NEW YORK – Immunomedics said on Wednesday that its antibody drug conjugate sacituzumab govitecan-hziy (Trodelvy) was approved by the US Food and Drug Administration for previously treated metastatic triple-negative breast cancer.
The accelerated approval was based on the objective response rate and duration of response in a single-arm, Phase II study. The confirmatory Phase III ASCENT study was recently halted by an independent Data Safety Monitoring Committee (DSMC) due to compelling efficacy. The company said in a statement that proof of benefit from the Phase III trial may support continued approval for the drug, and it expects to announce topline results by mid-2020.
There is currently no approved standard therapy for patients with previously treated metastatic TNBC, an aggressive type of breast cancer that accounts for approximately 20 percent of all breast cancers, resulting in 13,000 cases in the US a year. In order to receive sacituzumab govitecan-hziy patients must be tested to establish that their cancer cells have the hallmarks of TNBC, including lack of HER2 protein, as well as no estrogen and progesterone receptors.
In the Phase II study that led to the drug's accelerated approval, investigators observed an overall response rate of 33.3 percent, and a median duration of response of 7.7 months. Among the patients who responded to treatment, 55.6 percent maintained their response for six or more months, and 16.7 percent maintained their response for more than a year. The responses were evaluated from 108 TNBC patients who, on average, had previously received three therapies for their metastatic disease.
Richard Pazdur, director of the FDA's Oncology Center of Excellence, said in a statement that Immunomedics' drug represented a new targeted treatment option for patients living with aggressive disease, for whom the main treatment option until now has been chemotherapy.
Sacituzumab govitecan-hziy is Immunomedics' lead antibody-drug conjugate directed to Trop-2, a cell-surface protein expressed in many solid cancers that supports cancer growth and spread, and linked to a topoisomerase inhibitor SN-38, which kills cancer cells.
Trop-2 is expressed on approximately 90 percent of TNBC cells.
"This approval highlights the potential of our unique ADC platform and strengthens the premise that the Trop-2 antigen found in many solid cancers is an important target for drug delivery," Immunomedics CMO Loretta Itri said in a statement. "We are committed to broadening the potential use of Trodelvy in other Trop-2-expressing cancers, especially those with unmet need."
A company spokesperson said in an email that Immunomedics did not have any plans to develop or collaborate on a companion diagnostic to detect Trop-2 expression in cancers.
Trodelvy has a black box warning for severe neutropenia, or abnormally low levels of white blood cells, and diarrhea, which were among the most common adverse reactions that occurred in the trial for more than 25 percent of patients. Other common adverse reactions include nausea, fatigue, anemia, vomiting, alopecia, constipation, decreased appetite, rash, and abdominal pain. In total, 2 percent of patients discontinued treatment due to adverse events, but according to Immunomedics, no treatment-related deaths occurred during the trial and no patients suffered severe cases of neuropathy or interstitial lung disease.
During a call with investors on Wednesday, the company said the drug would be priced at $2,012.50 for a 180 mg vial, and that one course of treatment would consist of four vials.
In early Thursday morning trading on the Nasdaq, Immunomedics' stock was up nearly 25 percent at $27.45.