159 women had missed opportunities to prevent their cancer or have it diagnosed earlier, due to incorrect CervicalCheck test results.
12 of those are deceased, according to a Royal College of Obstetricians and Gynaecologists' review of 1,000 women's slides.
Of those, the British experts say the original test results for 308 women with cervical cancer were wrong.
The report was ordered by the Government in May last year, after a series of scandals affecting CervicalCheck.
Lead Assessor, Professor Henry Kitchener, says despite his report's findings, the screening programme works: