Novel Breast Cancer Drug Meets Main Goal of Eliciting Treatment Responses

Treatment with praluzatamab ravtansine improved outcomes in some patients with breast cancer, though one expert noted further study of the drug is needed.

A novel drug, praluzatamab ravtansine, shrunk tumors in patients with HER-positive, HER2-non—amplified breast cancer, according to CytomX Therapeutics, the manufacturer of the drug.

“These results from our phase 2 evaluation of praluzatamab ravtansine support single-agent activity of this novel drug candidate in hormone receptor-positive breast cancer where significant unmet need remains,” said Sean McCarthy, CEO and chairman at CytomX Therapeutics, in a press release.

The study’s main goal, which was met, for a certain group of patients was a confirmed objective response rate (decreasing of cancer) by 10%. As of May 13, 2022, when trial data was most recently collected, the objective response rate was 15%. Further, at the 24-week mark, 40% of patients were experiencing clinical benefit, which means that their cancer responded to treatment and had stable disease.

On average, patients lived for 2.6 months without their disease progressing or getting worse.

Trial participants were divided into three groups:

  • Arm A, where patients with inoperable, locally advanced or metastatic HR-positive, HER2-non—amplified breast cancer were given praluzatamab ravtansine alone. Patients in this group could have received zero to two prior chemotherapies.
  • Arm B, where patients with locally advanced or metastatic triple-negative breast cancer (TNBC) received single-agent praluzatamab ravtansine. These patients could have had one to three prior chemotherapy treatments, and had disease that expressed CD166, a gene that could play a role in cancer.
  • Arm C, which included the same patient characteristics of Arm B. These patients were given praluzatamab ravtansine in combination with pacmilimab.

Of note, Arm B did not reach the objective response goal, and continued patient enrollment on to Arms B and C will be discontinued.

Regarding side effects, there were no new toxicities seen in this trial that were not previously seen in the phase 1 study of praluzatamab ravtansine. Overall, 30% of patients stopped therapy because of a side effect, with common severe side effects being ocular or neuropathic effects.

No patients who were administered the drug at 6 mg/kg (Arm C)had to stop treatment as a result of side effects, and this group also had a lower instance of ocular (related to the eyes or vision) or neuropathic events.

McCarthy explained, “We do not believe the median progression-free survival at 7 mg/kg supports further evaluation at this dose. While we are encouraged by the emerging safety profile of 6 mg/kg, we do not plan to further advance this program alone given current financial market conditions and will be seeking a partnership.”

The study will move forward with only Arm A, and the dose will be changed to 6 mg/kg.

The study’s lead investigator, Dr. Kathy D. Miller, associate director of clinical research at Indiana University Simon Comprehensive Cancer Center in Indianapolis, noted, “In this phase 2 study, praluzatamab ravtansine showed single-agent activity in an unselected population of patients with advanced HR+/HER2-non-amplified breast cancer; additional clinical studies at 6 mg/kg are warranted.”

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