Researchers at Penn State University have said that a novel therapy has the potential to slow tumour growth in advanced breast cancer.
Researchers found that the revolutionary therapy, designed to attack tumours in patients with a genetic mutation in either BRCA1 or BRCA2, slowed tumour growth in 85 percent of advanced breast cancer patients treated in a small study.
"That is really an enormous response rate in a population of patients who have received a median of three prior therapies," Lancet quoted study co-author Dr. Susan M. Domchek, as saying.
"This is the first time that we have been able to take the genetic reason a person has developed cancer and make it a target. Most of the time we look at what is going on in the tumor itself and then figure out how to target it. But in this situation, the women all had an inherited mutation in either the BRCA1 or BRCA2 gene and we could exploit that weakness in the tumour. It is a strategy that may cause fewer side effects for patients," said Domchek. "
The new agent, called olaparib, inhibits a protein called poly(ADP-ribose) polymerase (PARP).
Both PARP and the BRCA proteins are involved in DNA repair. And while cells seem to be able to do without one or the other, inhibiting PARP in a tumour that lacks a BRCA gene is too much for the cells, and causes them to die.
"If you put too much stress on the cancer cell, it can't take it and it falls apart," said Domchek.
Because the non-tumour cells in a patient with an inherited BRCA mutation still retain one normal copy of the BRCA gene, they are relatively unaffected by PARP inhibition.
"These drugs may be very potent in tumour cells and much less toxic in normal cells. That is important from the perspective of cancer treatment," said Domchek.
Although the results look good thus far, Domchek said more clinical trials will be necessary before olaparib or other PARP inhibitors in development will be ready for use in regular practice.
"It is important for patients to join those clinical trials because we need to determine how best to use these drugs, on their own or in combination with other agents. And we need to establish definitively that they are better than other drugs," she said.
The PARP inhibitors are a transition in the field of cancer drug development.
"This is a different way of looking at cancer therapeutics. In oncology, this is really one of the first times that we've seen drugs being developed on the basis of inherited susceptibility - and that may open up a whole new avenue of drug development," said Domchek.
The study is published in the latest issue of the Lancet.