Almost two-thirds of cancer patients do not fully understand what their diagnosis means, research suggests.
Jargon can be confusing for many
Only half of those surveyed knew that when their doctor said "the tumour is progressing", it was not good news.
Experts say the study, based on more than 200 responses, shows many patients are lost in a "maze of information".
The research was carried by the charity Cancer BACUP, campaigning group Ask About Medicines, and the Association of British Pharmaceutical Industries.
It also found that almost one in three cancer patients feel that those who are better informed get better care.
Yet nearly four out of 10 did not feel they knew what questions to ask about their treatment options - and only half felt encouraged to ask questions at all.
The findings are to be presented to the Department of Health by Ian Gibson, chair of the All Party Parliamentary Group on Cancer.
Campaigners are calling for health professionals to develop ways to provide patients with easy-to-understand information, and to encourage them to ask questions.
Joanne Rule, chief executive of CancerBACUP, said: "Information is set to replace money as the health currency of the future which suggests a whole new debate about equality between the well informed and those who are left in the dark.
"Cancer patients today are faced with increased treatment options, including innovative medicines.
"But if they lack information, they are unable to be as involved as they should be in all aspects of their care."
Joanne Shaw, director of Ask About Medicines, said: "It's vital that people with cancer are encouraged and empowered to ask questions, as patients who have a better knowledge of their condition are better equipped to manage their symptoms as well as being more positive."
Kate Tillett, of the ABPI, said the study proved there was no substitute for a good open relationship between cancer patients and healthcare professionals.
"We hope it will serve as a call to action to healthcare professionals to develop information prescriptions for their patients and encourage them to ask questions about their treatment."
National Cancer Director Professor Mike Richards accepted that good information and face-to-face communication were essential to the delivery of high quality care.
He said: "We know that the provision of information to cancer patients has improved over the past five years.
"This is almost certainly due to the establishment of specialist cancer teams and the vital contribution of clinical nurse specialists.
"However, the report highlights the gaps remaining in the provision of information to cancer patients.
"That is why the Department of Health is working closely with cancer charities to improve services."