Phase II sacituzumab govitecan ± pembrolizumab in HR+/HER2- metastatic breast cancer. The primary PFS endpoint was not met at ASCO 2024 (8.1 vs 6.2 mo, HR 0.81, p=0.37); the ESMO Breast 2026 final analysis (424RO, 34.6-mo follow-up) confirmed no significant ITT benefit (PFS HR 0.78, p=0.12; OS HR 0.97), with a numerical signal in the PD-L1+ (CPS ≥1) subgroup.
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Trial slides shared by KOLs at ASCO 2024 LBA1004. Click any image to expand. OCR text extracted via AWS Textract.
Highest-engagement tweets about this trial, ranked by KOL discussant count (replies + quote-tweets). Replies in green, quote-tweets in blue. Wall Street, stock-promo, and non-substantive replies excluded.
SACI-IO HR+: Adding pembrolizumab to SG did not improve PFS or OS overall in HR+ MBC, but a promising signal was seen in the PD-L1+ subgroup (CPS ≥1). More exploration needed. #ESMOBreast26 https://t.co/BLTrPHWVcn
Can we add pembrolizumab to SG for metastatic HR postive Her2 negative MBC? Not much benifit of PFS . 8.4 months vs 6.2 months . Not much useful strategy. @ASCO @OncoAlert #asco24 @Larvol https://t.co/quNLaziErI
SACI-IO HR+ in pts w/PDL1 unselected HR+ MBC, pembrolizumab + sacituzumab govitecan (SG) did not improve mPFS vs SG alone (8.1 vs 6.2 months, HR 0.81, p=0.37). a non-significant trend seen among patients w/ PD-L1+ (CPS ≥1) Larger trials ongoing #ASCO24 @OncoAlert https://t.co/
Ana garrida-castro presents Saci-IO in HR+ MBC. Intriguing trend towards improved PFS and OS in CPS+ disease with SG Pembo vs SG, underpowered for significance. HR neg study ongoing! #ASCO24 @OncoAlert https://t.co/pzs5Ccjsws
Ana Garrido-Castro from @DFCI_BreastOnc presents the results of SACI-IO HR+ investigator-initiated trial. Adding pembro to SG did not improve PFS in unselected pts with HR+ MBC (8.1 vs 6.2 mo, HR 0.81), although an intriguing trend in PFS and OS was seen in the PDL1+ subgroup. ht
#ASCO24 SACI-IO: SG w/wo Pembro in pts with metastatic HR+/HER2-BC 🔍≥1 prior ET and 0-1 ChT for MBC PFS➡️8.1 vs 6.2 mo (HR 0.76 but NS) OS➡️18.5 vs 17.9 mo (immature) Addition of Pembro to SG showed a non-significant trend toward improved PFS @OncoAlert https://t.co/Hf
SACI-IO HR+ is an investigator-initiated, multicenter, randomized Phase II trial evaluating whether the addition of pembrolizumab to sacituzumab govitecan (SG, anti-Trop-2 ADC) improves outcomes versus SG alone in patients with HR+/HER2- metastatic breast cancer who had received ≥1 prior endocrine therapy and 0–1 prior lines of chemotherapy. Primary results were reported at ASCO 2024 (LBA1004, Garrido-Castro), where the trial did not meet its primary endpoint: adding pembrolizumab did not significantly improve PFS in the PD-L1-unselected ITT population (8.1 vs 6.2 months; HR 0.81; p=0.37). Final results with extended follow-up were presented at ESMO Breast Cancer 2026 (Abstract 424RO, Garrido-Castro, 8 May 2026; data cutoff 3 December 2025, median follow-up 34.6 months), confirming no significant ITT benefit (PFS HR 0.78, p=0.12; OS HR 0.97), with the early suggestive OS trend (HR 0.65) maturing to essentially flat. A numerical, underpowered signal persisted in the exploratory PD-L1+ (CPS ≥1) subgroup.
Population: Adults with HR+ (ER ≥1% and/or PR ≥1%), HER2-negative, unresectable locally advanced or metastatic breast cancer. Prior endocrine therapy ≥1 line required. 0–1 prior chemotherapy lines for metastatic disease. Excluded: prior TOPO1-inhibitor ADCs, irinotecan, or PD-1/PD-L1 inhibitors. Baseline: median age 57, 77% prior CDK4/6 inhibitor, 56% no prior chemotherapy for metastatic disease.
Interventions: Arm A: Sacituzumab govitecan 10 mg/kg IV on Days 1 and 8 + pembrolizumab 200 mg IV on Day 1 of each 21-day cycle. Arm B: Sacituzumab govitecan 10 mg/kg IV on Days 1 and 8 of each 21-day cycle (monotherapy). Treatment continued until progression or unacceptable toxicity.
