Two related approvals under Project Orbis formalize a new standard of care in PD-L1–positive and PD-L1–negative metastatic Triple-negative Breast Cancer (mTNBC), while an exploratory analysis of ASCENT-04/KEYNOTE-D19 suggests the clinical advantage of frontline sacituzumab govitecan persists long after most control-arm patients ultimately receive the same drug
Key Takeaways
- On June 24, 2026, the FDA approved sacituzumab govitecan-hziy (Trodelvy®; Gilead Sciences) for two first-line indications in triple-negative breast cancer (TNBC): as monotherapy and in combination with pembrolizumab (Keytruda®) for PD-L1–positive disease.
- The approvals were supported by the ASCENT-03 and ASCENT-04/KEYNOTE-D19 phase III trials.
- A new exploratory analysis of ASCENT-04/KEYNOTE-D19 shows that the benefit of frontline sacituzumab govitecan plus pembrolizumab persists even after most patients on the comparator arm crossed over to receive sacituzumab govitecan following progression.
- A leading biostatistician has questioned whether the endpoint used in that analysis, PFS2, is reliable enough to guide sequencing decisions.
On June 24, 2026, the U.S. Food and Drug Administration (FDA) approved sacituzumab govitecan-hziy (Trodelvy®, Gilead Sciences) for two distinct first-line indications in triple-negative breast cancer (TNBC), closing the loop on two phase 3 programs that had been closely watched since their initial presentations in 2025 and 2026.
The first indication, grounded in the ASCENT-03 trial (NCT05382299), authorizes sacituzumab govitecan as a single agent for adults with unresectable locally advanced or metastatic TNBC who are not candidates for PD-1 or PD-L1 inhibitor–based therapy. The second, based on the ASCENT-04/KEYNOTE-D19 trial (NCT05382286), authorizes sacituzumab govitecan in combination with pembrolizumab (Keytruda®, Merck & Co/MSD) — or with pembrolizumab and berahyaluronidase alfa-pmph (Keytruda Qlex®, Merck & Co/MSD) — for adults with unresectable locally advanced or metastatic TNBC whose tumors express PD-L1 at a combined positive score of 10 or higher, as determined by the PD-L1 IHC 22C3 pharmDx assay, developed by Agilent Technologies and approved by the FDA as a companion diagnostic.[1][2]
Both applications were reviewed under Project Orbis, the FDA Oncology Center of Excellence’s framework for concurrent international review, with participation from regulatory authorities in Australia, Israel, Brazil, Canada, and Switzerland; the agency completed its review a month ahead of its own goal date using the voluntary Assessment Aid submission process.[2] The recommended dose of sacituzumab govitecan in either setting is 10 mg/kg by intravenous infusion on days 1 and 8 of each 21-day cycle, continued until disease progression or unacceptable toxicity.
