SLS009 Shows Encouraging Phase 2 Data in High-Risk AML, but REGAL Remains Key

What happened

SELLAS announced that Phase 2 data for SLS009 in combination with azacitidine and venetoclax in relapsed/refractory AML will be presented at ASH 2026, showing 54% ORR and mOS 5.8 months in monocytic AML and 57% ORR with mOS 8.8 months in TP53-mutated AML, against historical ~2.5 months. This adds incremental validation to the second asset, but as of the last filing, the company's value remains dominated by the blinded Phase 3 REGAL trial, which was at 78 of 80 events as of May 11, 2026. The news does not address REGAL timing or potential dilution, and the stock traded at $11.10 with a market cap over $2 billion against no product revenue. While the SLS009 data are positive, they come from a small Phase 2 study in a difficult population, and the overall thesis still hinges on REGAL. The announcement may support the SLS009 pillar but does not resolve the primary binary risk.

Implication

Investors should treat this as incremental, not transformative, because SLS009 remains early-stage and the company's valuation already embeds significant success. The encouraging response rates could attract partnership interest or support further development, but the data are from a limited Phase 2 cohort and need confirmation in larger, randomized settings. Meanwhile, the primary value driver, REGAL, remains blinded and event timing has already slipped from prior guidance. The company has $138.3 million in cash, but dilution risk persists if data are delayed. Given the current premium valuation, this news alone is unlikely to justify chasing the stock; a more prudent approach is to wait for REGAL clarity or a substantial pullback.

Thesis delta

Thesis shift is modest: the new SLS009 data strengthen the second asset's clinical profile, supporting its potential as a future value driver. However, the core thesis remains unchanged as REGAL continues to dominate near-term valuation and risk. The update does not reduce the timing or efficacy uncertainty around the pivotal Phase 3 trial, so the overall stance of caution remains intact.