Before March 2020, there were about one million women eligible for NHS screening who were not being checked for signs of the disease, Breast Cancer Now said.
Between then and May this year, when the government started to lift Covid restrictions, there had been about 1.5 million women who had not been screened, the charity said.
As a result, by the end of May, as many as 12,000 people could have been living with undiagnosed breast cancer, Breast Cancer Now estimated.
The charity is using Breast Cancer Awareness month to call on Westminster to urgently set out how £50m of additional funds will be used to ensure all women living with undiagnosed breast cancer are identified and treated without more delay.
An additional 10,000 people would need to start treatment over the coming months until spring 2022 for NHS England to meet its 22 March target of tackling the shortfall in people starting cancer treatment.
In Wales and Northern Ireland, it will take three to four years for screening services to tackle the backlogs, Breast Cancer Now said, citing recent data.
The charity is calling on ministers across the UK to invest funds long-term into the cancer screening workforce to ensure “prompt breast cancer diagnosis and treatment is guaranteed both now and in the future”.
NHS staff – who the charity said were “already under-resourced and over-stretched prior to the pandemic” – are at risk of being overwhelmed by demand for screening services now that domestic Covid restrictions have been lifted for several months.
Baroness Delyth Morgan, chief executive of the charity, said that the increase in the number of women potentially missing breast cancer screening services was “staggering”.
She added: “Women with breast cancer are continuing to pay the price due to the impact of the pandemic, and in the worst cases delayed diagnoses could mean that some women die of this devastating disease.
“Quickly finding and treating those with undiagnosed breast cancer must be a priority.
“Governments across the UK must urgently ensure there is sufficient investment to do this – these women do not have time to wait.”
Dr Jeanette Dickson, president of the Royal College of Radiologists, said: “Breast services, including screening, are working flat-out to make sure patients are seen as quickly as possible, and we cannot urge people enough – if you have any worrying symptoms, please seek help from your GP. If you are given a screening appointment, please take it.
“But breast imaging and treatment services were massively under-resourced even before the pandemic hit.
“Now, screening teams are trying to fit two years’ worth of appointments into one to catch up with a backlog of millions, while struggling with long-standing staff shortages and woefully substandard facilities, as well as slower working due to covid restrictions.
“If the government is serious about improving breast cancer outcomes and tackling the backlog then in the short-term it has to continue investing in scanners and IT connectivity, as well as push through stalled service improvements.
“But ultimately, we cannot get away from the need to invest in people. The NHS needs more imaging and oncology staff to ensure future breast cancer patients get the care they deserve.”
Breast cancer is the most common cancer in women in the UK. Women registered with a GP are invited for a mammogram between the ages of 50 and 53 every three years until their 71st birthday.
The NHS Breast Screening Programme helps detect breast cancer at the earliest possible stage, preventing around 1,300 women dying from the disease each year across the UK.
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