Protagonist Therapeutics says the Food and Drug Administration plans to revoke its breakthrough designation for a blood cancer drug, and PTGX stock collapsed Thursday.
The company disclosed the news in a Securities and Exchange Commission filing and a presentation to investors on Wednesday. The FDA cited "observed malignancies" tied to Protagonist's rusfertide in patients with polycythemia vera, a rare disorder in which the blood thickens.
Protagonist says the FDA decision doesn't impact the fast-track designation for rusfertide. The FDA expedites its review on experimental drugs, with fast-track or breakthrough medications among them. Breakthrough drugs could show a substantial improvement over available therapies. Fast-track drugs treat serious conditions and unmet needs.
The company said it requested a meeting with the FDA and sent a briefing document arguing why it believes rusfertide still warrants a breakthrough designation. But on today's stock market, PTGX stock plummeted 21.8% to close at 19.95.
PTGX Stock Swings On Rusfertide Drama
Rusfertide has had an uphill battle in recent months. In September, the FDA placed the program on hold. The agency cited a study in which mice developed benign and malignant skin tumors after receiving rusfertide.
Less than a month later, the FDA allowed Protagonist to resume human testing. Protagonist said it provided patient safety data, and added new safety and stopping rules in the study protocols.
Amid the rusfertide drama, PTGX stock has yo-yoed. Shares tumbled 62% the day the FDA placed rusfertide testing on hold. Then, the biotech stock surged 94% when the FDA removed the hold.
Protagonist says rusfertide is already in Phase 3 testing. So far, five out of 89 polycythemia vera patients who received rusfertide have developed skin cancer. All had prior episodes of skin cancer. Some were advanced in age, had fair skin and a lot of sun exposure. Three of the patients also took medicines known to have cancer-causing side effects, Protagonist said in its presentation.
"No changes to the development plan or timeline are anticipated at this stage," the company said in its SEC filing.
PTGX stock tumbled to its lowest point since October. That followed a strong pop on Wednesday that led shares to butt up against their 50-day moving average, according to MarketSmith.com.
Follow Allison Gatlin on Twitter at @IBD_AGatlin.
