3. Only offer poly (ADP-ribose) polymerase (PARP) inhibitors plus radiotherapy in clinical trial setting
PARP inhibitors olaparib (Lynparza) and talazoprib (Talzenna) are standard of care in patients with metastatic breast cancer who have BRCA1/2 gene mutations. Olaparib is also indicated for high-risk early breast cancer following neoadjuvant or adjuvant chemotherapy.
But data on combining PARP inhibitors with radiotherapy in breast cancer also remain limited.
One ongoing phase 2 trial, comparing olaparib plus radiotherapy to radiotherapy alone in 300 people with inflammatory breast cancer, is aiming to tease out the safety of the combination and whether it improves local control in patients with aggressive disease.
“The desire is to explore the exciting possibility that low doses of PARP inhibition may radiosensitize tumor cells more than normal tissues,” Reshma Jagsi, MD, chair of the Department of Radiation Oncology at Emory University School of Medicine in Atlanta, Georgia, who is leading the study.
Because of potential good or bad interactions between new systemic therapies and radiotherapy, “intentional trial design” is important, Dr. Jagsi said, so we “know the best way to combine treatments in practice to optimize outcomes.”
But given the evidence to date, the ESTRO experts advised waiting until “further research provides more comprehensive safety and efficacy data” in the primary, adjuvant, and metastatic settings. The experts also advised not offering PARP inhibitors and concomitant radiotherapy to treat advanced breast cancer outside of clinical trials.
4. Phosphoinositide 3-kinase inhibitors (PI3K) inhibitors, mammalian target of rapamycin (mTOR) inhibitors, and newer targeted agents should not be offered concurrently with radiotherapy
Clinical trial data on the safety of combining PI3K and mTOR inhibitors with radiation are thin, especially in advanced breast cancer. Typically, radiotherapy within 4 weeks before randomization, or 2 weeks for palliative radiation, was excluded in pivotal trials.
For this reason, the ESTRO team recommended that concurrent radiation with either PI3K inhibitors or mTOR inhibitors “should not be offered.”
ESTRO also cautioned against providing radiation concurrently with newer anti-HER2 tyrosine-kinase drugs, such as neratinib or tucatinib, or newer antibody-drug conjugates such as trastuzumab deruxtecan, until more data emerge on the safety of these combinations.
5. Combining older HER2-targeted drugs and radiotherapy generally safe
The ESTRO authors agreed that older anti-HER2 drugs trastuzumab (Herceptin), pertuzumab (Perjeta), and lapatinib (Tykerb) can be safely used concurrently with locoregional radiotherapy as well.
One of the biggest concerns in the field is how to combine radiation with systemic therapies in the setting of brain metastases, and the data on these older anti-HER2 drugs are relatively clear that it’s safe, Dr. Miller said.
For instance, in a 2019 study of 84 patients with 487 brain metastases, stereotactic radiosurgery given alongside lapatinib led to significantly higher rates of complete responses than stereotactic radiosurgery alone (35% vs 11%) with no increased risk for radiation necrosis.
The ESTRO team agreed, noting that the latest evidence supports the use of trastuzumab, pertuzumab, or lapatinib alongside radiotherapy for whole brain and ablative intracranial stereotactic radiotherapy.
As for older antibody-drug conjugates, trastuzumab emtansine (T-DM1) plus radiotherapy “might be considered” during adjuvant locoregional radiotherapy for breast cancer but should not be offered for whole brain and ablative intracranial stereotactic radiotherapy, the ESTRO team said.
Dr. Jagsi declared the following conflicts in a recent 2024 publication: Stock options for advisory board role in Equity Quotient; grants or contracts from Genentech; and expert witness for Kleinbard, LLC, and Hawks Quindel Law. In the Keynote-522 trial publication Dr. Schmid declared relationships with AstraZeneca, Bayer, Boehringer Ingelheim, Celgene, Eisai, Hoffmann-La Roche, Genetech, Merck, Novartis, and Pfizer. Dr. Shah reported consulting for Impedimed, Videra Surgical, and PreludeDX.
A version of this article appeared on Medscape.com.