More than a quarter of cancers in Northern Ireland are being diagnosed in hospital emergency departments, according to Cancer Research UK.
The study, published in The Lancet Oncology, was supported by NI Cancer Registry at Queen's University Belfast.
It looked at 857,068 cases diagnosed between 2012 and 2017 in six countries including Australia, Denmark and the UK.
Clare Crossey, 35, from Lurgan was diagnosed with acute myeloid leukaemia in February 2018 after being admitted to hospital as an emergency.
The 35-year-old mother-of-two, who is a domiciliary care assistant, suddenly became very unwell with symptoms including tiredness and bruising.
She told BBC News NI she had contacted her local health centre, where a GP told her she was being overly anxious.
Ms Crossey said she had panicked, fearing she may have leukaemia after looking up her symptoms on the internet.
"I had a feeling that things weren't right," she said.
"The doctor did not agree with my suspicions as they passed me the number of the Samaritans helpline, a prescription for beta blockers and told me to wait a week for blood tests."
She said: "I went to Craigavon's A&E, they did blood tests and within hours a consultant broke the news to me that I might have leukaemia."
The medical team told her that had she waited any longer to come to the emergency department, she could have died, said Ms Crossley.
Barbara Roulston, from Cancer Research UK, said the study confirmed too many people were only being diagnosed with cancer once their health had deteriorated to a point when they needed to go to their emergency department.
"We need to reduce the number of cancer diagnoses that are happening in this way," she said.
"That means renewed focus on early diagnosis and prevention through things like better awareness of symptoms, better uptake of screening programs and the way to do that is to get funding for the cancer strategy which was published recently.
"If we don't, the risk is that we will start to see cancer survival going backwards."
Source: BBC News, 7 April 222