Atossa Therapeutics, Inc. · NASDAQ:ATOS
Atossa Therapeutics — Investor Presentation (September 2026)
29 slides from Atossa Therapeutics's investor presentation, September 2026
Slide 1: Advancing (Z)-Endoxifen
Advancing (Z)-Endoxifen A potential best-in-class oral SERM/SERD for estrogen-driven diseases NASDAQ: ATOS Corporate & Investor Presentation www.atossatherapeutics.com September 2026 Seattle, Washington
Slide 2: Cautionary Note Regarding Forward Looking Statements
Cautionary Note Regarding Forward Looking Statements This presentation contains certain “forward-looking statements” within the meaning of applicable securities laws, including but not limited to, our expectations regarding the Company’s development and regulatory strategy and related milestones and
Slide 3: Investment Thesis: One Molecule, Multiple Value Streams
Investment Thesis: One Molecule, Multiple Value Streams $26.1M No debt ~800 3 $100 – $220M cash and equivalents at June 30, no debt outstanding at June 30, 2026 patients dosed with (Z)-endoxifen to FDA RPD for both MAS and DMD; disclosed PRV sale range, last 18–24 2026 date FDA ODD for DMD months* 1
Slide 4: (Z)-Endoxifen Is More Potent and Direct-Acting than Parent Drug Tamoxifen
(Z)-Endoxifen Is More Potent and Direct-Acting than Parent Drug Tamoxifen ~22 active metabolites generated by hepatic conversion, of parent drug tamoxifen, of which (Z)-endoxifen is the most active (Z)-endoxifen is30x to 100x more potent as an estrogen receptor- targeted therapy compared with parent
Slide 5: (Z)-Endoxifen Targets Distinct Disease Biology Through Multiple Pathways
(Z)-Endoxifen Targets Distinct Disease Biology Through Multiple Pathways Estrogen-Driven Diseases MAS and ER+ Breast Cancer • Antagonizes ERα signaling and promotes ERα degradation, suppressing estrogen-driven proliferation • Inhibits PKCβ1 and downstream AKT-associated proliferative signaling • Tar
Slide 6: (Z)-Endoxifen – One Molecule, Two Markets
(Z)-Endoxifen – One Molecule, Two Markets PRECLINICAL PHASE I PHASE II PHASE III Rare Diseases McCune-Albright Syndrome (MAS) IND clearance anticipated in 2H26, Ph 2 initiation in 2027 ER-targeting of precocious puberty in young girls Duchenne Muscular Dystrophy (DMD) IND clearance anticipated in 2H
Slide 7: McCune-Albright Syndrome
MCCUNE-ALBRIGHT SYNDROME (Z)-Endoxifen Targeting estrogen-driven pathology in McCune-Albright Syndrome (MAS)
Slide 8: MAS-Associated Precocious Puberty Drives Irreversible Loss of Adult Height Potential
MAS-Associated Precocious Puberty Drives Irreversible Loss of Adult Height Potential ~85 – 90% ~3 – 4.5 yrs 2 – 4x ~150.5 cm of girls with MAS develop peripheral precocious median age at first sign; onset is typically before rate at which bone age can outpace median adult height vs. ~160 cm mid-pare
Slide 9: Off-Label Agents Slow the Disease but None Deliver Complete Estrogen Receptor Blockade
Off-Label Agents Slow the Disease but None Deliver Complete Estrogen Receptor Blockade The unmet need: no FDA- or EMA-approved therapy exists for MAS-PPP, and no agent provides consistent, complete estrogen receptor blockade at the growth plate. Every option available is off-label use of a generic m
Slide 10: (Z)-Endoxifen Targets the Pathway Current Therapies Leave Incompletely Blocked
(Z)-Endoxifen Targets the Pathway Current Therapies Leave Incompletely Blocked by Two Mechanisms Bypasses need for liver metabolism • Administered as the active tamoxifen metabolite itself, the ~7 – 10% poor- metabolizer problem that limits tamoxifen does not apply • Higher ER affinity and greater a
Slide 11: Four Proof Points Underpin a Registrational Path in MAS-Associated Precocious Puberty
Four Proof Points Underpin a Registrational Path in MAS-Associated Precocious Puberty 1 Mechanistic Evidence 2 The Target Is Already Clinically Validated Transcriptomic strategy: definition of shared and • Tamoxifen (multicenter prospective): bleeding reduced ~65%; ΔBA/ΔCA improved 1.21 → 0.72 treat
Slide 12: Duchenne Muscular Dystrophy
DUCHENNE MUSCULAR DYSTROPHY (Z)-Endoxifen A mutation-agnostic approach acting downstream of dystrophin defects in Duchenne Muscular Dystrophy (DMD)
Slide 13: Without Dystrophin, Every Contraction Damages the Muscle
Without Dystrophin, Every Contraction Damages the Muscle A structural defect becomes a self-reinforcing cycle of injury, inflammation, and permanent tissue loss. The cascade and where it ends up → → → → Membrane instability Ca²⁺ influx & Chronic Fibrosis & fat Progressive during contraction fiber da
Slide 14: There is Significant Need for a Therapy That Works Downstream, for Every Genotype
There is Significant Need for a Therapy That Works Downstream, for Every Genotype Mutation-specific approaches reach only part of the population. The damage cascade is shared by all of it. What such a therapy must do And move the outcomes that matter 1 Work regardless of mutation Act downstream of t
Slide 15: (Z)-Endoxifen: One molecule, Six Downstream Pathways
(Z)-Endoxifen: One molecule, Six Downstream Pathways Published preclinical studies and early clinical reports in DMD models suggest benefit across membrane integrity, calcium handling, muscle preservation and cardiac function (Z)-Endoxifen may act downstream of the dystrophin mutation on six disease
Slide 16: (Z)-Endoxifen Safe and Efficacious in Preclinical Models
(Z)-Endoxifen Safe and Efficacious in Preclinical Models Preclinical Safety and Efficacy • Early-life treatment: In mdx5Cv mouse model of DMD, dystrophic pups, endoxifen lowered plasma creatine kinase (CK) levels and reduced centronucleated fibers, suggesting less initial myonecrosis and muscle infl
Slide 17: Four Proof Points Support a Development Path in Duchenne Muscular Dystrophy
Four Proof Points Support a Development Path in Duchenne Muscular Dystrophy 1 Broad, Mutation-Agnostic Therapeutic Rationale 2 Demonstrated Evidence Supporting Potential Cardiac Benefit • Targets downstream pathways implicated in DMD pathophysiology, including calcium • Tamoxifen preserved cardiac f
Slide 18: Breast Cancer Programs
(Z)-Endoxifen BREAST CANCER PROGRAMS Potential to be ideal combination drug candidate
Slide 19: Problem: High unmet need for endocrine therapy in breast cancer
Problem: ~40-50% ~50% ~60% High unmet need for endocrine therapy in breast Patients Discontinue First Line: Second Line: cancer Adjuvant Endocrine Tumors Do Not Respond Patients Do Not Benefit from Therapy Aromatase Inhibitors + CDK4/6 fulvestrant monotherapy Although, endocrine therapy remains the
Slide 20: (Z)-Endoxifen: Potential Best-in-Class SERM/SERD
(Z)-Endoxifen: Potential Best-in-Class SERM/SERD Superior ER ESR1 Mutant PKCβ1 Inhibition Antagonist Inhibition AKT1 PIK3CA mTOR 30x to 100x more potent vs other SERMs Binds to and inhibits protein kinase C beta Inhibits clinically relevant ESR1 mutants, one (PKCβ1, a known oncogenic protein) an acq
Slide 21: (Z)-Endoxifen – Improved Adherence, Potential Recurrence Rate Reduction
(Z)-Endoxifen – Improved Adherence, Potential Recurrence Rate Reduction Breast Density Reduction Safety Comparison (KARISMA Endoxifen) AE based discontinuations KARISMA: • Unmet need to reduce MBD. Reduced MBD correlates with reduced breast cancer risk 5.0% 6.3% • (Z)-endoxifen has demonstrated 1 mg
Slide 22: (Z)-Endoxifen Exhibits Superior Anti-tumor Pharmacology in Neoadjuvant Setting
(Z)-Endoxifen Exhibits Superior Anti-tumor Pharmacology in Neoadjuvant Setting Clinical (Z)-endoxifen demonstrates promising tumor response in neoadjuvant setting Superior anti-tumor activity Ki67 From Baseline % Decrease in Tumor Size at demonstrated in to Cycle 1, Day 28 Cycle 3 measured by MRI Im
Slide 23: (Z)-Endoxifen Represents an Ideal Combination Partner in Breast Cancer
(Z)-Endoxifen Represents an Ideal Combination Partner in Breast Cancer (Z)-Endoxifen with CDK4/6 (Z)-Endoxifen plus Ovarian inhibitors Function Suppression • CDK4/6 inhibitors are FDA-approved • GnRH receptor antagonist for management combination partners of pain associated with endometriosis; FDA f
Slide 24: Experienced Leadership & World-renowned Advisors
Experienced Leadership & World-renowned Advisors LEADERSHIP Steven Quay, Mark Daniel, Delly Behen, PHR, SHRM- Janet Rea, MD, PhD CPA CP MSPH Chairman, CEO and President Chief Financial Officer SVP, Business Operations SVP, Research & Development SCIENTIFIC ADVISORS Per Hall, Laura Esserman, Matthew
Slide 25: (Z)-Endoxifen: Closing Summary
(Z)-Endoxifen: Closing Summary • Oncology: Underwritten core • Rare Disease: Clinical-stage expansion, low-cost studies with accelerated timelines to pivotal data readouts • Platform • Oral SERM/SERD; ~800 patients exposed, no maximum tolerated dose reached • Given as the active metabolite, consiste
Slide 26: Thank you
Investors: ATOS@waterseid.com Thank you Media: Atossa@elev8newmedia.com
Slide 27: Appendix
Appendix
Slide 28: Appendix: Key Scientific References
Appendix: Key Scientific References Tamoxifen, Endoxifen & SERM Biology Mammographic Breast Density (MBD) & Prevention • Johnson MD et al. Pharmacological characterization of 4-hydroxy-N-desmethyl tamoxifen, a • Cuzick J et al. Tamoxifen-Induced Reduction in Mammographic Density and Breast Cancer Ri
Slide 29: Appendix: NCT References
Appendix: NCT References 1. NCT05607004: (Z)-Endoxifen for the Treatment of Premenopausal Women With ER+/HER2- Breast Cancer (EVANGELINE) 2. NCT05068388: Effect of Oral (Z)-Endoxifen in Premenopausal Women With Measurable Breast Density (Sweden) 3. NCT01042379: I-SPY TRIAL: Neoadjuvant and Personali
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