Uterine serous carcinoma (USC) is a distinct histologic subtype of endometrial cancer, with molecular characteristics suggesting frequent cell-cycle dysregulation paired with a high level of oncogene-driven replication stress. Adavosertib is a potent and selective oral inhibitor of the WEE1 kinase, a key regulator of the G2/M and S phase cell-cycle checkpoints. Because cells with impaired cell-cycle regulation and high replication stress may be vulnerable to WEE1 inhibition, we conducted this study to assess the activity of adavosertib monotherapy in women with recurrent USC.

This was a single-arm two-stage phase II study with coprimary end points of objective response rate (ORR) and rate of progression-free survival at 6 months (PFS6). Women with recurrent USC were treated with adavosertib monotherapy at a starting dose of 300 mg orally once daily days 1 through 5 and 8 through 12 of a 21-day cycle until disease progression.

In 34 evaluable patients, 10 total responses (one confirmed complete response, eight confirmed partial responses, and one unconfirmed partial response) were observed with adavosertib monotherapy, for an ORR of 29.4% (95% CI, 15.1 to 47.5). Sixteen patients were progression-free at 6 months, for a PFS6 rate of 47.1% (95% CI, 29.8 to 64.9). Median PFS was 6.1 months, and median duration of response was 9.0 months. Frequent treatment-related adverse events (AEs) included diarrhea (76.5%), fatigue (64.7%), nausea (61.8%), and hematologic AEs. No clear correlation of clinical activity with specific molecular alterations was observed in an exploratory biomarker analysis.

Adavosertib monotherapy demonstrated encouraging and durable evidence of activity in women with USC, and further investigation of this agent in this cancer and biomarkers of activity are indicated.