As Seagen prepares for its takeover by Pfizer, the company’s Astellas-partnered cancer drug Padcev has chalked up a key trial win—in combination with Merck's Keytruda—in previously untreated metastatic bladder cancer.

In the study, Seagen and Astellas’ antibody-drug conjugate Padcev and Merck’s PD-1 superstar Keytruda scored on both overall survival and progression-free survival compared with chemotherapy. An independent data monitoring committee found that the combo’s life extension benefit surpassed the pre-specified efficacy boundary at an interim analysis, the companies said in a Friday release.

The results could open the combo up to patients who are eligible for platinum-based chemotherapies cisplatin or carboplatin, regardless of their PD-L1 status.

“This study has the potential to be practice changing and offer a new standard of care for first-line metastatic bladder cancer,” Seagen’s R&D head Roger Dansey, M.D., said in the release. “We look forward to presenting the results at an upcoming medical conference and discussing with regulators in order to get this medicine to patients as soon as possible.”

The combo in April won an FDA accelerated approval to treat first-line platinum-ineligible patients. Inclusion of the cisplatin-eligible population could nearly double the addressable market for Padcev to over $5 billion worldwide, William Blair analysts wrote in a Friday note to clients.

Furthermore, the analysts expect “rapid adoption” by physicians upon potential approval.

The results present an opportunity for Pfizer, too, as the Federal Trade Commission continues its review of the company's $43 billion buyout of Seagen. The pair expects to close the transaction by late 2023 or early 2024, Seagen said in a July filing.

Padcev scored its full approval in 2021 after an initial conditional approval for the same population as a third-line therapy in patients who already received platinum-based chemotherapy and a PD-1/PD-L1 checkpoint inhibitor.

At the same time, it also moved into second-line treatment for adults who are ineligible for cisplatin-based chemotherapy.