The Government is "losing control of cancer care", with waiting times for treatment soaring over the past eight years, Labour has said.
Research carried out by the party found that one patient waited 541 days for treatment following a GP referral in 2017 - against a target of 62 days.
Another was forced to endure a wait of 254 days for treatment following a decision to treat, against a target of 31 days.
The figures, which follow Freedom of Information (FOI) requests to acute and community health trusts in England, show the "average longest" wait reported by each trust rose to 213 days - 16 days higher than in 2010.
Labour found that 66% of trusts who replied (58 out of 88) had at least one patient waiting longer than six months and 69% (60 of 88) had a worse longest wait than in 2010.
Every trust which replied apart from two said that at least one patient had waited more than 62 days for treatment.
One patient waited 377 days for a consultant appointment following a GP referral, against a target of 14 days.
The longest waiting time of 541 days for treatment following a urgent referral was endured by a patient at Royal Devon and Exeter NHS Foundation Trust, while a patient at Hull and East Yorkshire Hospitals NHS Trust also had to put up with a wait of 446 days.
Shadow health secretary Jonathan Ashworth said: "The number of people needing cancer treatment has risen sharply in the past 10 years and the Government has simply failed to increase availability of services at the rate required.
"The truth is that the brilliant efforts of NHS staff around the country to deliver the best for their patients are being hampered by tight NHS budgets.
"Years of under-funding and abject failure to invest in the frontline doctors and nurses we need means Theresa May is letting down cancer patients.
"Now we know the astonishing truth that some patients are waiting a year or more just to get treatment. It's simply not good enough.
"With cancer targets repeatedly missed and with the ongoing scandal in breast screening, it adds to the sense that the Government is losing control of cancer care in this country.
"For Labour it will be a priority to make sure cancer services are properly resourced and properly staffed to provide the best possible care to all cancer patients, no matter what part of the country they live in."
Andrew Kaye, head of policy at Macmillan Cancer Support, said: "These findings show that despite the tireless work of doctors and nurses, it appears that some cancer patients are still enduring shockingly long waits to start treatment.
"Long delays can put people under incredible stress at an already difficult time and could also mean that someone's health could take a turn for the worse.
"Such figures underline how vital it is that the Government supports the NHS to improve waiting times this year."
A Department of Health and Social Care spokesman said: "Cancer care has improved significantly in recent years, with around 7,000 people alive today who would not have been if mortality rates stayed the same as in 2010.
"Nobody should wait longer than necessary for treatment and, despite a 115% increase in referrals since 2010, the vast majority of people start treatment within 62 days - backed by our £600 million investment to improve cancer services."
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