PARP Inhibitor Olaparib Has Activity in High-Grade Serous Ovarian Cancer Without Inherited BRCA1 or BRCA2 Gene Mutations

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Researchers affiliated with the British Columbia Cancer Agency reported Phase 2 clinical study results indicating that advanced ovarian cancer, with and without germline (inherited) BRCA 1 or BRCA 2 gene mutations, responded to treatment with the PARP inhibitor olaparib. The Phase 2 study results were published online in the August 21 edition of The Lancet Oncology.

Karen A. Gelmon, M.D., Lead Study Author, Medical Oncologist, and Head of the Investigational Drug Program, Experimental Therapeutics, Department of Medical Oncology, British Columbia Cancer Agency

Researchers affiliated with the British Columbia Cancer Agency reported results from a Phase 2 clinical study indicating that advanced ovarian cancer, with and without germline (inherited) BRCA 1 or BRCA 2 gene mutations, responded to treatment with the PARP (poly(ADP-ribose) polymerase ) inhibitor olaparib (a/k/a AZD2281).[1] The Phase 2 study results were published online in the August 21 edition of the Lancet Oncology.

Preliminary findings from this study were reported at the 2011 American Society of Clinical Oncology annual meeting, which was held in Chicago earlier this year. [2]

The Phase 2 study results indicate that approximately 41% of women with BRCA1 or BRCA 2-mutated ovarian cancer had objective responses to the targeted agent, along with 24% of patients with non-BRCA gene mutated ovarian cancer. The findings suggest that the PARP inhibitor olaparib might have broad applicability in ovarian cancer.

Unfortunately, the drug olaparib failed to produce any objective responses in patients with non-BRCA gene mutated, triple negative breast cancer. Triple negative breast cancer is a difficult to treat subtype of the disease that lacks three of the cellular “receptors” known to fuel most breast cancers: estrogen receptors, progesterone receptors, and human epidermal growth factor receptor 2 (HER2).

Background

Olaparib is a small-molecule, potent oral PARP inhibitor. Olaparib targets PARP, an enzyme essential for repair of single-strand DNA breaks. Preclinical evidence showed that the drug olaparib had activity against tumors with homologous recombination (HR) DNA repair defects, such as those caused by BRCA 1 or BRCA 2 gene mutations.

Germline (inherited) BRCA 1 or BRCA 2 gene mutations confer a high risk of breast and ovarian cancers, and tumors arising from the mutations have aggressive tendencies, such as triple-negative breast cancer. PARP inhibition has already demonstrated activity in cancers with germline mutations. Accordingly, the goal of the Canadian researchers was to assess the safety and tolerability of this drug in patients with advanced triple-negative breast cancer or high-grade serous and/or undifferentiated ovarian cancer, which did not possess BRCA1 or BRCA2 mutations.

Past study reporting associated with olaparib over the past twelve months has been somewhat mixed. Data reported at the 2010 European Society of Medical Oncology annual congress showed no significant effect of olaparib on progression-free survival (PFS) in women with advanced BRCA gene-mutated ovarian cancer. [3] In contrast, data presented at the 2011 American Society of Clinical Oncology meeting showed almost a doubling of PFS with olaparib among women with relapsed, platinum-sensitive ovarian cancer. [4]

Olaparib Phase 2 Study Design

The olaparib Phase 2 study enrolled women into 4 cohorts or trial arms. The two stage trial design included:

  • BRCA 1 or BRCA 2 gene mutation negative (or unknown mutation status) patients with high-grade serous, undifferentiated, fallopian-tube, or primary peritoneal cancer (Arm A) or triple-negative breast cancer (Arm B); and
  • Two reference groups with recurrent ovarian cancer (Arm C) or breast cancer (Arm D) who possessed BRCA 1 or BRCA 2 gene mutations.

All patients had tumor biopsies taken prior to treatment, after 2 cycles of treatment, and at disease progression to assess PARP inhibitor activity, loss of heterozygosity, gene mutational changes, BRCA 1 or BRCA 2 gene expression, and other markers of response. Computed tomography (CT)/magnetic ressonance imaging (MRI) assessments were performed prior to treatment and at every 2 treatment cycles. The patients were treated with single agent olaparib (400 mg twice a day) on a continuous basis in 4 week cycles.

Researchers at six centers in Canada enrolled 91 patients in this Phase 2, open-label, nonrandomized trial (ClinicalTrials.gov ID: NCT00679783). [5] Eligible patients had advanced metastatic or recurrent breast cancer, or advanced ovarian cancer.

