Clinical Edge Journal Scan

Commentary: Combination Chemotherapies, September 2022

Dr. Abdou scans the journals so you don't have to!

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Yara Abdou, MD

The phase 3 KEYNOTE-355 study examined whether first-line treatment with pembrolizumab and chemotherapy improved outcomes in patients with advanced or metastatic triple-negative breast cancer (TNBC). A recent article by Cortes and colleagues presented the results of the updated and final overall survival (OS) analysis. A statistically significant OS benefit was demonstrated from the addition of pembrolizumab to chemotherapy in patients with previously untreated metastatic or unresectable TNBC whose tumors expressed programmed death ligand 1 (PD-L1) with a combined positive score (CPS) of ≥ 10 (median OS 23 months in the pembrolizumab-chemotherapy arm vs 16.1 months in the placebo arm; hazard ratio [HR] 0.73; 95% CI 0.55-0.95; P = .0185).

In the PD-L1 CPS ≥ 1 subgroup, however, no significant OS benefit was observed (median OS 17.6 months vs 16.0 months; HR 0.86; 95% CI 0.72-1.04; P = .1125). Additionally, in an exploratory analysis, the addition of pembrolizumab showed consistent OS benefit among patients whose tumors express PD-L1 with a CPS of 10-19 and CPS ≥ 20. The updated progression-free survival (PFS) and objective response rates (ORR) were consistent with prior interim data. No new safety signals were observed after the longer follow-up.

These data confirm that pembrolizumab plus chemotherapy should remain the first-line treatment for patients with advanced or metastatic TNBC whose tumors express PD-L1 with a CPS of ≥ 10. The treatment of metastatic TNBC with low or negative PD-L1 CPS scores remains an area of unmet clinical need, and further research is needed to explore better options for these patients.

Wang and colleagues presented results from a randomized, phase 3 trial comparing first-line nab-paclitaxel plus cisplatin (AP) with gemcitabine plus cisplatin (GP) among 254 patients with previously untreated metastatic TNBC. Median PFS (mPFS) was 9.8 months with AP vs 7.4 months with GP (HR 0.67; 95% CI 0.50-0.88; P  =  .004). Furthermore, AP had significantly higher ORR compared with GP (81.1% vs 56.3%; P  <  .001) and significantly improved median OS (26.3 months vs 22.9 months; HR 0.62; 95% CI 0.44-0.90; P  =  .010).

In the exploratory analyses of PFS by stratification factors, the mPFS was significantly longer in the AP group compared with the GP group in the majority of subgroups, except for those patients who presented with de novo stage IV disease or a disease-free interval of < 1 year. Regarding safety data, a significantly higher incidence of grade ≥ 3 neuropathy (19% vs 0%) and nausea and vomiting (6% vs 1%) was noted in the AP group compared with the GP group, while grade ≥ 3 thrombocytopenia was more common in the GP group compared with the AP group (29.4% vs 3.9%).

The AP doublet achieved superior efficacy with a manageable safety profile, compared with GP in patients with previously untreated metastatic TNBC. It is not clear, however, whether the AP doublet is superior to single-agent therapy in this setting, especially given several prior studies that showed no survival benefit and increased toxicity from combination therapy compared with sequential single-agent therapy in metastatic breast cancer. More studies are needed to establish the role of the AP doublet in combination with pembrolizumab in this cohort of patients, given that first-line pembrolizumab plus chemotherapy is considered the standard of care for patients with metastatic TNBC whose tumors express PD-L1.

Rugo and colleagues presented results from a randomized phase 3 study comparing 205 mg/m2 oral paclitaxel plus 15 mg encequidar (a novel P-glycoprotein pump inhibitor that allows oral absorption of paclitaxel) on 3 consecutive days per week vs 175 mg/m2 intravenous paclitaxel once every 3 weeks. The study enrolled 402 postmenopausal women from Latin America with metastatic breast cancer who were at least 1 year from their last taxane therapy. Oral paclitaxel plus encequidar (oPac + E) increased the confirmed tumor response compared with intravenous paclitaxel (IVpac) (36% vs 23%; P = .01). There was a trend toward improved PFS (8.4 vs 7.4 months; HR 0.768; 95.5% CI 0.584-1.01; P = .046) and OS (22.7 vs 16.5 months; HR 0.794; 95.5% CI 0.607-1.037; P = .08) with oPac + E compared to IVpac, respectively. Grade ≥3 adverse events were comparable with oPac + E and IVpac (55% vs 53%), although a lower incidence of grade 3 neuropathy (2% vs 15%) and alopecia (49% vs 62%) was noted with oPac + E compared with IVpac. A higher incidence of grade ≥ 3 gastrointestinal toxicity (nausea, vomiting, and diarrhea) and grade 4 neutropenic complications was noted in the oPac + E group. Patients with elevated baseline liver enzymes were particularly susceptible to early neutropenia and serious infections.

This study demonstrates that oral paclitaxel can be a possible alternative treatment option to intravenous paclitaxel in a select group of patients with metastatic breast cancer. High-grade neutropenia appears to be a major treatment-limiting toxicity with oPac + E. Therefore, careful patient selection and close monitoring are crucial for the successful management of this adverse event.

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