Faeth Therapeutics, Inc. (Nasdaq: FTH), the Austin, Texas-based clinical-stage oncology company, announced on October 19, 2026, that it will present new preclinical research evaluating PIKTOR, its investigational oral combination of serabelisib and sapanisertib, in hormone receptor-positive, HER2-negative breast cancer models. The findings are scheduled for presentation on October 23 at the European Society for Medical Oncology Congress in Madrid, Spain. The research examines whether simultaneously inhibiting PI3K-alpha, mTORC1 and mTORC2 can produce stronger suppression of cancer-associated signaling than approaches targeting fewer components of the same pathway. The poster will include laboratory experiments, mouse xenograft studies and direct preclinical comparisons with gedatolisib, another investigational multi-node pathway inhibitor.
Faeth is also evaluating PIKTOR alongside established and emerging breast cancer treatments, including fulvestrant, oral selective estrogen receptor degraders and CDK inhibitors. The company says its cellular experiments demonstrated suppression of key signaling components, including AKT, at levels comparable to or exceeding those observed with selected single-node inhibitors under the experimental conditions. However, the October announcement does not disclose complete numerical tumor regression results or the outcomes of the direct comparison with gedatolisib. Those data are scheduled for release with the ESMO presentation and must not be described as established clinical superiority.
The preclinical work is intended to support the ongoing FTH-PIK-101 Phase 1b/2 clinical trial in advanced hormone receptor-positive, HER2-negative breast cancer. The first participant received treatment in April 2026, and initial human safety and efficacy findings are expected during 2027. Faeth is separately developing PIKTOR in advanced endometrial cancer, with Phase 2 topline results anticipated before the end of 2026.
The research addresses a persistent challenge in targeted oncology: cancer cells can reactivate growth pathways after treatment blocks one signaling component. Faeth believes that inhibiting several related nodes simultaneously could reduce opportunities for compensatory signaling and acquired resistance. Whether that strategy improves clinical outcomes without creating unacceptable toxicity remains the central question for its development programme.
Why is the PI3K-AKT-mTOR pathway important in breast cancer?
The PI3K-AKT-mTOR pathway is a network of intracellular signals involved in regulating cell growth, metabolism, survival and proliferation. Under normal physiological conditions, these signals help cells respond appropriately to nutrients, hormones and other environmental factors. In cancer, genetic alterations or abnormal pathway activity can cause cells to receive persistent growth and survival instructions.
Hormone receptor-positive, HER2-negative breast cancer is a particularly relevant setting because alterations affecting this pathway are common. Mutations involving PIK3CA and changes in related signaling components can contribute to cancer development and treatment resistance. Faeth estimates that approximately half of hormone receptor-positive, HER2-negative breast cancers exhibit relevant pathway abnormalities.
Patients with advanced disease may initially respond to endocrine treatment combined with CDK4/6 inhibitors, but resistance frequently develops. Tumors can adapt through several mechanisms, including changes in estrogen receptor signaling and activation of alternative growth pathways. The PI3K-AKT-mTOR network is one of the systems implicated in this process.
Several approved targeted medicines already address components of the pathway. Their clinical success establishes its importance, but individual treatments have limitations involving efficacy, adverse effects and resistance. These limitations provide the scientific rationale for investigating broader pathway suppression.
However, the presence of pathway abnormalities does not mean that every tumor is equally dependent on PI3K-AKT-mTOR signaling. The effectiveness of a new treatment may vary according to the genetic and biological characteristics of the cancer.
How does PIKTOR combine two medicines to inhibit three signaling nodes?
PIKTOR is an investigational combination regimen rather than one new chemical entity. It contains serabelisib, a selective PI3K-alpha inhibitor, and sapanisertib, an inhibitor of the mTORC1 and mTORC2 complexes. Both components are administered orally, creating a treatment strategy that can potentially be delivered without intravenous infusion.
Serabelisib targets PI3K-alpha, an enzyme involved in transmitting growth-related signals within cells. Sapanisertib acts on two mTOR complexes that regulate different aspects of cellular growth, protein synthesis and survival. Using the medicines together is intended to interfere with three connected signaling nodes.