The prescribing information carries a boxed warning for diarrhea and neutropenia, with additional warnings for hypersensitivity and infusion reactions, nausea and vomiting, reduced UGT1A1 activity, and embryo-fetal toxicity — a profile consistent with SN-38-based cytotoxicity that will require proactive supportive care given the extended treatment durations now anticipated in the frontline setting.[2]
UGT1A1 refers to UDP-glucuronosyltransferase 1A1, a liver enzyme responsible for metabolizing and eliminating certain drugs, toxins, and bilirubin from the body. Patients with reduced UGT1A1 activity, a genetic trait present in a meaningful subset of the population, process SN-38 more slowly and are consequently at greater risk of severe neutropenia and gastrointestinal toxicity.[2]
A Heterogeneous Disease With a Persistent Unmet Need
Triple-negative breast cancer (TNBC) remains one of the most challenging and most malignant subtypes of breast cancer to treat. Far from a single entity, TNBC represents a heterogeneous group of diseases with distinct histologic, genomic, and immunologic features, unified primarily by their lack of expression of the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2).[4] That absence forecloses the endocrine- and HER2-targeted therapies that have transformed outcomes in other breast cancer subtypes, leaving cytotoxic chemotherapy as the historical mainstay despite its narrow therapeutic index and frequent toxicity.[5][4]
Although TNBC accounts for only about 15% of breast cancer diagnoses in the United States, it is responsible for a disproportionate share of breast cancer mortality, with a substantial proportion of patients ultimately developing distant metastatic disease.[5] Recent therapeutic advances have begun to shift that outlook, but a major unmet medical need persists.[6][7]
Over the past decade, several classes of targeted agents have entered the TNBC treatment landscape. Poly(ADP-ribose) polymerase inhibitors (PARPi) offer a genuinely targeted option, but only for the minority of patients carrying a pathogenic germline BRCA1 or BRCA2 variant.[6][7][8] Pembrolizumab remains the only PD-1 checkpoint inhibitor approved in combination with chemotherapy in the first-line setting, a therapeutic option for roughly 40% of patients whose tumors are PD-L1–positive.[6][7] Against that backdrop, antibody-drug conjugates (ADCs) — principally sacituzumab govitecan and fam-trastuzumab deruxtecan-nxki (Enhertu®, Daiichi Sankyo and AstraZeneca) — have emerged as among the most consequential therapeutic advances in the space, even though neither agent was developed exclusively for TNBC.
Trop-2: A Workable Therapeutic Window
Trop-2, a transmembrane glycoprotein involved in calcium signaling and epithelial cell regulation, is overexpressed in the large majority of TNBC tumors while remaining comparatively low in normal epithelial tissue. That differential expression pattern has made Trop-2 an attractive ADC target, and it underlies the design of sacituzumab govitecan, which pairs a humanized IgG1 kappa antibody with SN-38 — the active topoisomerase I–inhibiting metabolite of irinotecan — through a hydrolyzable linker. (Full construct details are available via the ADC Drugmap) This chemistry is intended to concentrate cytotoxic payload delivery within Trop-2–expressing tumor cells while limiting the systemic exposure associated with irinotecan-derived toxicity, particularly high-grade diarrhea.[13]
ASCENT-04/KEYNOTE-D19: The Primary Results
Sacituzumab govitecan’s role in previously untreated, PD-L1–positive metastatic TNBC was established in ASCENT-04/KEYNOTE-D19, a phase III trial that randomized 443 patients 1:1 to sacituzumab govitecan (10 mg/kg intravenously on days 1 and 8 of each 21-day cycle) plus pembrolizumab (200 mg on day 1, up to 35 cycles), or to investigator’s choice chemotherapy — single-agent paclitaxel, nab-paclitaxel, or gemcitabine plus carboplatin — plus pembrolizumab. Eligible patients had locally advanced, unresectable, or metastatic disease with a PD-L1 combined positive score of 10 or higher by the 22C3 assay; prior anti–PD-(L)1 exposure in the curative setting was permitted.[11]
By blinded independent central review, the trial’s primary endpoint of progression-free survival (PFS) significantly favored the sacituzumab govitecan combination, with a median of 11.2 months compared with 7.8 months for chemotherapy plus pembrolizumab (hazard ratio [HR], 0.65; 95% CI, 0.51–0.84; P < .001), a 35% reduction in the risk of progression or death. Confirmed objective response rate (ORR) was likewise higher with the ADC-containing regimen. Overall survival data remained immature at the time of the primary analysis.[9][10][11]
Why the Benefit May Outlast First Progression
A central complication in interpreting ASCENT-04/KEYNOTE-D19 has been its crossover design: patients on the chemotherapy-plus-pembrolizumab arm who progressed were eligible to receive sacituzumab govitecan through the study, and did so at a rate of roughly 81%. That pattern raised a practical question with direct bearing on how the data should be read — if most control-arm patients eventually receive the experimental drug anyway, does sequencing it earlier meaningfully change outcomes?
