More than two in five people who developed suspected cancer symptoms during the UK's first lockdown did not seek medical help, research suggests.
"Stay at home" restrictions have helped to protect the NHS from being overwhelmed as the pandemic unfolds.
Doctors and officials alike have repeatedly stressed the health service is open for business, however, after reports emerged critically-ill people have been reluctant to go to hospital over fears of catching the coronavirus.
To better understand the scope of the problem, scientists from Cardiff University surveyed more than 7,500 people.
Two in five (40%) claimed to have experienced at least one potential cancer symptom between March and August 2020, during which time coronavirus restrictions ebbed and flowed in severity.
Of these participants, a further two in five (44%) did not contact their GP over the symptoms, even when there was a serious red flag, like coughing up blood or an unexplained lump.
One in two people born after 1960 in the UK will statistically develop cancer at some point in their life. The earlier the disease is diagnosed, the faster the patient can be treated, boosting their survival hopes.
"From the early data we collected after the first lockdown we can see the COVID-19 [the disease caused by the coronavirus] pandemic has affected public attitudes to seeking help for signs and symptoms of cancer which may translate into delayed referrals, missed tests and later-stage diagnosis," said lead investigator Professor Kate Brain.
"This suggests the government's message to 'stay home, protect the NHS, save lives', which was intended to control the spread of COVID-19, also sent a strong message to the public that cancer can wait.
"While we recognise measures to control the spread of COVID-19 are essential, we also need to send a strong and clear message that cancer cannot wait, that people should contact their GP with any unusual or persistent symptoms, and that NHS services are open safely."
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The study's participants were asked about their experience of 15 potential cancer symptoms during that five-month period.
Results reveal just under a third (30%) of those who coughed up blood did not seek medical attention, while 41% ignored an unexplained lump or swelling.
More than half (58%) of those who experienced a change to a mole's appearance, a sign of skin cancer, did not have it checked over.
One respondent, a 46-year-old woman, said: "I would have stayed away and just dealt with it, rather than perhaps going to see a doctor at an early stage."
Professor Brain, a psychologist, worries the public "put their health concerns on hold to protect the NHS".
The results further show more than one in 10 (15%) of the participants worried about wasting a medic's time.
A similar proportion (12%) were concerned they may put an additional strain on the NHS or be seen to be making a fuss.
"I'm of the mindset that says, 'if it's not sort of life-threatening then, you know, it can wait'," said a 63-year-old female respondent.
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The results also reveal one in 10 (10%) of the participants had "difficulty accessing healthcare services".
A wheelchair-bound respondent struggled with her GP surgery's newfound one-way system.
"You see I have to go round the back of the blooming doctors and that was a nightmare, because it was a little tiny path," said the woman, 44. "My husband had to make sure I didn't fall out of the wheelchair."
Just under one in 10 (9%) also worried they would catch the coronavirus if they sought medical attention.
"I needed stitches in my knee, because I fell," said a 44-year-old woman.
"My husband used butterfly stitches and done it that way. I wouldn't go [to hospital] because of COVID, because I was too frightened."
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Perhaps reassuringly, around two-thirds of the respondents felt they would be safe from the coronavirus if they had to see their GP (68%) or go to hospital (61%).
Nearly three-quarters (72%), however, were concerned the pandemic would delay cancer tests.
"Catching cancer at an early stage gives the best possible chance of surviving the disease so we're extremely concerned people have put off seeking help for cancer symptoms, even if this was for the best of intentions," said Michelle Mitchell, chief executive of Cancer Research UK.
"Worryingly we don't yet know what the pandemic's long-term impact on cancer stage and survival will be, so it's vital people don't delay contacting their GP if they notice any unusual changes to their body.
"NHS staff have worked incredibly hard to manage the increased strain COVID-19 has put on an already stretched system, but the government must protect cancer services if we're to avoid the real possibility cancer survival could go backwards for the first time in decades."
Cancer survival has doubled in the UK over the past 40 years, with one in two patients living at least 10 years post-diagnosis.
Cancer Research UK aims to accelerate the 10-year survival rate to three in four patients by 2034.
The study's results make up part of a policy briefing paper calling for co-ordinated campaigns across the UK, which will highlight the NHS is open and safe for anyone with unusual or persistent symptoms.
Clear information should encourage the public to contact their doctor promptly, as well as explaining the changes a patient should expect to their GP practice's procedures, according to the policy paper.
Worries around NHS capacity and infection control must also be alleviated, it adds.
"GPs across the UK are doing everything we can to ensure people get the care they need so if you've noticed an unusual or persistent symptom, tell your doctor, we do want to hear from you," said Dr Neil Smith, Cancer Research UK's GP adviser.
"In most cases it won't be cancer, but if it is, catching it early gives the best chance of successful treatment.
"For those who've been unable to get through to your doctor’s surgery, although it might be frustrating, I would encourage you to keep trying.
"GPs like me are still here to help you."