The strategy addresses a problem encountered with inhibitors that block only one component of the pathway. Cancer cells may respond by activating compensatory signaling, allowing downstream activity to resume despite the presence of treatment. Inhibiting additional nodes could theoretically reduce this feedback reactivation.
However, more extensive pathway inhibition can also influence normal cells. PI3K and mTOR participate in metabolic and immune functions throughout the body, making toxicity an important consideration. A combination that produces stronger laboratory pathway suppression may not necessarily provide a better clinical therapeutic index.
Faeth is therefore investigating whether combining the two molecules at selected doses can deliver sufficient tumor inhibition while maintaining acceptable tolerability. The appropriate balance will need to be established in patients rather than inferred from the number of targets affected.
What will the ESMO 2026 poster establish about PIKTOR’s activity?
The presentation, abstract 431P, is scheduled for the Basic Science Poster Session on October 23 at ESMO 2026. It is titled Characterising the efficacy of multi-node PI3K/AKT/mTOR pathway inhibition with serabelisib and sapanisertib (PIKTOR) in combination with SERDs and CDK inhibitors in models of HR+/HER2- breast cancer. The research will be presented by Oliver Maddocks, Faeth’s co-founder and chief scientific officer.
The experiments examine PIKTOR as a standalone treatment and in combination with several endocrine and cell-cycle-targeting therapies. Faeth says the research includes measurements of pathway suppression, particularly involving AKT, together with outcomes in mouse xenograft models. These methods can help establish whether treatment influences cancer-associated signaling and tumor growth in experimental systems.
The company reports that PIKTOR suppressed key pathway components at levels comparable to or exceeding those observed with selected single-node inhibitors. However, the precise concentration ranges, effect sizes and statistical comparisons are not included in the October announcement. The forthcoming poster will be necessary to assess the magnitude and consistency of those findings.
Mouse xenograft models provide an opportunity to investigate drug combinations in living biological systems. However, the tumors and surrounding tissues do not fully reproduce the diversity of human breast cancer or the immune environment of patients. Drug exposure, metabolism and tolerability can also differ substantially between mice and people.
The results therefore provide a basis for further development rather than evidence that PIKTOR is clinically effective in breast cancer.
Why is the direct comparison with gedatolisib particularly relevant?
Gedatolisib is another investigational medicine targeting the PI3K-AKT-mTOR pathway. Unlike PIKTOR’s two-drug oral combination, gedatolisib is an intravenously administered inhibitor with activity across PI3K and mTOR signaling. Its development has provided additional clinical evidence supporting the value of multi-node inhibition in hormone receptor-positive breast cancer.
Faeth’s ESMO poster will compare PIKTOR directly with gedatolisib in two preclinical breast cancer xenograft models. Such experiments may help identify differences in tumor growth suppression under controlled laboratory conditions. However, the October announcement does not disclose which treatment performed better in those comparisons.
Gedatolisib has advanced into Phase 3 clinical development through Celcuity’s VIKTORIA-1 programme. In a PIK3CA-mutated advanced breast cancer population, Celcuity reported a median progression-free survival of 11.1 months for a gedatolisib-containing triplet, compared with 5.6 months for alpelisib plus fulvestrant. The hazard ratio was 0.50, indicating a statistically significant reduction in the measured risk of progression or death during the trial.
These clinical findings are relevant because they support the broader therapeutic concept of inhibiting multiple parts of the pathway. However, they do not establish that PIKTOR will produce comparable results. Different drug combinations, dosing schedules and patient characteristics can generate substantially different outcomes.
Likewise, a favorable PIKTOR result in mice would not establish clinical superiority over gedatolisib. That conclusion would require an appropriate comparison in human patients, taking account of both efficacy and safety.
Why is Faeth combining PIKTOR with endocrine treatments?
Hormone receptor-positive breast cancer frequently depends on estrogen receptor signaling to support tumor growth. Endocrine medicines interfere with that process through several mechanisms, including reducing estrogen production or degrading the receptor. However, tumors can develop resistance by activating alternative pathways.
Fulvestrant is a selective estrogen receptor degrader administered by intramuscular injection. It remains an important treatment component in selected advanced breast cancer settings and has been combined with several targeted medicines. Faeth’s preclinical experiments investigate whether adding PIKTOR can strengthen growth suppression in tumors exposed to endocrine treatment.
The research also includes oral selective estrogen receptor degraders. These medicines provide another strategy for reducing estrogen receptor signaling and may offer different administration characteristics. Their clinical roles vary according to the specific molecule, indication and regulatory status.
PIKTOR could theoretically complement endocrine therapy by blocking downstream growth signals that remain active after estrogen receptor inhibition. This combination strategy is scientifically plausible because hormone receptor and PI3K pathway signaling can interact. However, combining active medicines can also increase toxicity and drug interaction risks.
The ESMO experiments may provide information about which combinations demonstrate promising preclinical activity. They do not establish the optimal clinical regimen or prove that patients will experience longer progression-free survival.
What role do CDK inhibitors play in the proposed combinations?
CDK4/6 inhibitors are widely used with endocrine therapies for hormone receptor-positive, HER2-negative advanced breast cancer. They act on proteins involved in controlling the cell cycle, helping prevent malignant cells from progressing through critical stages of division. Their introduction has substantially changed treatment outcomes for eligible patients.
However, resistance eventually develops in many patients. Some cancers activate alternative growth signals or acquire molecular changes that reduce sensitivity to treatment. The PI3K-AKT-mTOR pathway is one possible contributor to this resistance.
Faeth’s preclinical programme investigates whether PIKTOR can complement CDK inhibition by acting on related but distinct processes supporting tumor growth. The combination could theoretically interfere with both cell-cycle progression and upstream growth signaling. However, the biological interactions may vary between cancer models.
Safety is particularly important when combining treatments affecting several cellular functions. CDK inhibitors can cause adverse effects involving blood counts and other organ systems, while PI3K and mTOR inhibition can produce metabolic and gastrointestinal toxicities. These risks must be evaluated carefully before pursuing more intensive combination regimens in patients.
The current ESMO announcement establishes that such combinations are being investigated experimentally. It does not announce a completed clinical trial demonstrating their safety or effectiveness.
How is the ongoing FTH-PIK-101 breast cancer trial designed?
The FTH-PIK-101 programme, registered as NCT07558733, is a Phase 1b/2 study evaluating PIKTOR in adults with hormone receptor-positive, HER2-negative advanced breast cancer. The first patient was dosed in April 2026, and Faeth expects to report initial clinical findings during 2027. The programme represents the transition from laboratory evidence to human testing in this indication.
The Phase 1b component focuses principally on safety and tolerability, including treatment-emergent adverse events and serious adverse events. Secondary outcomes include objective response rate, progression-free survival, overall survival, clinical benefit rate and duration of response. These measures may provide early evidence of activity while helping establish appropriate dosing.
The study’s objectives differ from those of the preclinical ESMO poster. Mouse tumor experiments are intended to inform biological and treatment-combination hypotheses, while the clinical trial must establish how the regimen behaves in people with advanced cancer. Findings from one cannot substitute for the other.
The company has not disclosed a confirmed objective response rate or mature progression-free survival result from the breast cancer trial. It would therefore be premature to describe PIKTOR as having demonstrated human breast cancer efficacy. The expected 2027 interim data represent an important forthcoming milestone.
What does the endometrial cancer programme contribute to PIKTOR’s development?
Faeth is also evaluating PIKTOR in the Phase 2 FTH-PIK-201 study involving patients with second-line advanced endometrial cancer. The company expects topline results before the end of 2026. The programme provides a separate clinical opportunity to investigate multi-node PI3K-AKT-mTOR inhibition in another malignancy where the pathway is frequently altered.
The primary endpoint is objective response rate, with secondary outcomes including progression-free survival, overall survival, clinical benefit rate and duration of response. Safety and tolerability are also central to the study. These endpoints will help determine whether the combination merits further development in endometrial cancer.
Experience from the endometrial programme may contribute useful information about drug exposure, dosing and adverse effects. However, treatment efficacy in one cancer cannot automatically establish effectiveness in another. Breast and endometrial cancers may share pathway alterations while differing substantially in disease biology.
Faeth has previously presented pharmacokinetic and pharmacodynamic modeling intended to explain its dose selection for the endometrial trial. Such research can help connect laboratory pathway suppression with drug exposure expected in patients. Nevertheless, the full clinical benefit-risk assessment must rely on patient outcomes.
