Singer Linda Nolan and presenter Bill Turnbull are among the celebrities with cancer who are urging the public not to put off seeking important checks.
Concerns have been raised that people have delayed coming forward because of the coronavirus pandemic.
The number of people getting cancer checks in June dropped sharply compared with the previous year.
Linda and Anne Nolan recently announced they had been diagnosed with cancer within days of each other.
Linda, 61, said the public should feel “absolutely safe in the hands of the NHS” and praised its “heroic work”.
Turnbull said cancer “unfortunately did not disappear” during the coronavirus outbreak, and urged people not to delay getting checked if they had concerns.
The pair are taking part in a new campaign. Around 141,600 people were referred for cancer checks in June, compared with almost 200,000 during the same month last year.
Nearly half of the public have said they had concerns about seeking help amid the pandemic. One in 10 said they would not contact their GP even if they had a lump or a new mole.
Linda Nolan has been having treatment for liver cancer, while Anne, 69, has stage three breast cancer.
Linda said she had received “exceptional” care and praised the NHS for working “to continue to deliver the vital care we all need, even as they deal with the ongoing pandemic”.
She added: “It’s so important people get checked out when they need to. Cancer doesn’t wait, and timing is everything. It might be the very thing that makes all the difference.”
When former BBC Breakfast host Turnbull revealed his diagnosis in 2018, it led to a 36% jump in people being referred for prostate cancer.
He said: “Cancer is a cruel disease and unfortunately it did not disappear during the coronavirus outbreak.
“We know that it’s all too easy to put something like this off, but please do contact the NHS if you have any signs of cancer.”
Professor Peter Johnson, NHS clinical director for cancer, said waiting to get help could have serious health consequences.
He said: “We cannot let Covid become a reason for people not to get checked for cancer – NHS staff up and down the country have worked very hard to make sure that tests and treatment can go ahead quickly and safely.
“Cancers are detected earlier and lives are saved if more people are referred for checks, so our message to you is to come forward – it could save your life.”