- Video Report by Social Affairs Editor Penny Marshall
The Health Secretary estimates that between 135 and 270 women have "had their lives shortened as a result."
The "computer algorithm failure" that occurred in 2009 and ran through to 2018 meant that many women who were aged between 68 and 71 during that period were not sent their final breast screening invitation.
- How do I know if I'm affected?
Public Health England fixed the problem in April and no women will be affected going forward.
An effort has been launched to contact all the women who missed invitations before the end of May. This week the first 65,000 letters will be sent out.
- What happens if I am affected?
All women under 72 who are affected will receive an appointment letter informing them of their time and date.
Women aged 72 and older will be able to contact a dedicated helpline to discuss whether a screen could benefit them.
Women can seek advice by calling the helpline on 0800 169 2692.
- Who is eligible for a breast screening?
Any woman concerned that they might have breast cancer can see their GP and be referred for a screening.
As the likelihood of breast cancer increases with age, all women aged between 50 and 70 years old who are registered with a GP should automatically be invited for screening every three years.
- How effective is the screening?
Screening allows breast cancer to be diagnosed in its infancy, making it easier to treat. It involves a mammogram to check for signs which are too small to see or feel.
It is the most effective procedure at diagnosing breast cancer at an early stage.
- What are the signs of breast cancer?
The first symptom most often noticed by women is a lump or thickened tissue in their breast. Most lumps are not cancerous but it is best to have them checked by a GP.
Other symptoms included a change of size in breasts, bloodstained discharge from nipples, a change in the appearance of your nipple, a lump or swelling of your armpit and a rash on or around your nipple.
- What is the survival rate of breast cancer?
Breast cancer is the most common cancer in the UK, with around 150 diagnoses every day - accounting for 15% of all new cancer cases.
But, survival is improving and has doubled in the last 40 years in the UK.
Around two-thirds (65%) of women diagnosed with breast cancer in England and Wales survive their disease for twenty years or more.