medwireNews: Adding atezolizumab to paclitaxel does not improve progression-free survival (PFS) or overall survival (OS) in patients with unresectable locally advanced or metastatic triple-negative breast cancer (TNBC), IMpassion131 data show.
The findings presented at the ESMO Virtual Congress 2020 are in contrast to those of the IMpassion130 study, which was also reported at the virtual congress and had a similar design to IMpassion131 but used nab-paclitaxel instead of paclitaxel.
David Miles (Mount Vernon Cancer Centre, Northwood, UK) told delegates that the potential reasons for the contrast between the two trials “require further exploration.”
Leisha Emens summarizes the IMpassion130 trial and comments on the differences with the IMpassion131 study (2:19)
In the phase 3 IMpassion131 trial, 651 patients with TNBC were randomly assigned to receive atezolizumab 840 mg (n=220) or placebo (n=431) on days 1 and 15 of each 28-day cycle, both in combination with paclitaxel 90 mg/m2 on days 1, 8, and 15 as a first-line treatment for metastatic disease until disease progression or unacceptable toxicity.
Miles reported that, among the 292 patients who were positive for PD-L1 expression, PFS was 6.0 months with atezolizumab and 5.7 months without, a nonsignificant difference. In the intention-to-treat (ITT) population, PFS was 5.7 months and 5.6 months, respectively.
There was also no significant difference between the atezolizumab and placebo arms in objective response rate in either the PD-L1-positive (63.4 vs 55.4%) or ITT (53.6% vs 47.5%) populations.
The interim overall survival (OS) data triggered a safety alert for the combination treatment, as previously reported by medwireNews, and led the researchers to perform a more detailed analysis of the survival data.
In this updated analysis, occurring after 47% of the ITT population had died, the estimated 2-year OS rates were 49% with atezolizumab and 51% with placebo in the PD-L1-positive population and 42% and 45%, respectively, in the ITT population. The resulting nonsignificant hazard ratios (HRs) for death were a respective 1.12 and 1.11, with wide confidence intervals, Miles said.
He also noted that that these HRs were lower than those observed in the interim analysis (1.55 and 1.31, respectively) and “this gives us some confidence that we are not seeing an adverse effect in the atezolizumab arm.”
Given the survival results, the researchers explored whether delivery of chemotherapy was compromised by use of atezolizumab or if toxicity was an issue.
However, they found that median dose paclitaxel intensities and cumulative doses were similar between the two arms, and no new safety signals were seen.
The findings of both IMpassion131 and IMpassion130 were discussed by Lisa Carey, from the Lineberger Comprehensive Cancer Center in Chapel Hill, North Carolina, USA.
She said that the differing results could be a result of the different chemotherapy agents used but could also be a “play of chance,” noting that the confidence intervals for the HR for PFS in IMpassion131 overlapped with those in IMpassion130.
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