Let's talk about a stock that's having a very good year. SELLAS Life Sciences Group Inc. (SLS) is up over 200% in the last six months. That's the kind of move that gets people's attention. It's up about 45% year-to-date, but the real story is the longer-term rocket ride.
Now, when a stock moves like this, you have to ask: why? Part of the answer is in the company's actual business—it's a cancer drug developer, and it's had some promising news lately. But another part of the answer might be a bit more mechanical. According to market data, the short interest in SELLAS is sitting pretty high, at 27.21%. That's a lot of people betting the stock will go down. When a stock with high short interest starts going up instead, it can create what's called a short squeeze, where those short sellers have to buy shares to cover their positions, which pushes the price up even more. It's a feedback loop that can be very powerful, for better or worse.
The stock's recent gains over the last three months have been fueled by two specific updates from the company's clinical trials.
Promising Data for a Leukemia Treatment
In December 2025, the company presented data at a major medical conference from a Phase 2 study. They're testing a drug called SLS009 in combination with two other drugs for patients with a specific, hard-to-treat form of acute myeloid leukemia (AML) that has come back or hasn't responded to treatment.
The results were encouraging. Among 35 patients they could evaluate, the overall response rate was 46%. That includes 29% of patients achieving what's called a complete remission or a complete remission with incomplete blood count recovery (CR/CRi). For context, the median overall survival for these patients was "exceedingly higher" than the expected 2.6 months for this patient population. In the group of patients who had received the least prior treatment, the median overall survival reached 8.9 months. In the world of oncology drug development, data like this gets investors excited.
An Update on a Pivotal Trial
Also in December, the company provided an update on its bigger, Phase 3 trial called REGAL. This trial is evaluating a different drug, Galinpepimut-S (GPS), as a maintenance therapy for AML patients who have achieved a second complete remission.
An independent committee had already recommended in August that the trial continue as planned. The key moment for this kind of trial is when a pre-specified number of "events" (in this case, patient deaths) occurs, which triggers the final analysis to see if the drug worked. The company expected that the 80th event would happen before the end of 2025. As of December 26, 2025, the company's research partner reported the pooled number of events was 72. So, they're getting close to that analysis point, which is a significant milestone.
