Hundreds of cancers are not discovered until they have progressed to the most deadly stage of illness in Bucks, new figures show.
A "cancer catastrophe" could be on the cards if more is not done to reduce the number of people receiving late diagnoses, according to charity Cancer Research UK.
At least 511 cases diagnosed by medics in the NHS Buckinghamshire CCG area had reached an advanced stage at the point of diagnosis that year.
Cancer Research UK said there are concerns that survival rates could "go backwards" as a result of the coronavirus pandemic's impact upon the NHS.
Before cancer patients embark upon treatment, doctors commonly use staging techniques to establish how severe the disease is and how far it has spread.
The stages, which range in severity from zero to four, are used to describe the size of tumours and to determine how far the cancer has spread from where it originated.
There were 2,976 cancers diagnosed in Buckinghamshire in 2019 and stage four diagnoses, which carry the greatest mortality risk, represented 25% of those with a valid stage identified.
That was around the same as recorded the year before.
Figures for CCGs across England show some cancers are far more likely to be diagnosed late than others, with those affecting the pancreas, lungs and oesophagus among those the most likely to be detected at an advanced stage – often because they do not cause symptoms until a later stage.
They are among those represented by the Less Survivable Cancers Taskforce, which launched in 2017.
The taskforce, made up of six different charities, is launching its first awareness day on January 11 to highlight the importance of early diagnosis in improving survival rates.
In the area covered by the NHS Buckinghamshire CCG, 43% of the 284 lung cancers detected in 2019 were at stage four when found, as were 42 of 99 pancreatic cancers and 25 of 69 oesophageal cases.
Patients diagnosed at the earliest stage are between five and 10 times more likely to survive at least five years compared to those diagnosed at stage four.
Dr Jodie Moffat, head of early diagnosis at Cancer Research UK, said reducing the number of people diagnosed with advanced disease was crucial to saving lives and swift action was needed from the Government and NHS.
Dr Moffatt added: “Many factors can impact late diagnoses, and Covid has affected many of these, such as how readily people come forward with symptoms, or how long people need to wait for tests.
"Worryingly, waits for a cancer diagnosis and treatment were struggling well before the pandemic hit.
"Chronic shortages in staff and equipment mean cancer waiting times have been missed for years."
An NHS spokeswoman said the health service was committed to ensuring that 75% of cancers are detected at stage one by 2028, adding that 95% of those diagnosed since March 2020 began treatment within a month.
A Department of Health and Social Care spokesman said cancer diagnosis and treatment is a priority for the Government, adding that £10 billion was being invested in cutting waiting times.