Dr Mileshkin on the Efficacy of Puxi-Sam in Gynecologic Cancers

“We saw responses regardless of histological subtype or the level of B7-H4 expression, although all the patients included did have B7-H4–positive tumors, which were selected based on immunohistochemistry testing.”

Mileshkin emphasized the clinical activity with Puxi-Sam that was observed in patients with B7-H4–positive tumors, who were selected based on immunohistochemistry testing demonstrating at least 25% target expression. Mileshkin detailed the outcomes in the ovarian cancer cohort, in which patients achieved an overall response rate (ORR) of 24.4% (95% CI, 12.9%-39.5%). She noted that these responses were durable, with a median duration of response (DOR) reaching 7.0 months (95% CI, 4.0-14.8) and a median progression-free survival (PFS) of 5.7 months (95% CI, 4.1-9.5). A key finding highlighted by Mileshkin was that clinical responses were observed regardless of the histological subtype or level of B7-H4 expression, provided the tumors met the initial positivity threshold for the study.

Furthermore, Mileshkin focused on the endometrial cancer cohort, which exhibited even more pronounced clinical activity at the 2.4-mg/kg dose of Puxi-Sam selected for further testing. In this group, the ORR was 47.1% (95% CI, 32.9%-61.5%). The median DOR was 7.1 months (95% CI, 4.5-13.3), and the median PFS was 7.2 months (95% CI, 5.6-9.2). She explained that these benefits extended across various histological subtypes, including hard-to-treat cases, such as serous disease and carcinosarcoma. The activity was particularly impressive in a subset of patients who had previously received both platinum-based chemotherapy and immunotherapy, where the ORR was well preserved at 60.6% with a median PFS of 7.1 months. The data in the endometrial cancer cohort reinforce the rationale for the ongoing phase 3 BLUESTAR-Endometrial01 trial (NCT07044336) investigating Puxi-Sam vs chemotherapy in patients with B7-H4–selected endometrial cancer.