Just over one in five urgent breast cancer referrals made in June in the Northern Trust were seen within the recommended two-week target.
That's according to Ulster Unionist MLA Roy Beggs, who claimed it's the third month in a row that the target was widely breached.
Northern Ireland's six healthcare trusts aim to have 100% of urgent breast cancer referrals seen within 14 days.
Mr Beggs condemned what he described as a crisis in breast cancer services in the Trust.
"It is well known that early diagnosis and treatment saves lives and for many cancer patients and their families, time is unfortunately a luxury that very few can afford. Cancer is a particularly cruel and unpredictable disease so there should be no opportunity for or tolerance of delays," he said.
A spokesperson for the Northern Trust said they could not validate that Mr Beggs' waiting time figures for June were accurate.
In June, Cancer Research UK described cancer waiting times in Northern Ireland as "unacceptable" after it was revealed 200 people were not seen by a breast cancer specialist within the Department of Health's 14-day target.
“I have long been concerned about the delivery of breast cancer services in the Northern Trust," said Mr Beggs.
He said it's the second time he has drawn attention to targets being missed when it comes to breast cancer referrals.
"When I revealed last year that those delays had become so serious, the Northern Trust tried to allay concerns by saying that they were taking immediate action to secure additional in-house breast assessment clinics in Antrim as well as in a neighbouring Trust," he said.
"What makes this most recent deterioration even more serious is that the Northern Trust has again already requested urgent support from other Trusts, but this time they are unable to provide assistance as they too are experiencing their own capacity issues," he said.
In a statement, the Northern Trust said the stark reality is that they have insufficient resource to meet current demand in the Northern Trust area and that demand is growing, as is the case elsewhere.
"The Department of Health’s consultation document on breast assessment stresses that there is strong clinical consensus in support of the view that the current regional service provision is no longer sustainable.
"As a result, services are fragile with factors such as staff sickness, staff departures and even staff leave posing significant problems. As a result, we see longer waiting times which is just not acceptable, particularly for red-flag patients," said a spokesperson.
Roy Beggs, the Ulster Unionist Party's health spokesperson, said: "I have been informed that the Northern Health Trust had budgeted for 2,880 red flag breast cancer patients in 2019/20 - 240 a month. Whilst it may sound significant, the reality is that there were 465 red flag referrals received in the month of May 2019 alone - almost double the service’s core capacity for the month."
"I believe a fourth weekly breast clinic will commence in September 2019, but even this will still not be enough to fully meet current demand.
He said the system of having five Trusts in Northern Ireland managing separate services is failing patients - and that with no local Health Minister or Executive, he has serious concerns about how the situation has developed.
“We urgently need someone - either a local Health Minister or a Direct Rule Minister - who is empowered to drive much-needed improvements in our local health service."