Conference Coverage

PARP inhibitors and breast cancer: Questions remain about wider use



While poly (ADP-ribose) polymerase (PARP) inhibitors clearly show benefit in certain kinds of breast cancer, questions persist about ideal drug targets and the value of combining them with other medications, oncologists explained at the European Society for Medical Oncology Breast Cancer annual congress.

For now, the drugs are only approved in high-risk germline BRCA mutation (gBRCAmut) early breast cancer, oncologist Kevin Punie, MD, of Saint Augustine Hospital in Wilrijk, Belgium, said during a session at the meeting. Combining the drugs with chemotherapy “has not yet demonstrated significant benefits, and this is irrespective whether platinum was part of the chemotherapy backbone.”

PARP is a kind of enzyme that repairs damaged DNA in cells, especially cancerous ones. PARP inhibitors block the enzyme, potentially leading more cancer cells to die, the Dana-Farber Cancer Institute states.

In a separate presentation during the same session, oncologist Andrew Tutt, MBChB, PhD, noted that a study he led – a phase 3, double-blinded, randomized 2021 trial – found that patients with BRCA1- or BRCA2-mutated breast cancer who took the PARP inhibitor olarapib (Lynparza) versus placebo had improved outcomes on several measures, including 3-year invasive disease-free survival (85.9% vs. 77.1%, P < .001). However, the study noted that “olaparib had limited effects on global patient-reported quality of life.”

Dr. Tutt, of the Institute of Cancer Research, London, and Kings College London, said 57% of patients who took olarapib suffered nausea versus 24% of those who took placebo, and fatigue and anemia were also more common in the olarapib group. Anemia can be severe and lead to transfusions in some cases.

As Dr. Punie explained, there are many reasons to consider combining PARP inhibitors with other treatments such as chemotherapy, immunotherapy, and radiotherapy. The combinations may have synergetic effects, and they could have potential in both the neoadjuvant and adjuvant settings.

The combination of the PARP inhibitor olaparib and endocrine therapy is now approved by the European Medicines Agency for the adjuvant treatment of certain patients with germline BRCA1/2 mutations who have HER2-negative, high-risk early breast cancer, Dr. Punie noted.

The 2021 study led by Dr. Tutt reported that treatment or safety differences were found in those who received both olaparib and endocrine therapy versus those who only received olarapib.

So far, Dr. Punie said, “we not yet have enough clinical evidence to say that there’s really synergy between PNP inhibitors and other anticancer therapies.” According to the National Institutes of Health, medical synergy “describes the interaction of two or more drugs when their combined effect is greater than the sum of the effects seen when each drug is given alone.”

In regard to chemotherapy, it makes sense that PARP inhibitors would be helpful in combination, Dr. Punie said. DNA damage to cancer cells accumulates during chemotherapy, he said, and they’re more depending on PARP for repair.

Study results so far have been mixed. A 2022 study, for example, found that adding the experimental PARP inhibitor veliparib to the chemotherapy regimen carboplatin-paclitaxel didn’t improve outcomes, he said. A similar study examining the addition of olaparib to carboplatin-paclitaxel is ongoing.

As for combining radiotherapy and PARP inhibitors, Dr. Punie said that preclinical findings are promising, and research is underway. There’s also ongoing research into combining PARP inhibitors with immunotherapy.

Off-label use of olaparib with immunotherapy or sequential treatment may be appropriate in the setting of adjuvant gBRCAmut triple-negative breast cancer with residual disease, he said.

During his presentation, Dr. Tutt called for researchers to investigate the use of PARP inhibitors in the de-escalation of treatment in lower-risk gBRCAmut disease.

“Clearly, some patients require chemotherapy, and we know patients respond very well to neoadjuvant chemotherapy if they have a BRCA mutation, but we don’t yet know who we can de-escalate in,” he said.

He also highlighted the need to reduce anemia in patients on PARP inhibitors, “particularly if we’re moving into lower-risk populations or possibly considering prevention trials.

“The study of PARP inhibitor resistance ... is now urgent, so that we can address it,” he said.

Dr. Punie disclosed financial relationships with AstraZeneca, Eli Lilly, Exact Sciences, Focus Patient, Medscape, MSD, Mundi Pharma, Need, Novartis, Pierre Fabre, Pfizer, F. Hoffmann–La Roche, Sanofi, Seagen, and PharmaMar. Dr. Tutt disclosed financial relationships with Artios, Gilead, MD Anderson, Merck KGaA, Pfizer, Vertex, AstraZeneca, EM Partners, Medscape Education, CRUK, Inbiomotion, Myriad Genetics, and Breast Cancer Now.

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