Dr. McGregor on double ADC trial in metastatic urothelial carcinoma

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“The recommended phase 2 dose was dose level 2, so 8 mg/kg of SG with EV 1.25mg/kg,” says Bradley McGregor, MD.

In this video, Bradley McGregor, MD, shares data from the phase 1 double antibody drug conjugate (DAD) trial (NCT04724018) of sacituzumab govitecan plus enfortumab vedotin in metastatic urothelial carcinoma, which he presented at the 2023 European Society for Medical Oncology Annual Congress in Madrid, Spain. McGregor is the director of clinical research at the Lank Center for Genitourinary Oncology at Dana-Farber Cancer Institute in Boston, Massachusetts.

Video Transcript:

What we found overall is when we look at this through the BOIN design, we enrolled 23 patients. The median age of the patient is 70; patients were up to age 88. [The] majority of patients had at least 2 lines of therapy. Only 1 patient progress on IO alone, a quarter of them had liver and/or bone mass. These were not just lymph node only to these patients. 23 patients are enrolled, 9 patient enrolled at dose level 1, 8 enrolled at dose level 2, and 6 were enrolled at dose level 3. Of the 6 enrolled at dose level 3, 1 patient didn't receive day 8 of therapy during cycle 1 and was inevaluable for DLT assessment.

What we saw overall is that the maximum tolerated dose, was dose level 3. So, full dose EV and SG was the maximum tolerated dose. Of evaluable patients, there was 3 DLTs, 1 due to neutropenic fever, 1 due to delay in therapy, and 1 due to mucositis. When we looked at the other dose levels, dose level 1 there was 2 DLTs both neutropenic fever. In dose level 2, there was actually 1 DLT for a delay in treatment.

All this together, we have to look a little bit further, and I will note that when protocol first started, we did not allow prophylactic GCSF was cycle 1. But after we saw 2 out of the first 6 patients initiating fever and no other signs of toxicity, we allowed it for investigator discretion, given that often investigators will give this new prophylactic GCSF with SG. In such way most patients on a trial did get prophylactic GCSF with cycle 1. The caveat is the maximum tolerated dose is the full dose with GCSF support.

But we looked a little bit further, the recommended phase 2 dose isn't the maximum tolerated dose. When we look at the patients on trial, the median number of cycles at the MTD was 1. When we look at DL2, only 1 DLT and a majority of patients will undergo at least 3 to 4 cycles. Given that EV is approved at 1.25 mg/kg dose based on phase 3 data, the recommended phase 2 dose was dose level 2, so 8 mg/kg of SG with EV 1.25mg/kg. Both recommend dose 1 on day 8 of a 21-day cycle with prophylactic GCSF per investigator discretion.

This transcription has been edited for clarity.

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