COMMENTARY

The Possibilities of Pembrolizumab Plus Chemo in Breast Cancer Treatment

Alan P. Lyss, MD

Disclosures

March 12, 2020

In this edition of "applying research to practice," I'm highlighting I-SPY2 and other studies of pembrolizumab plus chemotherapy in breast cancer patients.

裸艺Alan P. Lyss, MD

Pathologic complete response (pCR) rates up to 60% were reported for patients with high-risk, stage II/III breast cancer who received pembrolizumab plus standard neoadjuvant chemotherapy (NAC) in , an ongoing platform trial designed to screen multiple agents and pinpoint those with a high probability of success.

The addition of pembrolizumab to NAC doubled pCR rates in all three biomarker signatures studied, including ERBB2 (HER2)-negative, hormone receptor (HR)-positive/ERBB2-negative, and triple-negative breast cancer (TNBC).

As a result, pembrolizumab "graduated" from I-SPY2, with a more than 99% predictive probability that the pembrolizumab-plus-NAC approach would be superior to NAC alone in a phase 3 trial. In the HR-positive/ERBB2-negative signature, pembrolizumab is the first agent to graduate among the 10 agents studied since I-SPY2 opened in 2010.

The control arm in I-SPY2 had 181 patients randomly assigned to standard NAC (paclitaxel followed by doxorubicin plus cyclophosphamide). The pembrolizumab arm included 69 patients who received the same NAC regimen plus pembrolizumab, given concurrently with paclitaxel.

裸艺The estimated pCR rates in all ERBB2-negative patients were 44% in the pembrolizumab arm and 17% in the control arm. Among the 40 HR-positive/ERBB2-negative patients, the estimated pCR rates were 30% and 13%, respectively. In the 29 TNBC patients, the estimated pCR rates were 60% and 22%, respectively.

Extensive residual cancer burden was less often seen in the pembrolizumab-treated patients than in the comparison group. At a median follow-up of 2.8 years in the pembrolizumab arm and 3.5 years in the NAC arm, 3-year event-free survival was similar between the arms. However, the investigators cautioned against drawing conclusions from this exploratory analysis in a small number of patients. Testifying to the importance of the primary endpoint of pCR rate, patients who achieved pCR had excellent outcomes regardless of their assigned study arms.

Immune-related adverse events in the pembrolizumab-treated patients were generally grade 1 or 2 and were managed with dose interruption or corticosteroid therapy. Most commonly seen was thyroid dysfunction in 13% of patients, as in previously published reports. Adrenal insufficiency occurred more often than expected (8.7%), for unclear reasons, with five of the six reported cases occurring more than 30 days after the last dose of pembrolizumab.

The Bigger Picture: Putting I-SPY2 Results Into Context

It is well known that responses to pembrolizumab monotherapy in patients with advanced, refractory breast cancer are infrequent. In contrast, in previously untreated patients with PD-L1-positive TNBC, pembrolizumab monotherapy produced a response rate of 21% in . This response rate is similar to that observed with standard chemotherapy, but responses with pembrolizumab were more durable.

In the phase 3 , researchers are comparing pembrolizumab plus chemotherapy to placebo plus chemotherapy in patients with previously untreated, stage IV TNBC with high PD-L1 expression. Researchers saw a significant and clinically meaningful improvement in progression-free survival in the pembrolizumab arm, according to a recent announcement from Merck. These results lend credence to the I-SPY2 authors' hypothesis that immune-targeted agents would show their greatest benefit in early-stage breast cancer patients.

In fact, results from I-SPY2 have been confirmed by results from the phase 3 , which were recently published and presented at the San Antonio Breast Cancer Symposium. I-SPY2 predicted that pembrolizumab would be superior to standard NAC in TNBC patients in a phase 3 trial, and it was.

In KEYNOTE-522, the pCR rate was significantly higher in early-stage TNBC patients who received pembrolizumab plus NAC than in early-stage TNBC patients who received placebo plus NAC. The pCR rate was 64.8% in the pembrolizumab-NAC arm and 51.2% in the placebo-NAC arm (estimated treatment difference, 13.6 percentage points; 95% CI, 5.4-21.8; P裸艺 < .001).

These results are exciting. Results from I-SPY2 and KEYNOTE-522 whet the appetite for results of , an ongoing trial of pembrolizumab plus NAC in HR-positive/ERBB2-negative patients. Hopefully, the efficacy and toxicity results of KEYNOTE-756 will be as exciting as the I-SPY2 results predict they will be. Among patients with early-stage breast cancer whose tumor characteristics are adverse enough to require NAC, better regimens are needed to attain pCR, a validated surrogate for long-term freedom from recurrence.

Alan Lyss, MD, was a community-based medical oncologist and clinical researcher for more than 35 years before his recent retirement. His clinical and research interests were focused on breast and lung cancers as well as expanding clinical trial access to medically underserved populations.

This article first appeared on .

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