Michael Birrer, MD, PhD
The explosion of PARP inhibitors in ovarian cancer has provided new and exciting options for the treatment of patients, explains Michael Birrer, MD, PhD.
, Birrer, director, the University of Alabama at Birmingham Comprehensive Cancer Center, discussed the effect that PARP inhibitors have had on the treatment of ovarian cancer, and the potential for combinations with these agents.
OncLive: Can you discuss the impact that PARP inhibitors have had on the field?
: This is a new class of drugs, which most of us consider to be targeted therapy. It is perhaps not as targeted as EGFR inhibitors, but it is close. These are agents that inhibit the PARP protein and are fairly specific. The PARP protein is important because it is involved in single-stranded DNA repair. If you inhibit the ability of a cell to repair single-strand breaks, they become double-strand breaks, and double-strand breaks are lethal unless repaired. Double-strand breaks are repaired by BRCA1/2
. This is a great example of what is called synthetic lethality; it is very specific for cells that have homologous recombination deficiency (HRD), such as ovarian cancer, and it should not affect many other cells in the body. It is a very selective therapeutic approach.
PARP inhibitors have all the aspects of modern oncology—they are a form of targeted therapy, are associated with good biomarkers, have a great toxicity profile, and they come as a pill.
Which patients will benefit most from PARP inhibitor therapy?
There is a lot of level 1 evidence to tell us which patients will benefit the most. Level 1 means that it has been seen in randomized clinical trials. We now know that patients who benefit the most are patients who have either germline or somatic BRCA1/2
mutations. However, patients who have mutations in other genes within the Fanconi anemia pathway, possibly patients who have alterations of BRCA1/2
—not through mutation but through methylation or downregulation of the gene from microRNA— also benefit. It maybe will not be as much as BRCA1/2
mutations, but they still benefit.
Finally, these HRD assays have been developed that show a snapshot of the tumor in terms of the structure of its DNA. Therefore, [these assays] are looking at the loss of heterozygosity (LOH) patterns in the tumor cells. When there is a high degree of LOH, it is considered to be a surrogate for HRD.
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