The study population consisted of 65 patients with ovarian cancer and 26 patients with breast cancer. All of the breast cancer patients and 64 ovarian cancer patients received at least one dose of olaparib (400 mg twice a day) and were included in the final study analysis.

The ovarian cancer cohort consisted of 17 patients with BRCA gene mutations and 47 patients without BRCA gene mutations. The breast cancer cohort consisted of 10 patients with BRCA gene mutations and 16 patients without BRCA gene mutations.

The researchers reported that 58 patients with ovarian cancer had the serous subtype (13 patients with BRCA gene mutations, 45 patients without BRCA gene mutations). In the breast cancer cohort, 21 patients had triple-negative disease, including five patients with BRCA gene mutations.

The primary endpoint of the Phase 2 study was objective response, as determined by RECIST (Response Evaluation Criteria In Solid Tumors) criteria.

Olaparib Phase 2 Study Results

None of the breast cancer patients had objective responses, and the disease control rate (proportion of patients with complete response, partial response, or stable disease) at eight weeks was 38% (10 of 26 patients).

In the ovarian cancer cohort, seven of 17 (41%) patients with BRCA gene mutations, and 11 of 46 (24%) patients without BRCA gene mutations, experienced objective responses. The overall disease control rate was 66% (42 of 64), including benefit in 76% (11 of 17) of BRCA-negative patients and 62% (29 of 47) of the BRCA-positive subgroup.

The researchers reported: “Although responses were seen in both platinum-sensitive and platinum-resistant populations, our post hoc analysis reported activity mostly in patients with platinum-sensitive disease.” As a precaution, the researchers noted that their findings should be interpreted conservatively because of the small study sample size.

Among the ovarian cancer patients, there were thirteen premature discontinuations, without confirmed radiological disease progression. Six patients dropped out of the Phase 2 olaparib study. Of those patients, three women dropped out because of worsening disease, and three more women dropped out because of adverse events. One patient in the breast cancer group discontinued early because of an adverse event.

The most common adverse events in ovarian and breast cancer patients were fatigue (58 patients), nausea (58), vomiting (34), and decreased appetite (30).

“To our knowledge, this study is the first to show that olaparib monotherapy has activity in women with pretreated high-grade serous ovarian cancer without germline BRCA1 or BRCA2 mutations,” said Karen A. Gelmon, M.D., lead study author, medical oncologist, and head of the Investigational Drug Program, Experimental Therapeutics, within the department of medical oncology of the British Columbia Cancer Agency, along with her co-authors. Dr. Gelmon is also a professor of  medicine at the University of British Columbia.

“New treatments targeting DNA repair mechanisms seem to provide new hope for treatment of ovarian cancer,” the Canadian researchers added. “Subsequent reports of this study assessing tumor biopsies might identify which patients obtain most clinical benefit from olaparib.”

Expert Commentary

Melinda Telli, M.D., Assistant Professor, Stanford School of Medicine, Stanford University

The study findings by Gelmon et al. were accompanied by a commentary which was written by Melinda L. Telli, M.D., assistant professor, Stanford School of Medicine. [6] In that commentary, Dr. Telli states:

… Their [Gelson et al.] study is noteworthy in that it shows, for the first time, activity of a PARP inhibitor as monotherapy in women with advanced high-grade serous ovarian cancer who do not have a germline BRCA1 or BRCA2 mutation. This finding not only suggests new therapeutic possibilities for women with this aggressive type of ovarian cancer, but also importantly confirms the hypothesis that subpopulations of patients with common sporadic tumors can be targeted effectively with PARP inhibitor therapy. An additional important negative finding of this study was the absence of objective responses to single-agent olaparib in women with sporadic triple-negative breast cancer, although the numbers were small and patients heavily pretreated. With new therapies come new challenges, and the clinical development of PARP inhibitors has certainly encountered many obstacles. Thus, to see the potential of these drugs realized is particularly satisfying. This important finding of activity in high-grade serous ovarian cancer marks a new beginning to what will hopefully be a long and fruitful future for PARP inhibitors as they make their move beyond BRCA.

Another expert expressed excitement about the future potential of olaparib. Stephanie V. Blank, M.D., an assistant professor in clinical gynecologic oncology at NYU School of Medicine, said:

It is extremely exciting that an agent as promising as olaparib can be effective in a broader group of women than had been expected. The next challenge will lie in getting our hands on the drug, which at present is only available for patients on clinical trials.

Study Relationship Disclosures

The study was supported by AstraZeneca. Gelmon and several co-authors disclosed relationships with AstraZeneca. The co-authors included AstraZeneca employees. Dr. Telli reported no relevant disclosures.

