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Lilly's $2.5B bet on Scorpion's mutant-selective PI3Kalpha inhibitor is tracking as a win-in-progress: tersolisib posted a 23% response rate with a favorable hyperglycemia profile at ESMO 2025, earning a Phase 3 advance in first-line PIK3CA-mutant breast cancer, though the pivotal readout isn't due until 2029.
Lilly pads cancer drug pipeline with Scorpion deal gaining once-daily oral PI3K-alpha inhibitor that could address 30-40 percent of HR-positive breast cancer.
"This is an example of a target that we've been working on ourselves for years," said Daniel Skovronsky, the Lilly CSO, in an interview near the annual J.P.…
Phase 3, randomized, double-blind, placebo-controlled study of tersolisib (LY4064809/STX-478) + CDK4/6 inhibitor + endocrine therapy in treatment-naive…
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Eli Lilly acquired Scorpion Therapeutics' mutant-selective PI3Kalpha inhibitor program (lead asset STX-478) for up to $2.5 billion - $1 billion upfront plus up to $1.5 billion in regulatory and sales milestones - announced at JPM25 on January 13, 2025 and closed March 14, 2025. Lilly retained only the PI3Kalpha program; Scorpion's remaining assets were spun out into Antares Therapeutics (launched June 2025 with $177M). Post-close, Lilly renamed STX-478 tersolisib (development code LY4064809). Updated Phase 1/2 PIKALO-1 data presented at ESMO 2025 (Annals of Oncology LBA26; 204 patients as of July 7, 2025) showed a 23% objective response rate with tersolisib monotherapy in PIK3CA-mutant breast cancer and a tolerability profile (hyperglycemia ~31%) favorable versus wild-type-active PI3Kalpha inhibitors, supporting the mutant-selective differentiation thesis. Lilly advanced the asset to Phase 3: PIKALO-2 (NCT07174336), a randomized placebo-controlled study of tersolisib plus a CDK4/6 inhibitor and endocrine therapy in first-line HR+/HER2- PIK3CA-mutant advanced breast cancer (n=920), began recruiting December 22, 2025, with primary completion estimated May 2029.
STX-478 is a Phase 1/2 mutant-selective PI3Kalpha inhibitor designed to avoid wild-type toxicity; it competes across three MOA classes in PIK3CA-mutant advanced solid tumors. Pan-PI3Kalpha inhibitors (wild-type active): Piqray (alpelisib, Novartis) is the approved benchmark, FDA approved 2019 in HR+/HER2- PIK3CA-mutant advanced breast cancer per SOLAR-1 (NEJM 2019), with Novartis reporting roughly $500M 2023 sales; major toxicity burden includes hyperglycemia (~65%) and rash, limiting real-world persistence. Mutant-selective PI3Kalpha inhibitors (direct class competitors): Itovebi (inavolisib, Roche) FDA-approved 2024 in 1L HR+ PIK3CA-mutant breast cancer combined with palbociclib+fulvestrant per INAVO120 (NEJM 2024) - this is Lilly's most immediate commercial threat; RLY-2608 (Relay Therapeutics) in Phase 3 as a pan-mutant selective agent; LOXO-783 (Lilly's own prior asset) discontinued. AKT inhibitors (downstream pathway class): Truqap (capivasertib, AstraZeneca) FDA-approved 2023 in HR+ breast cancer with PIK3CA/AKT1/PTEN alterations per CAPItello-291; miransertib (ArQule/Merck) in overgrowth syndromes. Commercial threat for STX-478 is Itovebi's first-mover mutant-selective franchise positioning and Truqap's broader biomarker label; Lilly must demonstrate superior tolerability and CDK4/6 combinability to justify premium.
STX-478 enters the most contested biomarker-selected segment of HR+/HER2- metastatic breast cancer, competing across three MOA classes in PIK3CA-mutant patients (roughly 40% of HR+). Mutant-selective PI3Kalpha inhibitors (direct class): Itovebi (inavolisib, Roche) FDA-approved October 2024 in 1L HR+ PIK3CA-mutant mBC with palbociclib + fulvestrant based on INAVO120 (NEJM 2024) demonstrating roughly 15-month PFS versus 7 months for control - this is the first-mover commercial incumbent and most direct STX-478 threat; RLY-2608 (Relay Therapeutics, Phase 3 ReDiscover) targets a broader mutant profile. Pan-PI3Kalpha (wild-type-active) inhibitors: Piqray (alpelisib, Novartis) approved 2019 with fulvestrant per SOLAR-1; limited by hyperglycemia/rash tolerability and now commercially eclipsed by mutant-selective class. AKT inhibitors: Truqap (capivasertib, AstraZeneca) FDA-approved 2023 with fulvestrant in HR+ PIK3CA/AKT1/PTEN-altered mBC per CAPItello-291 (NEJM 2023); broader biomarker label enables some overlapping use. CDK4/6 + endocrine therapy backbone (upstream standard): Ibrance (palbociclib, Pfizer), Kisqali (ribociclib, Novartis ~$2.5B 2023), Verzenio (abemaciclib, Lilly ~$4.5B 2023) are the 1L foundation; STX-478 must plug into these regimens. Commercial threat: Itovebi's 1L head-start plus Lilly's own Verzenio franchise dependency creates cannibalization dynamics; STX-478 differentiation requires superior therapeutic index and breadth across PIK3CA mutation subtypes.
Eli Lilly completed $2.5B acquisition of Scorpion Therapeutics, gaining STX-478, a mutant-selective PI3Kalpha inhibitor for HR+/HER2- breast cancer.
Lilly renamed STX-478 tersolisib (LY4064809) and, following positive PIKALO-1 Phase 1/2 data at ESMO 2025 (23% monotherapy ORR in PIK3CA-mutant breast cancer), began the Phase 3 PIKALO-2 trial (NCT07174336) on Dec 22, 2025 in first-line HR+/HER2- PIK3CA-mutant advanced breast cancer (n=920). Asset advanced Phase 1/2 -> Phase 3, tracking toward the deal's regulatory/sales milestones.
STX-478 is differentiated PI3Ka inhibitor with best-in-class potential over Novartis's Piqray. Closed March 2025; mechanism validated, market large.
| Deal | Year | Value | Outcome |
|---|---|---|---|
| Eli Lilly and Company / Scorpion Therapeutics (this deal) | 2025 | $2.5B | 64 |
| Eli Lilly and Company / Boehringer Ingelheim GmbH | 2011 | $444M | 89 |
| Eli Lilly and Company / Loxo Oncology, Inc. | 2019 | $8.0B | 88 |
| Eli Lilly and Company / Applied Molecular Evolution Inc. | 2003 | $400M | 88 |
| Eli Lilly and Company / ICOS Corporation | 2006 | $2.3B | 87 |
| Eli Lilly and Company / Novartis Animal Health | 2014 | $5.4B | 70 |
| Eli Lilly and Company / Incyte Corporation | 2009 | $755M | 69 |
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