Five Prime Therapeutics’ ongoing Phase 1 clinical trial has advanced to its Phase 1b expansion portion, in which researchers have begun giving breast, ovarian, and endometrial cancer patients an optimal dose of the company's immune checkpoint inhibitor, FPA150. “We are very pleased with the progress of our FPA150 clinical program,” Helen Collins, senior vice president and chief medical officer at Five Prime, said in a press release. “We have now dosed the first patient in the Phase 1b dose expansion portion of the trial.” “FPA150 specifically targets B7-H4, which is in the same family of checkpoint inhibitors as PD-L1 and is over-expressed in breast and gynecological cancers that are not well served by immunotherapy,” Collins added. This antibody works in two ways. It blocks signals from B7-H4 that prevent immune cells from detecting and eliminating cancer cells, similar to commercially available checkpoint inhibitors, and directly kills B7-H4-positive cells. The Phase 1 trial (NCT03514121) was planned to include two parts. In Phase 1a, researchers included 10 patients with any solid tumor to explore the maximum tolerated dose and recommended dose of FPA150 for further testing. In Phase 1b, researchers will continue studying the selected dose only in breast, ovarian, or endometrial cancer patients with high levels of the B7-H4 protein in their tumor. During the second part of the trial, researchers will continue to evaluate the safety profile of this potential immunotherapy for these groups of patients. They will also collect early efficacy data, particularly overall response rate, duration of response, and the time patients live without disease worsening. Some patients in this portion will also undergo biopsies before and during treatment, so that researchers can examine FPA150's effects in the tumor and its microenvironment, including changes in infiltrated immune cells and inflammatory molecules, called cytokines. “We are hopeful that a targeted immunotherapy like FPA150 will provide clinical benefit to these patients who have limited treatment options,” Collins said. The study is still recruiting participants across eight clinical centers in the United States. For more information, go here or contact Sandeep Inamdar at FPA150email@example.com.