Up to 270 women in England may have died because they did not receive invitations to a final routine breast cancer screening the Health Secretary Jeremy Hunt says.
Speaking in the Commons he said 450,000 women aged 68-71 had failed to get invitations since 2009.
Mr Hunt has announced an independent review and apologised wholeheartedly to the women and their families.
He said oversight of the NHS screening programme had not been good enough.
GPs leaders said they were shocked to learn of the error and said the implications for GPs would potentially be significant.