Exposure-Safety Analyses of Talazoparib in Patients With Advanced Breast Cancer and Germline BRCA1/2 Mutations in the EMBRACA and ABRAZO Trials

Poly(ADP-ribose) polymerase inhibitors, such as talazoparib, may affect hematopoiesis. This analysis characterized the relationship between talazoparib exposure and the most common grade ≥ 3 hematopoietic adverse events (AEs) leading to dose modification in the phase 2 (ABRAZO) and phase 3 (EMBRACA) trials. The relationship between time-varying average talazoparib concentration (C_avg,t ), along with other baseline variables, and grade ≥ 3 anemia, thrombocytopenia, and neutropenia were evaluated both by graphical examination and using univariate and multivariate Cox proportional hazard models. The results indicated that higher C_avg,t was associated with a higher risk of anemia and thrombocytopenia. A trend toward an association between higher C_avg,t and neutropenia was observed, although not statistically significant. Higher risk of all tested safety end points was associated with lower baseline hemoglobin. Higher risk of neutropenia was associated with lower baseline absolute neutrophil count and lower body weight. These findings support the proposed management of AEs through talazoparib dosing modification.

Talazoparib Exposure-Efficacy Analysis in Patients With Advanced Breast Cancer and Germline BRCA1/2 Mutations in the EMBRACA Trial

In the phase 3 EMBRACA trial, treatment with the poly(ADP-ribose) polymerase inhibitor, talazoparib, led to significantly improved progression-free survival (PFS) compared with chemotherapy (hazard ratio, 0.54; 95% confidence interval, 0.41-0.71; P < .0001). We conducted an exposure-efficacy analysis using EMBRACA data from 285 patients who were treated with talazoparib and had available pharmacokinetic parameters to evaluate the effect of talazoparib exposure (time-varying average talazoparib concentration [C_avg,t ]) and other baseline variables on PFS. Graphical examination of the relationship between C_avg,t and PFS and a Cox proportional model were used. Exposure-response analyses showed that higher talazoparib exposure, absence of visceral disease, lower baseline lactate dehydrogenase levels, and disease-free interval >12 months were independent covariates associated with longer PFS. The association of talazoparib exposure with PFS (higher exposure, longer PFS) suggests the recommended starting dose of 1 mg once daily (the maximum tolerated dose) is appropriate.

Talazoparib: First Global Approval

Talazoparib (TALZENNA™) is an oral inhibitor of the polyadenosine 5'-diphosphoribose polymerase (PARP) enzymes, which play a critical role in repairing DNA single-strand breaks. It has been developed by Pfizer and was recently approved in the USA for the treatment of adults with deleterious or suspected deleterious germline BRCA-mutated, human epidermal growth factor receptor 2 (HER2)-negative, locally advanced or metastatic breast cancer (as detected by a US FDA-approved assay). A regulatory assessment for talazoparib in this patient population is underway in the EU, with talazoparib also undergoing development for use in metastatic castration-resistant prostate cancer and various solid tumours, and as neoadjuvant therapy in early triple negative breast cancer. This article summarizes the milestones in the development of talazoparib leading to its first approval for the treatment of adults with deleterious or suspected deleterious germline BRCA-mutated, HER2-negative, locally advanced or metastatic breast cancer.