Sellas Life Sciences (NASDAQ: SLS) stock has surged roughly 100% year-to-date, closing around $2.14 on Oct. 17, 2025 ts2.tech ts2.tech (versus a 52-week low of $0.77). In after-hours trading on Oct. 17 it spiked another +38%, briefly touching a new 52-week high ts2.tech. Big investors are piling in: BlackRock disclosed a 5.4% stake (~5.7M shares) in SLS on Oct. 18 ts2.tech, and other funds like Vanguard and Marshall Wace added millions of shares in Q2 Quiverquant. On the drug-development front, Sellas’s lead AML immunotherapy (galinpepimut‑S, “GPS”) is in a Phase 3 AML trial (REGAL), which recently passed an interim safety review Sellaslifesciences; SLS’s CDK9 inhibitor (SLS009, tambiciclib) reported 44% response in a Phase 2 relapsed AML trial Sellaslifesciences and just showed statistically significant survival gains in a rare T-cell leukemia model ts2.tech Sellaslifesciences. The company will hold a virtual R&D Day on Oct. 29, 2025 to update investors on these AML programs ts2.tech, and final REGAL results are expected by late 2025 – potential near-term catalysts. Analysts are optimistic: Maxim Group reiterated a “Buy” and $7.00 12-month price target ts2.tech, and the consensus target (~$6–$7) implies ~220% upside ts2.tech Investing. Sellas ended Q2 2025 with ~$25M cash on hand ts2.tech and raised another $23.6M through warrant exercises in Sept. 2025 ts2.tech to fund its trials. Overall, investor sentiment is upbeat (social-media chatter highlights the new data and funding round) – though one independent rater still warns of biotech risk (Weiss gave SLS a “Sell (D-)” grade) ts2.tech Quiverquant.
Stock Performance and BlackRock’s Big Bet
In mid-October, Sellas’s stock extended a dramatic rally. Shares closed around $2.14 on Oct. 17, roughly double where they began 2025 ts2.tech. That day saw heavy buying: volume was 3× normal, and call-option volume spiked (~761% above average) ts2.tech ts2.tech. After the regular session, SLS jumped another ~38% to ~$2.94 on Oct. 17 after-hours ts2.tech ts2.tech. Tech indicators are bullish: the stock is well above its 20- and 50-day moving averages (TipRanks flags “Buy”) ts2.tech, and short interest is high (~18% of float) ts2.tech (short-sellers risk being squeezed if further catalysts emerge).
Investor interest spiked when BlackRock disclosed a new 5.4% ownership in Sellas on Oct. 18 ts2.tech. In its SEC filing, BlackRock reported ~5.7 million SLS shares, a significant position for a ~$230M market-cap biopharma. As analyst Marcin Frąckiewicz notes, this “effectively gives BlackRock a significant voting bloc” and “suggests growing institutional confidence” in Sellas ts2.tech. Other hedge funds also piled in: in Q2 BlackRock had added ~4.05M shares (a +752% increase), Vanguard added ~3.82M shares, and even high-profile quant funds like Marshall Wace, Geode, Millennium, and Morgan Stanley took notable stakes Quiverquant. At the same time, insiders have bought into the stock – for example, board members Katherine Kalin and Jane Wasman each recently bought 20,000 shares Quiverquant – suggesting company insiders are confident in the outlook.
Pipeline Progress and Clinical Data
The rally has strong scientific underpinnings. Sellas’s lead product, galinpepimut‑S (GPS), is a WT1-targeted cancer vaccine in a pivotal Phase 3 AML trial (REGAL). In August 2025 an independent Data Monitoring Committee reviewed ~60 events in REGAL and unanimously recommended the trial continue without changes Sellaslifesciences. No safety concerns were identified, and the committee confirmed the risk/benefit profile supports the study Sellaslifesciences. Under the current protocol, the final overall survival analysis is triggered at 80 events, expected by year-end 2025. Management expects that, if positive, the GPS data could lead to a FDA filing in 2026.
Sellas’s second therapy, SLS009 (tambiciclib), is an oral CDK9 inhibitor. In Q2 Sellas announced that the Phase 2 trial in relapsed/refractory AML met all primary endpoints, delivering a 44% overall response rate (ORR) in high-risk AML patients Sellaslifesciences. According to CEO Dr. Angelos Stergiou, this response rate “at the optimal dose level… nearly tripled the median overall survival compared to a historical benchmark” Sellaslifesciences, and based on the strength of these data the FDA agreed the drug can move into first-line AML studies. (Sellas plans an 80-patient trial in newly diagnosed or early-refractory AML, with enrollment in early 2026 Sellaslifesciences Sellaslifesciences.)
At the recent ESMO 2025 conference (Oct 17–21), Sellas presented new preclinical data on SLS009 in an aggressive T-cell leukemia (T-PLL). In a patient-derived mouse model, SLS009 – both alone and combined with the BCL2 inhibitor venetoclax – significantly extended survival compared to venetoclax alone ts2.tech. Treated mice lived ~7.4–7.9 weeks on SLS009 versus only ~4.4 weeks on venetoclax (p<0.05) ts2.tech. There were no new safety issues, and “blood tumor cells were markedly reduced” in the SLS009 arms ts2.tech. Sellas’s Chief Development Officer Dragan Cicic hailed these findings: “These results are highly encouraging and provide important preclinical evidence…” that CDK9 inhibition may play a critical role in treating T-PLL Sellaslifesciences. MD Anderson’s Dr. Francisco Vega (lead author) added that the T-PLL mouse model “closely mirrors” the human disease, enabling more rapid clinical translation of promising therapies like SLS009 Sellaslifesciences.
