Replimune Stock Plummets 56% as FDA Rejects Key Melanoma Drug RP1

Replimune Group Inc. faces a severe market crisis as its shares collapsed by 56% in a single session, extending prior losses. The catalyst is a decisive and damaging regulatory blow: the U.S. Food and Drug Administration (FDA) has issued a complete response letter rejecting the company's lead candidate, RP1, for the treatment of melanoma. This is not a request for minor data; it is a full refusal that halts the drug's path to market and shatters near-term commercial expectations for the biotech firm.

The rejection of RP1, an oncolytic immunotherapy, represents a catastrophic failure at a critical juncture. The company had positioned this asset as its primary value driver in the competitive oncology space. The immediate 56% plunge in share price reflects a massive repricing of the company's entire pipeline and future revenue potential, erasing hundreds of millions in market capitalization almost instantly. Investor confidence has been fundamentally undermined, as the core thesis for investing in Replimune has now been invalidated by the primary U.S. regulator.

The fallout extends beyond the stock ticker. This event triggers intense scrutiny of Replimune's remaining clinical programs and its overall scientific platform. The company now faces immense pressure to conserve cash, reassess its development strategy, and potentially seek partnerships or restructuring to survive. For the broader biotech sector, especially other firms developing oncolytic viruses, the FDA's stance on RP1 may signal a more challenging regulatory environment, prompting investors to re-evaluate risk across the category.