Combining a new drug with standard chemo delivers a one-two punch against a virulent type of breast cancer, according to new research out of the Perelman School of Medicine at the University of Pennsylvania.

In a study presented at the 2015 San Antonio Breast Cancer Symposium, investigators reported a combo therapy using the new breast cancer drug palbociclib with paclitaxel (Taxol) shrank tumors in nearly half of patient with estrogen-receptor (ER) positive breast cancer.

A second study offered new clues to how breast cancer develops resistance to the palbociclib, a common occurrence among many patients who take the drug.

"Results of the first study found that palbociclib and paclitaxel can be safely combined on an alternating dosing schedule," said Dr. Angela DeMichele, an associate professor at Penn who helped conduct the study. "The high response rate we saw suggests this combination may hold benefits for patients over paclitaxel alone. Based on these results, a larger clinical trial to determine the benefits is warranted."

Palbociclib targets tumor cells blocks their growth and development, while paclitaxel kills cells as they divide. As a result palbociclib effectively makes cancer cells more vulnerable to paclitaxel.
The team’s findings are based on the results of treatment involving 27 breast cancer patients who were given alternating doses of palbociclib and paclitaxel.

Although the trial wasn't designed to test whether the combo is more effective than paclitaxel alone, the patients' responses were promising, with nearly half showed long-term shrinkage or disappearance of tumors.

"That seemed better than what we would have expected from paclitaxel alone, but the only way to know the difference for certain is with a randomized clinical trial of the combination versus the single drug," DeMichele said.

The team now hopes to conduct a clinical study and another newly developed drug, Novartis's ribociclib.