The insurance industry unfairly penalises people with cancer, charity Cancerbackup has claimed.
Travel insurance is being denied to many, according to Cancerbackup
It has said people are being turned down for travel insurance, or being charged much higher premiums - even when they are free of the disease.
A Cancerbackup survey showed that nearly 90% of those affected by cancer found it hard to get travel insurance.
Insurers say cancer is not singled out. Pre-existing conditions are treated the same, industry figures say.
The charity's research suggests that former sufferers are faced with "blanket bans on cancer" by companies.
The survey showed that sales staff were insensitive and 70% of people found the experience of trying to obtain travel insurance distressing.
And, in a "mystery shopper" exercise, Cancerbackup also found that most companies do not provide cover for cancer because individual situations are not taken into account, so people are automatically classed as high risk.
Researchers found that only 1.6% of people surveyed said they had made a cancer-related claim on travel insurance in the past and the majority of people - 70% - were told they were fit to travel by their doctors.
It also emerged that people are being quoted unaffordable premiums that run into thousands of pounds.
And more than one in 10 of those surveyed were forced to cancel their trip, while one in 20 travelled with no insurance.
Such a move would leave them at risk of not being covered for any form of emergency.
Joanne Rule, Cancerbackup's chief executive, said: "Travelling without cover for cancer can be a huge personal risk."
She went on: "We know anecdotally that if you need to claim for any illness at all, there is a presumption by insurance companies that is it related to your cancer, and you will need to prove that it is not. Ms Rule urged the insurance industry to "act now" and "start listening to people with a history of cancer."
She added that travel insurance companies could "open themselves up to a huge growing market of potential customers" if they were to take people's individual circumstances into account when assessing risk.
Ayesha Owusu-Barnaby, of the charity Macmillan Cancer Support, said the findings were not surprising.
"Cancer patients tell us there are huge inconsistencies in how they are treated when applying for insurance; they are either refused point blank or can only secure insurance with much higher premiums.
"This problem is only set to get worse as there are now more than one million people in the UK who have had a cancer diagnosis. The insurance industry needs to recognise that not all cancers are the same and treat people accordingly."
A spokesperson for the Association of British Insurers said: "This report underlines the importance and value of shopping around, either independently or through a broker, in order to get the best and most appropriate insurance policy.
"Specialist cover is available in the market, and as long as people are fit to travel, even if they have a terminal illness, they will be able to get travel insurance."