Endpoints: Primary: PFS in the overall population. Secondary: PFS in PD-L1+ (CPS ≥1 by 22C3); OS; ORR; safety. Exploratory: TROP2 / PD-L1 expression correlatives.
At the primary analysis (median follow-up 12.5 months), adding pembrolizumab to sacituzumab govitecan did not significantly improve PFS in the PD-L1-unselected ITT HR+/HER2- MBC population. Median PFS 8.1 vs 6.2 months; HR 0.81 (95% CI 0.51–1.28); p=0.37. Overall survival at this cut was not significant (HR 0.65, 95% CI 0.33–1.28). [ASCO 2024 LBA1004, Garrido-Castro; corroborated by @DrSGraff & @Dr_Oncologista slide OCR]
ITT population (N=52 vs N=52) at final analysis: median PFS 8.4 months (95% CI 4.5–12.5) with SG + pembrolizumab vs 6.7 months (95% CI 3.8–8.7) with SG alone; HR 0.78 (95% CI 0.52–1.19); p=0.12 (log-rank); PFS events 46 vs 45. Median OS 22.2 months (95% CI 17.3–31.2) vs 22.1 months (95% CI 18.0–27.4); HR 0.97 (95% CI 0.61–1.54); p=0.46 (log-rank); OS events 37 vs 36. ORR 21.2% vs 17.3% (ASCO 2024 cut). [ESMO Breast 2026 424RO, DCO 12/3/25, FU 34.6 mo]
PD-L1+ subgroup (CPS ≥1, N=39: 19 vs 20): median PFS 9.7 months (95% CI 4.2–15.7) vs 5.6 months (95% CI 2.5–8.7); HR 0.56 (95% CI 0.28–1.14); p=0.11 (log-rank); PFS events 17 vs 18. Median OS 24.3 months (95% CI 17.0–NR) vs 17.7 months (95% CI 12.4–33.0); HR 0.69 (95% CI 0.32–1.48); p=0.34 (log-rank); OS events 12 vs 15. Numerically favourable but underpowered; not statistically significant. [ESMO Breast 2026 424RO, DCO 12/3/25, FU 34.6 mo]
Data evolution note: between the ASCO 2024 preliminary cut (DCO 1/12/2024, median FU 9.2 months) and the ESMO Breast 2026 final analysis (DCO 12/3/2025, median FU 34.6 months), the ITT OS HR moved from 0.65 (suggestive trend) to 0.97 (essentially flat). PD-L1+ subgroup signals remained directionally consistent.
"The safety profile of SG plus pembrolizumab was similar to that expected with either agent and no new safety signals were reported." One Grade 5 TEAE was reported in the SG monotherapy arm: hepatic failure (n=1), unlikely related to SG per investigator-assessed attribution. [ESMO Breast 2026 424RO, DCO 12/3/25, FU 34.6 mo]
Treatment-Emergent AEs ≥15% (Grade ≥2 / Grade 3-4), SG + Pembrolizumab (N=52) vs SG (N=52):
Interpretation (ASCO 2024 primary + ESMO Breast 2026 final analysis): The primary endpoint was negative — adding pembrolizumab did not significantly improve ITT PFS (ASCO 2024: 8.1 vs 6.2 mo, HR 0.81, p=0.37; ESMO Breast 2026 final: HR 0.78, p=0.12). With mature 34.6-month follow-up, the ITT OS hazard ratio moved from an early 0.65 to 0.97 (p=0.46) — the suggestive trend did not bear out. The PD-L1+ (CPS ≥1) subgroup signal persists numerically (PFS HR 0.56, OS HR 0.69) but remains underpowered and not statistically significant. KOL commentary below reflects the ASCO 2024 data cut and should be read in that context.
Stephanie Graff reported the SACI-IO HR+ topline cleanly: “in pts w/PDL1 unselected HR+ MBC, pembrolizumab + sacituzumab govitecan (SG) did not improve mPFS vs SG alone (8.1 vs 6.2 months, HR 0.81, p=0.37),” while flagging “a non-significant trend seen among patients w/ PD-L1+ (CPS ≥1).” Hope Rugo framed the same data more permissively, noting an “Intriguing trend towards improved PFS and OS in CPS+ disease with SG Pembo vs SG, underpowered for significance,” with the companion “HR neg study ongoing.” Paolo Tarantino similarly described “an intriguing trend in PFS and OS… seen in the PDL1+ subgroup.” Abi Siva polled the implications directly — “promising signal was seen in the PD-L1+ subgroup (CPS ≥1). More exploration needed.” Yakup Ergün noted the “Addition of Pembro to SG showed a non-significant trend toward improved PFS.” Suyog Amol Akhade dissented on practicality, calling the SG+pembro PFS gain “Not much benifit” and the regimen not a useful strategy.