Libby’s H*O*P*E* Commentary

We would like to extend our congratulations to Dr. Gelmon, as well as her co-investigators, many of whom are critical team members of  the Ovarian Cancer Research Program of British Columbia (OvCaRe). On September 8, 2010, we reported on the OvCaRe team finding of prevalent ARID1A gene mutations in endometriosis-associated, epithelial ovarian cancers (i.e., clear cell and endometrioid). [7]

The findings reported by Gelmon et al. will take on critical importance if it is eventually proven that PARP inhibitors could benefit up to 50% of high-grade serous ovarian cancer patients who possess germline (inherited) or somatic (lifetime acquired) mutations in the BRCA 1 or BRCA 2 gene, or other alternations in the HR DNA repair pathway, as suggested by past preclinical study findings, [8] including those recently reported by The Cancer Genome Atlas. [9]

References

1/ Gelmon KA, et al. Olaparib in patients with recurrent high-grade serous or poorly differentiated ovarian carcinoma or triple-negative breast cancer: A phase II, multicenter, open-label, nonrandomized study. Lancet Oncol 2011; 12: 852-861. [Abstract]

2/Gelmon KA, et al. Can we define tumors that will respond to PARP inhibitors? A phase II correlative study of olaparib in advanced serous ovarian cancer and triple-negative breast cancer. J Clin Oncol 28:15s, 2010 (suppl; abstr 3002) [2011 American Society of Clinical Oncology Annual Meeting, Abstract 3002]

3/Kaye S, et al Phase II study of the oral PARP inhibitor olaparib (AZD2281) versus liposomal doxorubicin in ovarian cancer patients with BRCA1 and/or BRCA2 mutations. Annals of Oncology 2010 21(8)8): viii304–viii313, 2010 doi:10.1093/annonc/mdq526 [2010 European Society of Medical Oncology Annual Meeting, Abstract 9710, Adobe Reader PDF Document].

4/Ledermann JA, et al. Phase II randomized placebo-controlled study of olaparib (AZD2281) in patients with platinum-sensitive relapsed serous ovarian cancer (PSR SOC). J Clin Oncol 29: 2011 (suppl; abstr 5003) [2011 American Society of Clinical Oncology Annual Meeting, Abstract 5003]

5/Phase II, Open Label, Non-Randomized Study of AZD2281 in the Treatment of Patients With Known BRCA or Recurrent High Grade Serous/ Undifferentiated Tubo-Ovarian Carcinoma and in Known BRCA or Triple Negative Breast Cancer to Determine Response Rate and Correlative Markers of Response, ClinicalTrials.gov ID: NCT00679783.

6/Telli ML. PARP inhibitors in cancer: Moving beyond BRCA. Lancet Oncol 2011; 12: 827-828. [Full Text]

7/British Columbian Researchers Make Groundbreaking Genetic Discovery In Endometriosis-Associated Ovarian Cancers, by Paul Cacciatore, Libby’s H*O*P*E*™, September 8, 2010.

8/New Assay Test Predicts That 50% of Ovarian Cancers Will Respond To In Vitro PARP Inhibition, by Paul Cacciatore, Libby’s H*O*P*E*™, November 11, 2010.

9/In-Depth Review: The Cancer Genome Atlas Reports On Landmark Analysis of High-Grade Serous Ovarian Cancer, by Paul Cacciatore, Libby’s H*O*P*E*™, August 5, 2011.

Additional Sources:

PARP Inhibitor Clinical Trial Information

Related Libby’s H*O*P*E* Posts

  • Inherited Mutations in RAD51D Gene Confer Susceptibility to Ovarian Cancer, August 7, 2011.
  • In-Depth Review: The Cancer Genome Atlas Reports On Landmark Analysis of High-Grade Serous Ovarian Cancer, August 5, 2011.
  • ASCO 2011: Maintenance Therapy With PARP Inhibitors Could Play Important Role in Treatment of Recurrent Ovarian Cancer, May 19, 2011.
  • PARP Inhibitor MK-4827 Shows Anti-Tumor Activity in First Human Clinical Study, November 17, 2010.
  • New Assay Test Predicts That 50% of Ovarian Cancers Will Respond To In Vitro PARP Inhibition, November 11, 2010.
  • PARP Inhibitor Olaparib Benefits Women With Inherited Ovarian Cancer Based Upon Platinum Drug Sensitivity, April 23, 2010.

Related WORD of HOPE Ovarian Cancer Podcast

  • 10 Exciting Ovarian Cancer Research Topics from 2010 — PARP Inhibitors & BRCA Gene-Mutated Ovarian Cancer (Topic #2 of 10), Episode #2, WORD of HOPE Ovarian Cancer Podcast, April 11, 2011.

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