"They've utterly changed my life," said Cowley, 70. She credits the treatments with enabling her to live long enough to welcome six grandchildren into the world.
Unlike most terminally ill cancer patients, Cowley had the chance to try untested drugs. With the opening of a government-run network of experimental cancer clinics across the country this month, British doctors are now hoping to offer millions of other dying cancer patients the same chance.
The network builds on an existing set of cancer research centers first established in 2002 to bring laboratory advances quickly to patients. Each center will receive 2 million pounds (about $4 million) from the Department of Health and Cancer Research United Kingdom to develop new treatments.
Under the government-supported trials, Cowley has tried at least four experimental medicines for free. Her doctors aren't sure which ones have had the most impact but say her situation is stable.
In the United States, cancer patients can also sign up for experimental treatment, but there is no official national effort to help patients enroll. Most trials are run in academic centers while 80 percent of cancer patients are treated in community hospitals. The American Cancer Society offers a matching service to line up suitable experimental trials for cancer patients, but success rates vary.
There is also a government-run Web site that attempts to provide trial listings for all diseases, but companies often don't post experimental trials for proprietary reasons and to avoid being inundated with volunteers. According to a 2005 report, 20 percent of cancer patients in the U.S. are eligible to participate in drug studies, but only about 3 percent enroll.
In Britain, there are now 19 centers across the country where terminally ill patients can apply to try untested drugs, if they have exhausted all other treatment options. While there are clinics in France, the Netherlands and Italy that offer cancer patients experimental treatments, no other European country has a similar national network.
It is usually rare for patients with late-stage cancer to have opportunities to try experimental drugs, and experts estimate that only hundreds in Britain currently have access. But with more centers now open, officials hope that thousands will soon benefit.
The government initiative also aims to speed up the drug testing process. Some experts estimate there are up to 500 potential new drugs in the pipeline, many of which are stuck in the research phase as scientists recruit human volunteers.
Getting new cancer drugs usually takes a decade, from the time they are developed in the laboratory to the time they are licensed for patient use. "We want to cut that timeline in half," said Dr. John Gribben, professor of experimental cancer medicines at the St. Bartholomew's and London hospital, home of one of the clinics.
The experimental clinics will run early trials, using drugs that have never been tried in humans before. The drugs have been tested in laboratories and in animals, but scientists and doctors will have to monitor patients closely to see if the drugs really work inside humans and to watch for dangerous side effects.
"We will take regular samples from patients to quickly assess whether or not the drugs are doing what we want them to do," Gribben said.
One of the biggest challenges is guessing what the appropriate dose might be. "The only way to know the right dose, to work out how toxic a drug is and if it's hitting a target, is for someone to try it," said Dr. Karol Sikora, a cancer expert at Imperial College School of Medicine at Hammersmith Hospital, London. "The risk is usually small, but there's always some risk involved."
Doctors usually start with a very low dose and gradually increase it until the drug is working or patients can't tolerate it. But things can still go wrong.
In 2006, six previously healthy volunteers developed convulsions, suffered organ failure and lapsed into comas hours after being injected with a new drug intended to treat leukemia and auto-immune diseases at Northwick Park Hospital in London. One man has since been diagnosed with cancer.
Critics have said that expanding drug tests for terminal cancer patients preys on the desperation of dying people.
But some ethicists say that as long as patients are told about the potential side effects, the process is fair.
"How can you lower the bar too much for people who are going to die anyway and for whom this is a last hope?" said John Harris, a professor of bioethics at the University of Manchester. "We're offering them a chance when they have nothing to lose."
Still, it is a very slim chance. Early trials are only designed to test if drugs are safe, not whether or not they actually work.
"There's only a five percent chance that patients will get any benefit," said Dr. Franco Cavalli, a cancer expert with the European Cancer Organization.
In Britain, several agencies monitor the safety of experimental cancer tests, including the Medicines and Healthcare products Regulatory Agency and the European Medicines Agency.
In the United States, all study designs must be approved by the Food and Drug Administration before the trials can start. To safeguard patients' safety, the medical center conducting the trial must also have the consent of an independent group of experts. The Office of Human Research Protections, a government agency, also works to protect people involved in federally-funded research.
For patients like Cowley, for whom standard cancer treatments have failed, experimental drugs are her only option. She estimates she has tried four different new drugs, some of which have progressed into further testing.
"It never occurs to me that I'm a guinea pig," Cowley said. "I know the doctors need to test the drugs to find out if they work or not, but for me, I just want to carry on living."