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Pembrolizumab a 'game changer' in some triple-negative breast cancers

NEW YORK 23/09 - Adding pembrolizumab to chemotherapy as first-line treatment significantly prolongs overall survival in women with locally recurrent unresectable or metastatic triple-negative breast cancer (TNBC) with a PD-L1 combined positive score of at least 10, according to final results from the KEYNOTE-355 study.

The findings support pembrolizumab plus chemotherapy as a "new standard-of-care treatment regimen" in these patients, Dr. Hope Rugo of the University of California Helen Diller Family Comprehensive Cancer Center, in San Francisco, said in a presentation at the European Society for Medical Oncology (ESMO) 2021 Congress.

In the trial, 847 women were randomly allocated to add pembrolizumab or placebo to chemotherapy (nab-paclitaxel, paclitaxel or gemcitabine/carboplatin) for the first-line treatment of metastatic TNBC.

During a median follow-up of 44.1 months, overall survival (OS) was significantly improved in patients who received pembrolizumab, Dr. Rugo reported. The difference was almost seven months, from 16.1 months with placebo to 23.0 months with pembrolizumab, with a hazard ratio of 0.73, "or a relative improvement of 27%, and a P value of .0093," she noted.

There was no added benefit for pembrolizumab in tumors with a PD-L1 combined positive score of 1 or lower and no new safety signals emerged.

"These latest findings are really significant in a disease in which OS has remained poor and unchanged for years," Dr. Maria Vittoria Dieci of the University of Padua, in Italy, commented in an ESMO news release.

"Due to the mode of action of immunotherapy, the OS gain can often outperform the progress-free survival (PFS) gain and this is what we saw in KEYNOTE-355 - with advantages for pembrolizumab over chemotherapy of four months and seven months for PFS and OS, respectively," Dr. Dieci said.

In an email to Reuters Health, Dr. Amy Tiersten, professor of medicine, hematology and medical oncology at Icahn School of Medicine at Mount Sinai, in New York City, said, "Immunotherapy has been a game changer in the treatment of cancer overall but this is the first time that it has been shown that immunotherapy, when added to chemotherapy, has actually shown a significant improvement in overall survival in patients with triple-negative breast cancer who are PDL-1 positive (CPS >10)."

"The KEYNOTE-355 trial had previously shown an improvement in progression-free survival but with further followup/analysis, this survival benefit is very exciting," said Dr. Tiersten, who wasn't involved in the trial.

"Triple-negative breast cancer is a sub-type of breast cancer for which we previously did not have targeted therapy. These are aggressive cancers for which we don't have many great treatment options. Moreover, it is very rare for any combinations in metastatic breast cancer to show a survival benefit as compared to single agent therapy," Dr. Tiersten added.

The study was funded by Merck. Several authors have disclosed financial relationships with the company.

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