SELLAS Life Sciences Group has gained 45% in a week, yet short sellers have barely moved — and the borrow market is tightening again.
A week ago this note flagged the tension between a rallying biotech and an entrenched short base. That tension has not resolved. The stock has climbed from $5.22 to $7.59, driven by the Q1 earnings beat and mounting anticipation around the leukemia pipeline readout. Short interest now runs at nearly 40% of the free float — up from 30.6% cited in last week's note, a meaningful jump that confirms bears are not covering into the rally. The short score reads 84.8, down slightly from a peak above 86 earlier this month but still deep in extreme territory and ranking in the first percentile across the universe.
The borrow picture has tightened sharply. Availability has dropped to just 7% of short interest — roughly one share still available to lend for every fourteen already borrowed. Earlier in the week availability briefly touched 4%, close to the 52-week low of 0.06%. Cost to borrow has eased from above 16% in early April to around 13%, but that remains expensive, and the direction-of-travel on availability is the more pressing signal right now. Bears are paying a real cost to maintain exposure into a stock that just ripped nearly 50% in a month. Options positioning has shifted to match. The put/call ratio hit 0.12 on Tuesday — a 52-week high and more than 2.7 standard deviations above its 20-day average of 0.07. That is a dramatic reversal from the call-dominated positioning of recent weeks, suggesting hedging demand has spiked hard alongside the price move.
The earnings history adds useful context. The most recent event on May 12 produced a 24% next-day gain and a 45% five-day move — that is the rally now embedded in this week's price. The prior event in March delivered a flat-to-negative five-day reaction. The pattern is erratic, which is typical for a clinical-stage name where each readout carries binary risk. The next scheduled event is June 16, which puts the trial readout squarely in frame. Among correlated peers, QUCY is the outlier this week — up an extraordinary 680% over seven days before pulling back 24% on Tuesday — while WHWK rose a modest 4% and NVCT dropped 5%. The peer moves suggest the volatile small-cap biotech tape is bifurcating sharply, and SLS is on the winning end of that split for now.
Analyst coverage remains thin and dated. The most recent action came from Maxim Group in March, raising the target to $10 — a level now only modestly above the current $7.59. Most of the remaining coverage dates to 2023 or earlier and carries stale targets that predate the current price regime entirely. Institutional flows are more interesting: BlackRock added over 4.6 million shares as of April 30, and State Street added more than 6.2 million in the same period. Those are not trivial builds. Insider data is too old to carry weight here — the most recent trades date to December 2025 when the stock was trading near $1.50, and the context has changed entirely.
What to watch now is whether the short base begins to crack ahead of the June 16 event or digs in further. Availability at 7% leaves very little room for new short-sellers to enter — but it also means any forced covering could amplify a move in either direction.
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