Olaparib in metastatic breast cancer accompanied by germline PALB2 mutations: 2 case reports

Introduction We present two cases with metastatic breast cancer (mBC) and germline PALB2 ( gPALB2 ) mutation who were treated with the poly(adenosine diphosphate-ribose) polymerase (PARP) inhibitor olaparib under off-label palliative settings. Methods Case 1 experienced relapse in the mediastinal lymph node which was hormone-receptor positive (HR+), human epidermal growth factor receptor 2 negative (HER2-), gBRCA negative ( gBRCA -), three years after initial diagnosis. Following identification of a gPALB2 mutation by next-generation sequencing (NGS), patient was initiated on olaparib, 600 mg/day (subsequently reduced to 200 mg/day). Case 2 experienced relapse in the liver which was HR+, HER2-, gBRCA -, 10 years after initial diagnosis. Following identification of a gPALB2 mutation, patient was initiated on olaparib, 600 mg/day. Results In Case 1, substantial reduction in tumour marker CA 15-3 was evident by month 3. PET/CT scans at month 7 revealed regression of lesions corresponding to partial response (RECIST v1.1 criteria). Patient received olaparib for 16 months till disease progression after which olaparib was discontinued and patient was lost to follow-up. In Case 2, stable disease was observed for 7 months before disease progression at which point olaparib was discontinued. Case 2 died eight months thereafter. Conclusions PARP inhibitors could have beneficial effects in mBC with gPALB2 mutations thus highlighting the need to identify this subset of patients through early NGS. Olaparib needs to be investigated in larger clinical trials on mBC patients with gPALB2 variants. Publication History Article published online: 01 June 2021 © 2021. Thieme. All rights reserved. Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany