Doctors are hopeful about a new drug to treat skin cancer by causing tumor cells to self-destruct by overloading them with oxygen.

Unlike regular cells, which naturally cannot have their oxidant levels raised beyond a certain threshold, cancer cells cannot balance the amount of free radicals inside them.

With the new drug STA-4783, doctors may be able to overload the cancer cells with oxygen-containing chemicals to the point where the cells cannot cope and simply die off, according to research presented Wednesday at a meeting of the European Cancer Organization in Barcelona.

"We are taking advantage of the Achilles heel of cancer cells," said Dr. Anthony Williams, vice president of clinical research at Synta Pharmaceuticals Corp., based in Lexington, Massachusetts, which paid for the study.

STA-4783, which has no effect on normal cells, is the first of several such drugs planned for study, though no other companies have yet to release results from their research.

It could also be used against other cancers, such as pancreatic or ovarian, as they have been shown to naturally contain higher levels of oxygen. Because cancerous tumor cells already have high oxygen levels, they are easier to overload. Doctors said the study focused on skin cancer, though, as melanoma tumors were particularly deadly.

Williams detailed how the drug doubled the amount of time that advanced melanoma patients survived without their cancer worsening.

The study followed 81 patients with serious skin cancer: 28 received the standard chemotherapy drug paclitaxel and lived an average of 1.8 months, while 53 got paclitaxel plus the new drug and survived an average of 3.7 months.

"This could have a profound effect on patients," said Dr. Alex Eggermont, president-elect of the European Cancer Organization and a surgical oncology professor at Erasmus University in Rotterdam, Netherlands. Eggermont was not linked to the study.

Because STA-4783 targets only cancer cells, Williams said the drug does not come with too many side effects. Less than 5 percent of patients suffered serious side effects, which were similar to those seen in regular chemotherapy treatments, such as a temporary lowering of white blood cells, back pain and fatigue.

Though the study showed patients living longer with the cancer, some doctors said they hoped that, because the drug caused tumor cells to die off, it could potentially be used as a cure.

"Melanoma is so phenomenally complex that we desperately need new drugs to fight it," Eggermont said.

There are very few drugs available for people with advanced skin cancer, which kills 70 percent of patients within one year. Williams said scientific trials offered patients the best hope for living longer.

"There are a few options that relieve the disease, but we have nothing that cures it," said Dr. Jorgan Bergh, a professor of oncology at Sweden's Karolinska Institute.

"This new drug is potentially interesting, but we still need to understand more about how it works and how that may interact with chemotherapy," he said.

Synta Pharmaceuticals will soon start a bigger study with more than 600 patients at 150 cancer centers worldwide.

Other scientists have tried to provoke immune system attacks on skin cancer tumors, but that research is preliminary and scientists have yet to find a permanent way to keep the immune system from attacking healthy cells as well.

"We need to try different, novel approaches to see what might work," Eggermont said, adding that the two methods -- oxygen-overloading and boosting immune defenses -- could even be combined. "If you remove the inhibitions on the immune system and combine that with a drug, then that could open the door to new treatments," he said.

Doctors emphasized that melanoma tumors were different from, and deadlier than, other cancers. For instance, nearly half of all patients with a skin cancer tumor that is 4 millimeters (0.2 inches) thick will die. But for a breast cancer patient with a tumor of the same size, nearly 95 percent of patients will live.

"Patients with advanced melanoma really do not have a lot of options," Williams said. "We only get one chance to save patients' lives, and this may be a good starting point."