'Beyond belief that breast screening failure lasted for nearly a decade'It is believed around 300,000 women who were impacted by this failure are still alive and in their 70s.
What is breast cancer screening?
Screening is a procedure which allows doctors to catch breast cancer while it is still in its infancy and therefore easier to treat.
It involves an X-ray test - known as a mammogram - to check for signs of cancer which are too small to see or feel.
Any woman concerned that they might have breast cancer can see their GP and be referred for a screening.
But in recognition that the risk of getting breast cancer increases with age, all women aged between 50 and 70 who are registered with a GP should automatically be invited for screening every three years.
How are they invited?
The screening process is overseen by Public Health England, which uses an IT system to send out invitations.
What exactly has gone wrong in this process?
The Health Secretary said there was a "failure" stretching back to 2009 with a computer algorithm used to send invitations.
An upgrade to the invitation IT system provided improved data to local services which led to the problem being identified. Issues included the method by which age parameters are programmed into it, Mr Hunt said.
This meant that between 2009 and the start of 2018, an estimated 450,000 women aged between 68 and 71 were not invited to their final breast cancer screening.
Of that figure, around 309,000 women are still alive.
The Yorkshire Post says: Another day, another crisis, as breast screening scandal revealedCould anyone have died due to this error?
At this stage the best estimate available indicates there may have been between 135 and 270 women who "had their lives shortened as a result", Mr Hunt said.
Why has this happened?
An independent review has been set up to establish exactly why the problem happened in the first place and why it was not noticed for so long.
How do I know if I'm affected?
Public Health England fixed the problem by April and no women will be affected going forward, according to Mr Hunt.
Efforts will now be made to contact all the women who missed invitations before the end of May. This week the first 65,000 letters will be sent out.
"We hope to reassure anyone who does not receive a letter this month that they are not likely to be affected," the Health Secretary said.
What happens if I am affected?
The letter should explain the next steps to be taken, advising all those under the age of 75 that they will "automatically be sent an invitation to a catch-up screening", Mr Hunt said.
Those aged 72 and over will be given access to a helpline offering clinical advice about whether or not a screen is appropriate.
Work is being done with devolved administrations in other parts of the UK to offer support to women who might have moved to the area from England.
Emma Greenwood, Cancer Research UK's director of policy and public affairs, said: "If you suspect you have been directly affected by this or if you are over 50 and haven't had a mammogram in the last three years and would like one, the NHS Choices website provides further information and the option to contact your local unit to book an appointment."