Chronic myeloid leukaemia (CML) patients are often required to take tyrosine kinase inhibitors (TKIs) indefinitely.
But 93% of those in a new study stayed cancer-free after stopping or reducing treatment.
Cancer Research UK said the results were "promising" but dosages should not be changed without a doctor's advice.
In 2000, trials of TKIs proved successful in controlling the rare disease, but also had side-effects,  including an increased risk of infection, skin rashes, nausea, hair loss and in some cases hormone disorder and a build of fluid around the heart.
The follow-up study, led by the University of Liverpool and involving consultants from Newcastle's Freeman Hospital, saw patients being given half the standard dose for the first 12 months. If leukaemia levels remained low, the drug was then stopped completely.
So far, out of 174 patients tested, 93% have shown no evidence of their leukaemia relapsing one year after reducing their dosage and many reported a significant decrease in side-effects within the first three months.
Source: CML Support
Dr Wendy Osborne, who is leading the Destiny study in Newcastle, said: 'We've gone from having patients with a potentially incurable disease and requiring toxic chemotherapy and transplantation, to now selecting some patients, again in a clinical trial setting, to stop the drug completely to remove any side-effects they have.
"This in itself is moving towards saying we've cured some patients and this is all because of research."
Dr Ã

It could lead to new ways of diagnosing the condition and of testing the effectiveness of new drugs.
The technology, reported in the journal Neuron, can identify inside a living brain clumps of a protein called tau that is closely linked to the disease.
Alzheimer's Research UK said it was promising work.
Alzheimer's disease is a problem for researchers trying to come up with a cure. The brain starts to die years before any symptoms are detected, which means drugs are probably given too late.
A diagnosis of Alzheimer's cannot be made with absolute certainty until a patient has died and their brain is examined. It is also not 100% clear what is the cause of the dementia and what are just symptoms.
One protein, called tau, is very closely linked to the disease, with tangles of tau thought to be one way in which brain cells are killed.
The team, lead by the National Institute of Radiological Sciences in Chiba, used positron emission tomography to build a 3D picture of tau in the brain.
They developed a chemical that could bind to tau and then be detected during a brain scan.
Tests on mice and people with suspected Alzheimer's showed the technology could detect tau.
Dr Makoto Higuchi, from the National Institute of Radiological Sciences in Japan, said: "Positron emission tomography images of tau accumulation... provide robust information on brain regions developing or at risk for tau-induced neuronal death."
The research is at an early stage, but it could eventually lead to an actual test for Alzheimer's disease.
It might also allow researchers to closely follow the impact drugs that affect tau have on the brain.
Another protein - beta amyloid - is also linked to Alzheimer's and can be detected in similar tests.
Dr Eric Karran, director of research at Alzheimer's Research UK, said: "This promising early study highlights a potential new method for detecting tau - a key player in both Alzheimer's and frontotemporal dementia - in the living brain.
"With new drugs in development designed to target tau, scans capable of visualising the protein inside the brain could be important for assessing whether treatments in clinical trials are hitting their target.
"If this method is shown to be effective, such a scan could also be a useful aid for providing people with an accurate diagnosis, as well as for monitoring disease progression."

The Anthony's chain of food outlets included restaurants in the city's Corn Exchange building and a patisserie in the Victoria Quarter.
The firm was founded in 2004 by chef Anthony Flinn and his father, also called Anthony Flinn.
Lines Henry Ltd have been appointed as administrators and said there was not enough money for the firm to continue trading.
Michael Simister, of Lines Henry, said: "It is sad when such a well-known business runs into difficulties.
"Unfortunately, the business has had to close, with the loss of 70 jobs, because there is not enough money available to continue trading."
He added despite good reviews the business had struggled with increased competition and difficult economic conditions.
New research could see patients with a rare blood cancer live longer without the side-effects of drugs, doctors say.
[NEXT_CONCEPT]
Pioneering brain imaging that can detect the build-up of destructive proteins linked to Alzheimer's has been developed by Japanese scientists.
[NEXT_CONCEPT]
The failure of a restaurant business in Leeds has led to the loss of 70 jobs.