Charities including Macmillan and Cancer Research UK say the system is struggling to cope with increasing demand.
The most recent set of figures, published by the Department of Health at Stormont, show that for the month of September just 48.2% of patients had started treatment within 62 days of an urgent referral for suspected cancer by a GP.
In September 2018 the figure was 62.1% and the year before it was 62.4%. In September 2016, the figure was slightly higher again at 63.2%.
The figure of 48.2% is the lowest ever recorded since the Department of Health first started recording the cancer waiting time statistics.
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The target is to ensure 95% of patients begin treatment within 62 days.
Heather Monteverde, head of Macmillan Services for Northern Ireland, said the figures show many people are “continuing to face anxious delays to get a cancer diagnosis and start treatment”.
She added: “Consistently missed targets for cancer waiting times are once again indicative of a system struggling to cope with increasing demand, despite the efforts of healthcare professionals within all of our trusts who continue to work tirelessly to support patients.
“Without an NI Assembly, people living with cancer in Northern Ireland are being disadvantaged.
“We need our decision-makers in place urgently to progress transformation of the healthcare system and to ensure that the cancer strategy under way is properly costed and urgently implemented; to prioritise investment so that our health service can retain, develop and employ enough health care professionals with the right skill mix; and to ensure that as demand increases, people living with cancer receive quality, person-centred care.”
Margaret Carr, speaking on behalf of Cancer Research UK, said: “Despite the best efforts of staff, this report tells us that some people in Northern Ireland are waiting too long for cancer treatment.
“For many, this is an anxious time. This is concerning, especially as demand on cancer services is rising.
“To help our trusts cope and ensure patients are diagnosed quickly and at an earlier stage, a long-term workforce plan is urgently needed. This needs to address staff shortages now and in the future.”
UUP MLA Roy Beggs said the figures show the need for the government in London to step in while the political deadlock continues in Belfast.
“Cancer is a cruel disease that often thrives during periods of delays in diagnosis and treatment,” Mr Beggs said.
“It is a total disgrace that the ongoing impasse at Stormont is getting in the way of resolving the pressures. If there is no deal by Monday the Westminster government must step in and immediately take back responsibility for health matters. Only then could there be a chance of better outcomes for local patients.”