The company therefore faces two distinct development milestones: a near-term Phase 2 readout in endometrial cancer and initial breast cancer data expected in 2027. Success in either indication would require interpretation according to its specific study design and endpoints.
How does Faeth’s public listing and financing support the programme?
Faeth became a publicly listed company through its combination with Sensei Biotherapeutics, completed in February 2026. The transaction was accompanied by approximately $200 million in gross proceeds from a private placement. The combined company adopted the Faeth Therapeutics name in June, with shares beginning to trade under the FTH ticker on Nasdaq on June 16.
The financing was intended to support development of PIKTOR and related corporate activities. It provided resources for the endometrial and breast cancer programmes as the company advanced clinical testing. However, the $200 million transaction amount should not be treated as its unchanged current cash balance.
Faeth’s strategy focuses on multi-node inhibition rather than a broad portfolio of unrelated therapeutic approaches. This concentration may help the company allocate resources to a defined scientific hypothesis. It also increases its dependence on the clinical performance of PIKTOR.
The October ESMO presentation could strengthen scientific interest in the programme, particularly if the detailed experiments show consistent activity across different breast cancer models and treatment combinations. However, preclinical results do not remove the need for further financing or guarantee commercial success.
Clinical trial execution, dose selection, treatment tolerability and the timing of data readouts will determine whether the company’s financial resources translate into meaningful development progress.
What must PIKTOR demonstrate to compete with established pathway inhibitors?
The central challenge is proving that inhibition of PI3K-alpha, mTORC1 and mTORC2 provides greater clinically meaningful benefit than existing treatment strategies. Stronger suppression of cellular signaling may support that objective, but patients ultimately need improved cancer outcomes with acceptable adverse effects. Laboratory pathway inhibition alone is insufficient.
An important consideration is metabolic toxicity. PI3K and mTOR signaling participate in normal glucose regulation and other physiological functions, meaning treatment can potentially cause hyperglycemia and related complications. Other possible concerns include gastrointestinal effects, skin reactions and treatment interruptions.
Combining two orally administered medicines may improve convenience relative to an intravenous regimen. However, an oral treatment is not inherently safer or more effective. Dosing frequency, tolerability, drug interactions and patient adherence all influence its practical value.
Future studies will also need to determine whether PIKTOR benefits patients across different molecular subgroups. Tumors with PIK3CA mutations may respond differently from those without such mutations, while other pathway abnormalities could influence treatment sensitivity. Biomarker analyses may help identify appropriate populations for later development.
The absence of human comparative data against gedatolisib or other pathway inhibitors remains a major limitation. Preclinical head-to-head studies may guide research priorities, but they cannot establish treatment superiority in clinical practice.
What should researchers watch at ESMO 2026 and beyond?
Faeth’s October 23 presentation will provide more detail about the magnitude of pathway suppression and tumor-growth inhibition observed in its laboratory and animal studies. The direct comparison with gedatolisib may be particularly informative about how the two approaches behave in the same experimental conditions. However, the relative performance results have not yet been disclosed in the October 19 announcement.
The combination experiments involving fulvestrant, oral estrogen receptor degraders and CDK inhibitors may also identify promising treatment strategies. These findings could inform future clinical cohorts, although each combination would require appropriate safety evaluation before broader testing. The experimental results should not be presented as established human outcomes.
For Faeth, the more consequential clinical milestones are approaching. Its endometrial cancer Phase 2 readout is anticipated before the end of 2026, followed by initial breast cancer results during 2027. Those studies will test whether the multi-node hypothesis translates into measurable treatment activity.
The ESMO announcement provides additional scientific context for an investigational programme addressing a well-established resistance mechanism in oncology. PIKTOR’s combination of serabelisib and sapanisertib is intended to suppress multiple connected signaling pathways, potentially limiting opportunities for cancer cells to reactivate growth after treatment.
The central question remains whether broader pathway inhibition delivers sufficiently greater antitumor benefit without unacceptable toxicity. Faeth’s preclinical research supports continued investigation, but its competitive position against approved therapies and more advanced investigational medicines will be determined by human clinical results rather than mouse-model comparisons.
