Erin Roesch, MD
Program death-ligand 1 (PD-L1) inhibition suppresses tumor activity via modulation of immune and tumor cell interaction. TNBC is characterized by higher PD-L1 expression and increased immune infiltration, compared to other subtypes. In the randomized, phase 3 IMpassion130 trial, among 902 patients who were treatment naïve in the metastatic TNBC setting, an exploratory analysis in the PD-L1-positive population demonstrated a clinically meaningful OS benefit with atezolizumab + nab-paclitaxel compared to placebo + nab-paclitaxel (25.4 vs 17.9 months; HR 0.67) ( Emens et al ). Additionally, the phase 3 KEYNOTE-355 trial demonstrated PFS benefit among patients with mTNBC with combined positive score (CPS) ≥10 with pembrolizumab + chemotherapy (nab-paclitaxel, paclitaxel or gemcitabine/carboplatin) versus placebo + chemotherapy (mPFS 9.7 vs 5.6 months; HR 0.65, 95% CI 0.49-0.86). These results are in contrast to the phase 3 IMpassion131 trial which found no statistically significant difference in PFS or OS among 651 patients with mTNBC randomized to atezolizumab + paclitaxel vs placebo + paclitaxel (PD-L1-positive population: PFS 6.0 vs 5.7 months, HR 0.82, 95% CI 0.60-1.12; OS 22.1 vs 28.3 months, HR 1.11, 95% CI 0.76-1.62) ( Miles et al ). The reasons underlying these differences remain unclear and warrant further investigation. Some thoughts raised include lack of information on BRCA status (which may serve as prognostic factor) in IMpassion131, concomitant use of steroids with paclitaxel, and allowance of sufficient long-term follow-up for generation of events. Regardless, these studies suggest chemotherapy backbone is relevant and the regimens utilized in IMpassion130 and KEYNOTE-355 have gained FDA approval in the first-line mTNBC setting.
The phase 3 CLEOPATRA trial has established the regimen of docetaxel + trastuzumab + pertuzumab as standard of care in the first-line setting for metastatic HER2-positive breast cancer with an OS benefit of 16 months compared to docetaxel + trastuzumab + placebo (57.1 vs 40.8 months; HR 0.69, 95% CI 0.58-0.82) with over 8 years of follow-up. PERUSE was a single-arm phase 3b study that investigated the safety and efficacy of trastuzumab + pertuzumab combined with various taxanes (docetaxel, paclitaxel or nab-paclitaxel) among 1426 patients with HER2+ mBC ( Miles et al ). In the overall population at follow-up of 5.7 years, median PFS and OS were 20.7 and 65.3 months, respectively, and were similar regardless of taxane backbone. Docetaxel was associated with higher incidences of neutropenia and febrile neutropenia. These results support consideration of an alternative taxane combined with trastuzumab + pertuzumab in this setting (for example paclitaxel) in patients who may not be ideal candidates for docetaxel.
In the second-line treatment setting for HER2+ mBC with prior exposure to trastuzumab and taxane, the phase 3 EMILIA study showed improvement in OS with T-DM1 vs capecitabine + lapatinib (mOS 29.9 vs 25.9 months, HR 0.75, 95% CI 0.64-0.88). Ethier et al explored real-world application and outcomes associated with pertuzumab and T-DM1 in the first- and second-line settings respectively, in a population-based, retrospective cohort study in Ontario, Canada. In the pertuzumab cohort, median OS and time on treatment were 43 and 4 months, respectively. In the T-DM1 cohort, median OS and time on treatment were 15 months and 4 months, respectively. Additionally, patients in the T-DM1 cohort who were pertuzumab-naïve appeared to do better, potentially suggesting less responsiveness to subsequent HER2-targeted treatment in the real world setting among those who received prior pertuzumab. Findings from this population study demonstrate inferior outcomes when compared to the pivotal CLEOPATRA and EMILIA trials, and highlight a gap between clinical trial and real-world observations (described by authors as efficacy-effectiveness gap). Potential etiologies for these differences include patient factors, prior therapies and delivery of care models, and convey the importance of recognizing this gap exists and optimizing any modifiable factors as trial data and novel therapies are applied to routine clinical practice.
References:
Mittendorf EA, Philips AV, Meric-Bernstam F, et al. PD-L1 expression in triple-negative breast cancer. Cancer Immunol Res. 2014;2(4):361-70.
Cortes J, Cescon DW, Rugo HS, et al. Pembrolizumab plus chemotherapy versus placebo plus chemotherapy for previously untreated locally recurrent inoperable or metastatic triple-negative breast cancer (KEYNOTE-355): a randomised, placebo-controlled, double-blind, phase 3 clinical trial. Lancet. 2020;396(10265):1817-1828.
Swain SM, Miles D, Kim SB, et al. Pertuzumab, trastuzumab, and docetaxel for HER2-positive metastatic breast cancer (CLEOPATRA): end-of-study results from a double-blind, randomised, placebo-controlled, phase 3 study. Lancet Oncol. 2020;21(4):519-530.
Diéras V, Miles D, Verma S, et al. Trastuzumab emtansine versus capecitabine plus lapatinib in patients with previously treated HER2-positive advanced breast cancer (EMILIA): a descriptive analysis of final overall survival results from a randomised, open-label, phase 3 trial. Lancet Oncol. 2017;18(6):732-742.