A breast cancer survivor and a man whose wife died from the disease have reacted angrily to revelations that an NHS computer error led to 450,000 people missing screening tests.
Patricia Minchin said her "traumatic journey" could have been "avoided".
Brian Gough, whose wife Trixie died in 2015, said she might have survived if her cancer had been diagnosed earlier.
A think tank has questioned why the error, for which the health secretary has apologised, was not spotted sooner.
Women aged between 50 and 70 are supposed to be invited for a mammogram every three years.
But about 450,000 women in England aged 68-71 failed to get invitations since 2009 because of a computer error, Health Secretary Jeremy Hunt told the Commons.
He said the mistake could have shortened the lives of up to 270 women.
Ms Minchin, a former nurse, told the BBC she believed she was one of those who should have got an invitation for a screening, but didn't.
She was tested in 2009 when she was 67 but was not called back for a second examination.
In 2015 she discovered three lumps in her breast, two of which "were deep" and "had obviously been growing for some time".
Mrs Minchin underwent chemotherapy and radiotherapy in what she called a "traumatic journey".
She said: "You can never say it could have been prevented but I really think if I had had a mammogram when I was 70, (the cancer) may have been picked up."
Brian Gough, 77, said he was shocked by Mr Hunt's revelation.
His wife Trixie was diagnosed with breast cancer in 2010, a year after she should have had a scan.
The cancer was treated but returned and his wife died three days after Christmas 2015 aged 76.
Mr Gough, from Norfolk, said: "She didn't know anything about it until a year too late."
What to do if you're affected
- Call the breast screening helpline number 0800 169 2692
- Go the NHS Choices website for more information
- You should receive a letter by the end of May
He said "maybe just maybe" Mrs Gough – to whom he had been married to for 56 years – would have survived if treatment for the first cancer had started earlier.
The widower said: "I can't express how sad it is.
"I know we can't be certain it would have picked up her cancer as it may not have developed or that she would have survived, but it is possible."
Early diagnosis is "absolutely essential" according to Baroness Delyth Morgan, chief executive of Breast Cancer Now.
She said: "I feel extremely sad for the women affected by this colossal administrative disaster.
"It's hugely significant, we have to be concerned about confidence in the screening service."
Meanwhile, the Institute for Public Policy Research (IPPR) has questioned why a fall in the number of women getting screened did not raise any alarms.
In a recent report on the NHS, the IPPR said the number of women who accepted invitations had fallen to 71%, a 10 year low.
The IPPR said health chiefs should have examined the data earlier to find out what was happening.
An independent review set up by ministers will try to establish who was responsible and whether problems should have been flagged up sooner.
All women affected will now be contacted by letter by the end of May and those under 72 will receive an appointment for a catch-up mammogram.
Women aged over 72 can contact a helpline to talk through the pros and cons of having breast screening.
Scans in older women sometimes pick up cancers which do not require treatment.