(June 25) -- An experimental pill seems to be an effective treatment for cancerous tumors that don't respond to standard treatment. Researchers said that the drug olaparib helped two-thirds of patients with inherited types of cancers, including breast, ovarian and prostate cancer, according to a report from WebMD.

The drug was used in a small study on patients with mutations in the BRCA1 gene, which raises a woman's risk of breast and ovarian cancer, and the BRCA2 gene, which boosts a person's risk of prostate cancer. In more than half of the cases in which patients took olaparib, cancerous tumors shrank or stopped growing, a British researcher said.

Olaparib is one of a group of drugs called PARP inhibitors that keep unstable cancer cells from growing. The drugs "will very likely change the way we treat patients" with inherited forms of cancer, doctor Daniel Silver told WebMD. Silver, who was not involved in the olaparib study, works at the Dana-Farber Cancer Institute in Boston.

Robert Bazell, the chief science correspondent for NBC News, hailed the research as "the most exciting development in cancer research in a decade or more."

In a commentary posted on msbnc.com, Bazell said the drugs could save thousands of lives and fundamentally change treatments for several forms of cancer.

"Of course, as with any good science, it is not just that one report that generates such excitement," Bazell wrote. "The new research builds on many years of solid basic science and on other clinical trials that are either completed or in progress, which appear to show similarly dramatic reduction of certain breast, ovarian and prostate cancers."

Bazell pointed out that some of the patients in the study avoided side effects like nausea and hair loss that result from other cancer treatments.

His piece provides concise background information on how PARP inhibitors work against inherited types of cancer.

The research was published Wednesday in the New England Journal of Medicine.