Upcoming Catalysts and R&D Day
Investors are eyeing near-term catalysts. Sellas will host a virtual R&D Day on Oct. 29, 2025 to review its AML pipeline ts2.tech. The event will feature key opinion leaders and company scientists discussing GPS and SLS009 data. Later this year, Sellas expects the final readout of REGAL (80-event analysis) for GPS in AML. A strong result there could pave the way for a regulatory filing in 2026. Conversely, any miss could trim expectations. CEO Stergiou has emphasized the company’s momentum: “With the final pivotal Phase 3 REGAL data of GPS in AML expected by year-end, positive Phase 2 data of SLS009 in r/r AML, and our upcoming ESMO presentation, we enter the second half of 2025 with tremendous momentum…” Sellaslifesciences.
Analyst Ratings and Forecasts
Wall Street analysts are largely bullish on Sellas. Most data aggregators show three analysts covering SLS, all with “Buy” ratings. Maxim Group’s Jason McCarthy maintained a Buy rating on July 16, 2025 and raised his 12-month target to $7.00 (from $4.00) ts2.tech Investing. Investing.com reports the average analyst target is about $6.83 (range $6.00–$7.50) Investing, implying roughly +219% upside. TechStock² notes the $6–$7 consensus range is ~220–240% above current levels ts2.tech. One contrarian view: Weiss Ratings recently assigned Sellas a low “Sell (D-)” grade ts2.tech, reflecting the inherent risks of small-cap biotech.
On technical grounds, some trading services flag Sellas as being in a strong uptrend. TipRanks notes SLS is trading well above its key moving averages ts2.tech. Coincodex’s short-term forecast (machine learning model) called for a high of ~$2.18 on Oct. 19, 2025, in line with recent trading. Of course, biotech stocks can be volatile: roughly 18% of SLS’s float is sold short ts2.tech, so any surprise (positive or negative) could drive sharp moves.
Financial Position and Partnerships
Sellas reported Q2 2025 financials on Aug 12, 2025 Sellaslifesciences. The company ended the quarter with $25.3 million in cash Sellaslifesciences, down from $29.3M at year-end but bolstered by a $4.0M inflow in July from warrant exercises Sellaslifesciences. Total net loss was $6.6M (or $0.07/share) for Q2 2025 Sellaslifesciences, an improvement from $7.5M a year earlier. R&D spending was relatively modest ($3.9M in Q2) Sellaslifesciences as enrollment in the REGAL trial concluded earlier in 2024. Sellas has since strengthened its balance sheet: on Sept. 11, 2025 it completed a financing that raised $23.6M (through warrant exercises) ts2.tech. That cash should fund operations through the upcoming trial readouts and the planned first-line SLS009 study.
On the corporate front, Sellas has expanded its scientific advisory board in recent months, adding experts like Drs. Philip Amrein, Alex Kentsis, and Linghua Wang Sellaslifesciences. Sellas also has collaborations for GPS: the vaccine was exclusively licensed from Memorial Sloan Kettering Cancer Center Sellaslifesciences, and is being studied in combination with Merck’s Keytruda (pembrolizumab) in a multi-cancer trial Sellaslifesciences. (Additionally, investigator trials have tested GPS plus Opdivo® (nivolumab) Sellaslifesciences.) There were no new partnership announcements in October 2025, but the ongoing collaborations underscore Sellas’s external validation.
Investor Sentiment and Outlook
Investor sentiment has turned decisively positive. Online forums and social media (e.g. StockTwits, Twitter/X) are abuzz with Sellas news. A QuiverQuant summary notes recent discussions focused on the upcoming R&D Day and trial updates, highlighting the stock’s 40% after-hours jump on new AML data Quiverquant and the fresh $23.6M funding. Some posts even speculate about potential buyouts or partnerships, given the strategic advisory involvement, though no deals have been announced Quiverquant. Overall, the market seems to be pricing in the upcoming catalysts.
What’s Next: The near-term calendar is heavy with milestones. Along with the Oct. 29 R&D Day, Sellas will likely report Q3 2025 results in late November, potentially with new updates on trials. Most importantly, the REGAL Phase 3 results could come before year-end. If those results (on overall survival) meet expectations, Sellas could file for FDA approval in 2026 – a “make-or-break” moment noted by analysts ts2.tech. Conversely, any disappointments could prompt profit-taking. For now, however, the combination of big-data stir (ESMO results), bullish analyst targets, and institutional backing (BlackRock, etc.) has the stock on a tear. All positions mentioned are speculative; biotech investments carry high risk.
Sources: Sellas official press releases and investor materials Sellaslifesciences Sellaslifesciences; TechStock² (ts2.tech) articles ts2.tech ts2.tech; Investing.com consensus data Investing; QuiverQuant discussion summary Quiverquant; financial news outlets (Finbold, Investing.com) ts2.tech ts2.tech. All data current as of October 20, 2025.
