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Join Date: Feb 2008
Location: South East Wisconsin
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(PARP inhibitors) Experimental cancer drugs cut tumors off from repair tools
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By Liz Szabo, USA TODAY
Margo Adler-Libstag isn't cancer-free.
But the Vermont mother of two says an experimental drug is keeping her rare form of ovarian cancer in check, leaving her feeling fairly well most of the time.
"You always want cancer out of your body," says Adler-Libstag, 51, whose cancer has spread throughout her abdomen. "But people live with chronic disease. I could live with a little bit of cancer, as long as it's stable and I have a good quality of life."
FORUM: Living with Cancer
Adler-Libstag says the 16 pills she takes each day as part of a clinical trial fight cancer in a new way — by robbing her tumors of the tools they use to repair themselves.
FIND MORE STORIES IN: Georgetown University | American Society of Clinical Oncology
Researchers this weekend will discuss the results of several studies of these new drugs, called PARP inhibitors. Although the drugs haven't yet been studied in the kind of large, rigorous studies required for Food and Drug Administration approval, early studies appear promising, says Joyce O'Shaughnessy, who will present her findings Sunday at the American Society of Clinical Oncology meeting in Orlando.
Researchers are studying PARP inhibitors — available only in clinical trials — in a number of cancers, including breast, ovarian, uterine, brain and pancreatic tumors. But O'Shaughnessy says PARP inhibitors may work especially well in the 15% of breast cancer patients whose tumors don't respond to hormones or Herceptin.
Doctors are also studying the drugs in women such as Adler-Libstag who inherit a defect in a critical repair protein called BRCA1 or BRCA2, says O'Shaughnessy, of the Texas Oncology-Baylor Charles A. Sammons Cancer Center in Dallas.
Normally, these proteins fix damaged DNA. When these proteins don't work properly, people can accumulate mistakes in their DNA, leading to cancers of the breast and ovaries, O'Shaughnessy says.
One might expect that tumors like these would be easy to kill with chemotherapy. After all, tumors with malfunctioning BRCA protein can't perform their usual repairs.
Yet these cancers have a backup plan.
They turn to PARP, a repair enzyme that's abundant in cancer cells, says researcher Claudine Isaacs of Georgetown University's Lombardi Comprehensive Cancer Center. Because PARP is so good at cleaning up mistakes, it can help cancer cells survive — even after being poisoned by chemotherapy, Isaacs says.
Blocking PARP, however, is like taking away a race car's pit crew.
Isaacs says it's too soon to know how PARP inhibitors will affect healthy cells.
In her study, O'Shaughnessy will present early results in 86 of 120 patients. She plans to release more complete details in coming months.
Barbara Brenner of Breast Cancer Action, an advocacy group, cautions patients not to put too much faith in the results of early studies.
"It may turn out to be great, but let's finish the (larger) Phase 3 studies and find out," she says.
And Adler-Libstag, whose cancer has relapsed four times since she was diagnosed in 2004, knows she may not be cured. But a PARP inhibitor helped shrink her tumors, which now appear stable. And she says there are even rare times, when she's doing yoga, that she can forget that she has cancer.
"I'm either the luckiest unlucky person, or the unluckiest lucky person ever," Adler-Libstag says. "I can't figure that one out."
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