After every breast cancer patient responded positively to a new targeted therapy in a first-of-its-kind clinical trial, MD Anderson researchers have quickly taken the next step toward potentially establishing a new standard of care.
After just two months of treatment with a drug called a PARP inhibitor, tumors in all 13 newly diagnosed breast cancer patients shrank significantly.
Tumors shrank anywhere from 30% to 98% with a median reduction of 88% in the 13 patients studied.
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.
Litton originally expected the study would sign up 20 patients in two years. Instead, 13 enrolled in eight months, and the results were striking enough that the study was stopped in early 2016.
An extension of the study to enroll 20 more patients began in August, and is filling quickly.
The idea is to first give the PARP inhibitor talazoparib to newly diagnosed patients who also have BRCA mutations. BRCA-related cancers, including ovarian cancer, 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.
None of the 13 patients had to withdraw from the first trial due to side effects, which were limited mainly to fatigue and low blood counts. Eight of the 13 had triple-negative disease — a difficult-to-treat breast cancer that doesn’t have the cancer-promoting HER2 protein or two hormones (estrogen and progesterone) that fuel breast cancer growth and can be targeted by anticancer drugs.
“After we saw the extensive clinical response, confirmed by ultrasound, and with a favorable toxicity profile, we really wanted to move forward into an extension to evaluate this drug as a single treatment,” Litton says. “If the extension study produces similarly strong results, the next step would 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.
The Moon Shots Program is paving the way to faster results
In addition to the trials above, Litton is principal investigator of an international clinical trial of talazoparib for patients with advanced or metastatic breast cancer who have been previously treated.
To more quickly offer talazoparib to newly diagnosed patients who have not undergone surgery, Litton proposed an investigator-initiated pilot study backed by MD Anderson’s Moon Shots Program™. The pharmaceutical company that owns the drug agreed to the study. Litton noted that institutional support through the Moon Shots Program helped convince the company to provide the drug for her trials. Moon Shot™ backing decreased the time needed to launch the first trial by about two years, she estimates.
Extensive, unique biomarker research
The pilot and extension studies also tap Moon Shots Program resources for extensive biomarker evaluation, providing a unique opportunity for researchers and the drug company to better understand how the drug works and identify patients who will respond in advance.
Biopsies taken before and after PARP inhibition are evaluated for DNA and RNA changes, and proteomics (proteins) by Gordon Mills, M.D., Ph.D., chair and professor of Systems Biology.
Helen Piwnica-Worms, Ph.D., vice provost for science and professor of Experimental Radiation Oncology, and colleagues harvest tissue samples from patients’ tumors that can be transplanted into mice to further study how tumors respond to treatment.
“We will be able to learn a great deal,” Litton says.
“These models that are being built will be available for multiple investigators in the future to study and test other drugs and drug combinations.”