Rare Photodynamic Therapy Drug Faces Setback in First FDA Review, Additional Phase 3 Data Required

Disc Medicine, Inc. (NASDAQ: IRON) announced on February 13 that it received a complete response letter (CRL) from the U.S. Food and Drug Administration (FDA) regarding its new drug application (NDA) for bitopertin, a candidate therapy for erythropoietic protoporphyria (EPP), a rare disease. While the FDA acknowledged the reduction of protoporphyrin IX levels in the Phase 2 AURORA and BEACON trials, it determined that the connection between this biomarker change and improvements in sunlight-induced clinical symptoms was not sufficiently demonstrated. The agency has requested additional clinical evidence based on the ongoing Phase 3 APOLLO trial.

The company plans to complete patient enrollment in the APOLLO study by March 2026, release key data in the fourth quarter of 2026, and then resubmit its NDA—including the safety and efficacy results—to the FDA, targeting a renewed review decision by mid-2027. Disc Medicine will continue supplying bitopertin to current trial participants. As of the end of December 2025, the company reported approximately $790 million in cash and cash equivalents (about KRW 1.07 trillion), providing a financial runway through 2029 to cover the APOLLO readout and key pipeline milestones.

Following the CRL announcement, Disc Medicine’s shares plunged about 24%, dipping to around $49, reflecting the near-term impact. Nonetheless, into early this month, Wall Street analyst consensus has maintained a “Buy” bias, with a one-year average price target near $119. In January, Morgan Stanley also reiterated its Overweight rating and $120 price target on the stock amid the FDA review of bitopertin, underscoring continued institutional interest.

Disc Medicine is a U.S.-based biotech focused on developing therapies for rare blood disorders by targeting heme biosynthesis and iron homeostasis. Its pipeline includes treatments for severe conditions such as erythropoietic protoporphyria. While the rare hematology market has a substantial unmet need, it also demands rigorous proof of causality between surrogate biomarker changes and clinical symptom improvement, making clinical trial design and regulatory approval particularly challenging in this field.