GPs' lack of knowledge about cancer causes side effects of treatment to go undetected, it is claimed.
It is estimated that 500,000 people who have survived cancer develop conditions such as osteoporosis, heart disease and bowel problems.
It is feared GPs fail to pick up on the symptoms of treatment side effects for around half of such patients, Professor Jane Maher, Medical Director of Macmillan Cancer Support, told The Guardian.
Their lack of knowledge coupled with poor communication between hospital specialists and family doctors are to blame for this failing, said Professor Maher.
Research by the government's National Cancer Survivorship Initiative (NCSI) claims up to 25% of people diagnosed with cancer later experience a consequence of their treatment, "which affects their physical or mental health or quality of life."
"GPs and oncologists are failing cancer patients far too often," Professor Maher told The Guardian.
"By not sharing vital information and recording clearly on the patients' medical records they are putting a significant number of cancer patients at risk of having their work, health, relationships and home lives unnecessarily spoiled by long-term side-effects of their treatment.
"GPs need to recognise that people who have had cancer may have health problems related to their treatment, and GPs are the best people to pick these up."
"But that doesn't happen nearly enough at the moment."
Professor Maher also criticised the record keeping of some general practices.
She claims GPs are not updating a cancer patient's medical records with their treatment details as they "don't realise why it's important".
She said GPs "need to do much more" to ensure records are up-to-date.
Dr Clare Gerada, Chair of the RCGP, said GPs need help to more quickly diagnose the side effects of cancer treatment.
"If Professor Maher and the NHS tell us exactly what cancer someone has had, and what treatment, and what the possible risks are of that, and in a way that's easy to understand, we will do things better," she said.