The Health Service Executive has said the number of patients being referred to cancer diagnostic services has decreased since the onset of the Covid-19 pandemic.
The National Cancer Control programme said it is concerned that people with symptoms of cancer are delaying seeking medical advice and has encouraged people with symptoms to contact their GP.
The HSE has also encouraged anyone who is worried they might have symptoms of cancer to contact their GP.
In a statement, it said the average number of patients with suspected breast, lung, prostate and skin cancer being referred to hospital clinics is now less than half the number being referred prior to Covid-19 public health measures and it urged people not to delay seeking medical advice.
It said all GP and hospital diagnostic cancer services are continuing to operate, and that precautionary measures are being taken to ensure surgeries and hospitals are safe for patients.
Campaigner Vicky Phelan said the drop in cancer referrals is "very, very worrying" and urged people not to delay in contacting their GP, if they have any symptoms that they are concerned about.
Speaking on RTÉ's News at One, she said that when she first presented to a doctor, she was not experiencing pain but she knew something was not right.
She said: "My worry is that people are going to leave that at the moment and not present because they're worried about going in to see their GP and worrying about getting Covid-19 and maybe thinking that they're worrying over something that may not be there."
Ms Phelan urged people to arrange an appointment with their GP if they have any symptoms, adding "if you know your body, and this is different, you certainly shouldn't be hanging around and waiting."
She said she has been very lucky that she only attends treatment in Dublin every six weeks so she has not had to attend hospital much during this time, but said Covid-19 is a huge worry for people who are undergoing treatment at the moment.
She added that she also knew of checkups that have been cancelled and postponed and that people are "understandably worried".
She said that she has been using cotton masks that her mother made for her and recommended that people make their own or use a snood when in a shop or a crowd.
There have now been a total of 1,375 Covid-19 related deaths in Ireland and 265 new cases of the disease were reported yesterday
Chief Medical Officer Dr Tony Holohan yesterday said that the number of cases coming from the nursing home sector has slowed down.
However, he said, there is still a persistent number of infections in the community, particularly among younger people, a level that is not falling as much as the Department of Health would like.
Around 80% of cases of Covid-19 will be a mild to moderate illness, close to 14% have severe disease and around 6% are critical.
Generally, you need to be 15 minutes or more in the vicinity of an infected person and within 2 metres of them, to be considered at-risk, or a close contact.
Of the 1,375 people who have died due to Covid-19 so far in Ireland, 85.5% of them (1,176 people) had an underlying condition.
So far there have been 376 admissions to intensive care units since the beginning of the pandemic and as of 8pm last night, 82 people are still being treated in ICUs.
An analysis of the first 327 people admitted to ICUs shows that 165 already had chronic heart disease.
76 people (23.2%) had chronic respiratory disease
74 people (22.6%) had diabetes
53 people (16.2%) had a Body Mass Index of more than 40
34 people (10.4%) had asthma requiring medicine
31 people (9.5%) had cancer
20 people (6.1%) had chronic renal disease
Dr Holohan said it was important to point out that there will be overlap between these conditions, where a patient may have more than one.
Earlier this week, he said health authorities are "generally aware of obesity as a significant risk factor, particularly the very obese, in relation to this condition".
The HSE's Chief Clinical Officer also said that as a general principle, severe obesity "plays into immunological status and respiratory reserve".
Dr Colm Henry said there is a "great deal of overlap" between people who have obesity and other chronic conditions, which he said can make someone "more susceptible to the worst effects of the virus".
Additional reporting Laura Hogan