Sophiris Bio has received a green light to begin dosing patients in a Phase 2b U.S. clinical trial of topsalysin (PRX302) for prostate cancer. The go-ahead was in the form of a Federal Drug Administration approval of a substance that Sophiris uses to dilute topsalysin, according to a press release. The therapy is for an enlarged prostate as well as cancer that has yet to spread from the prostate. The multi-center trial (NCT03081481) will evaluate the effectiveness and safety of topsalysin in 40 patients with localized prostate cancer. Effectiveness will be assessed with MRI scans and biopsies 24 weeks after treatment. Safety and tolerability will be assessed within 26 weeks of treatment. Last month the company reported that some patients with localized prostate cancer benefited from topsalysin. The results came from a small Phase 2a proof-of-concept study (NCT02499848). The trial’s primary goals were to evaluate the effectiveness and safety of a single injection of topsalysin directly to 18 patients' prostate tumors. Patients were followed at day 2, and then at two, six, 12, 24, and 26 weeks. At week 24, researchers collected a biopsy from the treated area. Researchers said the biopsies showed that two patients achieved a complete response to treatment — that is, all signs of their cancer were gone — at six months. Seven patients achieved a partial response — either a decrease in tumor size or severity of the disease. The other nine patients did not respond to treatment. In fact, the tumors of some became larger, and in some the disease progressed. Topsalysin was both safe and well-tolerated, researchers found. The safety results were consistent with what researchers saw in 365 prostate cancer patients who took topsalysin in Sophir