All study subjects experienced significant tumor shrinkage after just two months of treatment with a drug called a PARP inhibitor. Their tumors shrank anywhere from 30 to 98 percent, with a median reduction of 88 percent.
PARPs – short for Poly (ADP-ribose) polymerase – are proteins that can help different types of cells, including cancer cells, repair and survive damaged DNA. Inhibiting PARPs can keep cancer cells from surviving DNA damage and spreading.
“Acknowledging that this is a small study, I can’t think of any drug-based therapy that gives results this consistently strong in only two months,” says Jennifer Litton, M.D., associate professor of Breast Medical Oncology and leader of the study.
Now an extension of the original trial is underway, in which the PARP inhibitor talazoparib is given before any other treatment to newly diagnosed patients who also have BRCA genetic mutations which are associated with 5 to 10 percent of breast cancers and some ovarian cancers. BRCA-related cancers are thought to be vulnerable to PARP inhibitors. Currently, a chemotherapy combination followed by surgery is the frontline therapy.
In the initial trial, patients agreed to delay chemotherapy and first take talazoparib for two months, then proceed to chemotherapy and surgery. In the extension trial, patients are treated only with talazoparib before surgery.
“If the extension study produces strong results similar to those in the first trial,” Litton said, “the next step will be to directly compare talazoparib to chemotherapy in the presurgical, curative setting.”
Chemotherapy may even be delayed or replaced if the extension trial is similarly effective and shows less toxicity than the initial trial, she adds.
PARP inhibitors are approved by the Food and Drug Administration for advanced ovarian cancer, but are not yet approved for breast cancer.
Read more about this study in MD Anderson’s annual report.