MacroGenics’ Breast Cancer Treatment Disappoints in Phase III

 

Trastuzumab stood its ground against MacroGenics’ MARGENZA treatment in a recent late-stage trial. On Tuesday, the biopharmaceutical company announced the final overall survival (OS) analysis of its SOPHIA Phase III study in adults with metastatic HER2-positive breast cancer.

According to the results, MARGENZA plus chemotherapy failed to show a statistically significant advantage when compared to trastuzumab plus chemotherapy in the intent-to-treat population.

In the study, median survival was 21.6 months for those who were treated with MARGENZA plus chemotherapy compared to 21.9 months for those that were treated with trastuzumab plus chemotherapy.

The disappointing results came as a surprise to some, as MARGENZA plus chemotherapy received U.S. Food and Drug Administration (FDA) approval last year to treat adults with metastatic HER2-positive breast cancer who have received two or more prior anti-HER2 regimens, with at least one being for metastatic disease.

Last year’s approval was based on progression-free survival (PFS) results from the SOPHIA study, where MARGENZA plus chemotherapy showed a 24% reduction in the risk of disease progression or death when compared to trastuzumab plus chemotherapy, and a 22% objective response rate versus 16% for the trastuzumab treatment.

Although the OS analysis as a whole was a letdown, there were some silver linings in the data.

“While the OS results in the SOPHIA ITT population are disappointing, the greater OS observed in the CD16A subgroup of patients with the lowest binding allelic variant of CD16 to the Fc region of IgG1 — namely, the F/F allele representing about 40% of all individuals (35.8% in this study) — is consistent with enhancements observed in MARGENZA’s engineered Fc region,” said Scott Koenig, M.D., Ph.D., president and CEO of MacroGenics.

Koenig went on to say that further studies will be needed to determine the impact of MARGENZA on HER2-positive breast cancer patients with different CD16A allelic variants.

“We continue to believe MARGENZA may be the right choice for certain patients,” Koenig said.

The SOPHIA study is a randomized, open-label Phase III trial that enrolled 536 patients. The patients were randomized 1:1 to receive MARGENZA given intravenously at 15 mg/kg every three weeks or trastuzumab given intravenously at 6 mg/kg (or 8 mg/kg for loading dose) every three weeks in combination with one of four chemotherapy agents given at the standard dose.

MARGENZA is also being tested in the Phase II/III MAHOGANY trial in combination with checkpoint blockade to treat patients with HER2-positive gastroesophageal cancer and in combination with tebotelimab in certain HER2+ tumors.