Health officials are concerned that the care of cancer patients will suffer after a charity was dissolved.
Cancer Care Cymru provided specialist nurses at hospitals in south Wales, but the charity said in June that it was folding because of a lack of funds.
The nurses this week worked their final shifts at Velindre Hospital, Cardiff, which provides cancer treatment.
Velindre's director of cancer services, Andrea Hague, said the hospital could not currently afford to replace them.
"They were providing a very valuable service to our patients in the form of support and advice," said Ms Hague.
"We don't have the funds available to take them on so we need to do some work about securing funds for a specialist nurses service.
"In the meantime, we're exploring all options."
Ms Hague said cancer patients would continue to receive "frontline" treatment such as radiotherapy and chemotherapy.
"What will be missing is some of the support and advice that these nurses provided," she said.
"What we're trying to do is see what we can put in place to minimise the impact on patients.
"It's a big blow, we're really disappointed. We see that emotional support as a key part [of the treatment] for patients."
She added: "There are cancer standards that the assembly government sets, one of which is every patient should have access to a specialist nurse."
Keith Hawkins, of Pontypool, Torfaen, said his wife Joy had a brain tumour and had been receiving care from a Cancer Care Cymru nurse at Velindre for nine years.
"She was always there - 24 hours a day if we wanted her. It was always a friendly voice at the end of the phone. You can't bother consultants all the time," he said.
"She used to ring Joy up every month and used to ring me as well because as her carer, I needed help too sometimes.
"Every time you go there [Velindre], she would give you a big hug. All we have there now are nurses that show you to your room before consultancies."
Cancer Care Cymru, which was launched in October 2005, said in June it had been forced to dissolve because the economic downturn had affected fundraising.
The charity provided specialist nurses who worked alongside NHS staff in hospitals such as Velindre, University Hospital of Wales in Cardiff and the Royal Glamorgan Hospital in Rhondda Cynon Taf.
About 10 specialist nurses provided by the charity regularly worked at Velindre.
Ms Hague said charities such as Tenovus and Macmillan Cancer Support also provided cancer services but did not currently provide specialist cancer nurses at Velindre.
The cancer network in south east Wales was due to undertake a review of specialist nurses, she added.
The Welsh Assembly Government said: "The Health Minister, Edwina Hart, asked the chief nursing officer to work with Velindre NHS Trust to ensure patient care is not affected as a result of Cancer Care Cymru being dissolved. Work is ongoing on this matter."