GP leaders said the decision to put individual practices' performance data on cancer into the public domain may force GPs to lower their thresholds for investigation for fear of appearing to miss a diagnosis.
Heightened scrutiny from commissioners, patients and the media raises the risk of unnecessary testing and treatment, all at an increased cost to the NHS, the GPC said.
The RCGP said GPs referred over 70% of patients with suspected cancer within one or two consultations, and called for improved access to cancer tests.
From Tuesday, patients in England can view their practice's 'cancer profile', which includes the number of cancers diagnosed, the number of people who have screening and the numbers sent through the two-week wait referral pathway. Commissioners can use the data to benchmark performance.
The data, published by the National Cancer Intelligence Network (NCIN), show a three-fold variation in GP urgent referral for cancer.
Practices in England referrred an average of 1,812 patients per 100,000 of the population under the two-week wait pathway in 2010/11, but this varied from 830 to over 2,550 between practices.
But the figures are only adjusted for age and not for deprivation, cancer prevalence or other factors. Practices with fewer than 1,000 patients were left out.
GPC deputy chairman Dr Richard Vautrey said: 'While it is important that practices have access to good quality information about their clinical practice, the risk of publishing data like this is that it will be used by PCTs and clinical commissioning groups (CCGs) to reduce referrals while at the same time by the media to increase referrals.
'In a society that cannot cope with risk, the result could be that GPs will feel pressured to reduce the threshold at which they make a referral for fear of being seen to miss any diagnosis. This will place patients at risk of unnecessary investigations or treatment and put further financial pressure on the NHS.'
Variation 'very worrying'
The publication is part of the government's drive to release more NHS data.
The cancer profiles show how many patients were urgently referred for suspected cancers such as breast, lower GI and skin cancer. It also includes how many died of the disease and screening uptake, among other data.
Dr Mick Peake, clinical lead for the NCIN, said: 'The data are not easy to interpret since we do not know what the "optimum" level is for these measures and although the data are adjusted for age, there may be other differences in the characteristics of the patients of a particular GP practice that impact on local referral rates.
'However the range of the variation is so wide that, at the extremes, it probably reflects differing standards of care.'
The organisation said the data have already 'proved valuable' to practices to benchmark their performance.
Sarah Woolnough, executive director of policy and information at Cancer Research UK, said: 'It’s very worrying to see a more than three-fold variation in the rate of urgent cancer referrals among GPs. And although the number of people GPs suspect have cancer and send for further tests will naturally vary depending on the age and demographic of their patients this level of variation suggests differing approaches by some GPs.'
She added: 'We urgently need to learn more about what’s behind these differences and tackle poor practice.'
An RCGP spokeswoman said: ‘These practice profiles contain a wealth of information about the important contribution that GPs make to saving lives from cancer, including how well they do in screening for cancer, investigating patients and referring promptly those who need specialist assessment.
'There are some patients where we do, for various reasons, have difficulty in making a rapid diagnosis and we must always be looking at how we can do better and do more. There is no doubt that giving GPs greater and improved access to cancer tests would be a major step forward.'