Cancer screening services saw almost 150,000 fewer people in the first six months of 2020 compared to last year.
The HSE admits there is a concern cancer diagnoses will be delayed as a result of the backlog in screening.
Cancer screening programmes were stood down during the first wave of COVID-19 earlier this year.
Figures compiled by the Irish Hospital Consultants Association show that as a result just 99,000 people were screened for cancer between January and June, compared to 248,000 in the same period in 2019.
This has caused a backlog in the system, which the HSE admits may result in cancers being diagnosed at a later stage when they're more difficult to treat.
Oncologist Professor John Crown says the problem is worsened by the lack of consultants and capacity in Ireland’s oncology services which is leaving many cancer patients waiting months to see a specialist.
He said: "There's a phrase they used in the civil rights movement that justice delayed is justice denied and I would say the same thing applies in healthcare that treatment delayed is treatment denied."
The HSE says people are not showing up for screening appointments for fear they will contract COVID-19.
Rachel Morrogh, from the Irish Cancer Society, said early detection is key to long-term survival.
She added: "That's why it's so important for people to contact their GP if they notice any potential cancer symptoms."
New figures also show that the number of people waiting for an endoscopy has increased by 56% year on year.
Reporting by Kacey O'Riordan
