Immunomedics Inc.'s sacituzumab govitecan reduced tumor size in patients with a certain type breast cancer who had been previously treated.

The Morris Plains, N.J.-based biopharmaceutical company said the drug showed an overall response rate of 31% in 54 heavily pre-treated patients with a spreading breast cancer having the estrogen receptor-positive/human epidermal growth factor receptor 2-negative genes.

Overall response rate is the percentage of patients whose tumors shrank by a predefined amount and for a minimum amount of time.

Immunomedics said the drug was generally well tolerated with no treatment-related deaths. At six months about 48% of patients saw a clinical benefit after beginning treatment.

In September 2017, the company reported that the drug showed anti-cancer activity in metastatic urothelial cancer patients who did not respond to chemotherapies or treatments based on immune checkpoint inhibitors.

The company said it will present additional findings at the 2018 American Society of Clinical Oncology meeting on June 3.