It was a hard hit,’ she says. ‘Especially being told that it was incurable – to know I can’t do anything about it.’

Jules says she went to her doctor multiple times about pain in her back and elbow in the months prior – only to be diagnosed with sciatica and tennis elbow. ‘It was like putting a jigsaw together piece by piece. These were all signs that could have been picked up,’ she adds.

Now experts say breakthrough findings pinpointing the cause of these cancers could help women like Jules and Amy in the future.

Numerous studies have linked air pollution to lung cancer, with a paper as early as 1950 blaming both outdoor pollutants and fossil fuels, but scientists couldn’t explain exactly how – until now.

One major risk factor for lung cancer in non-smokers is a mutation in the EGFR gene, which controls how cells grow and divide. When this mutates it can trigger uncontrolled growth and tumour formation – and it’s found in nearly 20 per cent of adenocarcinomas in non-smoking women.

These mutations aren’t usually inherited, and lung cells carrying them typically lie dormant and harmless. However, Dr Hill says: ‘We have found that air pollution seems to wake up these cells.’

While air pollution has decreased over the past half century, it was only in the last two decades that the UK saw most significant reduction in indoor wood burning, coal burning and vehicle exhaust within cities and towns. And as the gene mutations can occur as long as 30 years before the cancer develops, the number of cases is expected to continue to rise.

Experts say the good news is that if air pollution continues to fall, these cancer rates could decline too.

However, others suggest hormones could play a role.

‘Some have hypothesised that the increased risk of lung cancer in women who have never smoked could be hormonal – the oestrogen could have a role,’ said Dr Robert Hynds, a senior research fellow in biology and cancer development at University College London. ‘Others speculate that it could be due to women’s higher susceptibility to autoimmune diseases, which causes inflammation in the body, potentially increasing cancer risk.

‘It’s not as simple as with tobacco smoking, which we know definitively causes lung cancer. We believe that air pollution – both indoor and outdoor – promotes lung cancer in some way, but it’s not yet as well understood and studied.’

The recent findings bring researchers one step closer to identifying high-risk individuals and preventing the disease, says Dr Hill.

Treatments for gene-mutated lung cancers are already more advanced than for many other types. Instead of gruelling chemotherapy, patients are often given targeted drugs called tyrosine kinase inhibitors. Taken daily, these tablets block the faulty gene’s activity, halting tumour growth and keeping the cancer at bay – often for years.

For Amy, the targeted therapy has allowed her to more or less live her life as normal since her diagnosis. Now 26, she’s still working, loves to walk, hike and hang out with her friends, and has even been to Glastonbury five times.

 I thought it was long Covid – it wasn’t

In 2020, Mel Erwin, then 51, initially suspected her breathlessness was caused by long Covid

When she began suffering breathlessness and fatigue, in 2020, Mel Erwin, then 51, assumed it was long Covid – the lingering aftermath of a nasty bout of the virus she’d caught months earlier.

When she eventually went to her GP, she was sent for a chest X-ray and blood tests – and received a phone call the same afternoon.

‘My bloods were fine but they’d found a mass in my left lung,’ Mel recalls. ‘I asked if it was Covid or cancer – and he said it could be cancer.’

The day after her 52nd birthday, Mel had half of her left lung removed. But two years later, a scan showed new lesions across both her lungs that were too small to biopsy. 

After another two years of monitoring, Mel was then diagnosed with advanced, incurable lung cancer.

Now she’s taking a targeted therapy, called Osimertinib, to inhibit the gene mutation that is causing the cancer to grow and spread. ‘It’s allowing me to live well, and I plan on living for decades,’ said Mel, who’s training for Sir Chris Hoy’s fundraising charity bike ride Tour de 4. 

In the future, though, she hopes more people will be aware that it’s possible to get lung cancer without a history of smoking – and to push if they have any symptoms of the disease.

‘Don’t worry about making a nuisance of yourself – be a nuisance if something is wrong,’ she urged.