Is it time to expand the use of PARP inhibitors?
Advanced ovarian cancer
The randomized, double-blind, placebo-controlled, phase 3 PAOLA-1/ENGOT-ov25 trial studied patients with stage III-IV ovarian, fallopian tube, or primary peritoneal cancer who had surgery, platinum-taxane chemotherapy, and at least 3 months of bevacizumab. Patients were randomized to maintenance treatment with an additional 12 months of bevacizumab plus 24 months of PARPi with olaparib or placebo. Germline BRCA mutations were not required (Ray-Coquard I et al. ESMO 2019, Abstract LBA2).
As reported at ESMO, adding PARPi to bevacizumab maintenance provided a clinically meaningful PFS benefit of 22.1 months, in comparison with 16.6 months for bevacizumab alone. The difference was statistically significant.
For patients with tumor BRCA mutations (tBRCAm), PFS was 37.2 months with olaparib vs. 21.7 months for placebo (HR, 0.31). The PFS benefit was even more impressive for homologous recombination deficient (HRD)–positive patients, inclusive of those with tBRCAm (PFS 37.2 months for PARPi vs. 17.7 months for placebo; and in the 152 HRD-positive patients without tBRCAm, (median PFS 28.1 months vs. 16.6 months; HR, 0.43).
The improved PFS in patients with tBRCAm is similar to that reported in the SOLO1 trial of olaparib monotherapy vs. chemotherapy in newly diagnosed advanced ovarian cancer (N Engl J Med. 2018; 379:2495-2505), but the PFS in the control arm was longer in PAOLA-1 than in SOLO1, perhaps because of the use of bevacizumab in PAOLA-1. PARPi did not affect tolerance to bevacizumab.
In PAOLA-1, the HRD-positive patients who lacked tBRCAm and, by extension, lacked germline BRCA mutations – a new population of patients – was identified who benefited substantially from maintenance PARPi in the first-line setting.
What this means in practice
PAOLA-1 demonstrates that PARPi can improve outcomes in first-line treatment – and in patients beyond those with germline BRCA mutations. As a result, PAOLA-1 potentially changes the standard of care for initial treatment of the respectable fraction of patients with previously untreated, advanced müllerian cancers who have either tBRCAm or HRD positive tumors.
Importantly, PAOLA-1 is one of many published trials that stimulates the discussion of cost vs. value for combinations of biologics. The incremental benefit from the second biologic (in this case PARPi) is almost never completely additive or supra-additive to the benefit associated with the first biologic (in this case, bevacizumab). In that regard, despite the fact that PARPi showed a PFS benefit in the intent-to-treat population overall, precisely defining the patient population that has the greatest benefit will facilitate the goal of getting the treatments of greatest “value for cost” to our patients in the most responsible way.
Additional research will hopefully define the relative contribution of bevacizumab to PARPi in patients who benefited so dramatically from PARPi in PAOLA-1.
Dr. Lyss has been a community-based medical oncologist and clinical researcher for more than 35 years, practicing in St. Louis. His clinical and research interests are in the prevention, diagnosis, and treatment of breast and lung cancers and in expanding access to clinical trials to medically underserved populations.