To address this, investigators reported an exploratory analysis of progression-free survival after the next line of treatment (PFS2) — the time from randomization to progression on subsequent therapy or death — along with time to first and second subsequent therapies, at the 2026 ASCO Annual Meeting. The analysis was presented by Kevin Kalinsky, MD, MS, FASCO, professor and director in the Division of Medical Oncology of the Department of Hematology and Medical Oncology at Winship Cancer Institute of Emory University, using the same March 2025 data cutoff as the primary results, corresponding to a median follow-up of approximately 14 months.[9][10]
Despite the high crossover rate, PFS2 continued to favor frontline sacituzumab govitecan plus pembrolizumab: median PFS2 was not reached in that arm versus approximately 21.0 months with chemotherapy plus pembrolizumab (HR, 0.67; 95% CI, 0.48–0.95), a 33% reduction in risk. PFS2 event-free rates were 71.9% versus 53.0% at 18 months and 63.7% versus 45.6% at 24 months. Median time to first subsequent therapy was 17.3 months with frontline sacituzumab govitecan versus 9.8 months with chemotherapy (HR, 0.59; 95% CI, 0.46–0.76), and median time to second subsequent therapy was not reached versus 21.0 months, respectively (HR, 0.82; 95% CI, 0.59–1.14). At data cutoff, 43% of patients were on frontline sacituzumab govitecan, compared with 23% on frontline chemotherapy.[9]
Treatment patterns after progression diverged sharply between arms. Among chemotherapy-arm patients who advanced to a subsequent line, the vast majority received sacituzumab govitecan, whereas patients who progressed on frontline sacituzumab govitecan more often received taxanes, platinum-based chemotherapy, or capecitabine (Xeloda®, Cheplapharm). No new safety signals emerged relative to the primary analysis, with the expected pattern of higher diarrhea rates on the ADC-containing arm and higher rates of anemia, thrombocytopenia, and peripheral neuropathy on chemotherapy.[9]
At the ASCO presentation, Kalinsky framed the durability of this effect, despite extensive crossover, as evidence that earlier use of sacituzumab govitecan confers a benefit that later-line administration does not fully replicate — potentially reflecting an additive or synergistic immunologic effect from combining an ADC with checkpoint blockade.[9][10]
A Statistical Counterpoint
Not every observer has viewed PFS2 as a reliable gauge of that benefit. Speaking as the analysis’s invited discussant at ASCO and in subsequent post-meeting commentary, Meredith M. Regan, ScD, a biostatistician and professor of medicine at Dana-Farber Cancer Institute and Harvard Medical School who was not involved in the trial, cautioned against relying on PFS2 to answer questions about first-line treatment sequencing.[9][12] She noted that the endpoint lacks a standardized definition across trials, is not incorporated into FDA benefit-risk frameworks for oncology approvals, and — given the heterogeneity of subsequent therapies received across both arms — does not cleanly isolate the treatment effect attributable to the frontline regimen itself.[10] Regan further indicated that existing evidence does not support PFS2 as a validated surrogate for overall survival in metastatic breast cancer, while allowing that a harmonized, cross-trial definition could eventually make the endpoint more informative.[9][12]
Where This Leaves Practice
The FDA’s June 2026 approvals settle, for now, the regulatory status of sacituzumab govitecan in first-line TNBC: full approval, not accelerated, applicable to both PD-L1–positive disease (in combination with pembrolizumab) and PD-L1–negative or checkpoint-ineligible disease (as monotherapy).
The PFS2 analysis adds a layer of clinical reassurance — tempered by legitimate methodological objection — that sequencing sacituzumab govitecan early, rather than reserving it for progression, is where its advantage is most fully realized. Confirmation will ultimately rest on the maturing overall survival data from ASCENT-04/KEYNOTE-D19, which remain the benchmark against which this expanded indication will continue to be judged.
Clinical Trials
Study of Sacituzumab Govitecan-hziy Versus Treatment of Physician’s Choice in Patients With Previously Untreated Locally Advanced Inoperable or Metastatic Triple-Negative Breast Cancer (ASCENT-03) — ClinicalTrials.gov ID NCT05382299
Study of Sacituzumab Govitecan-hziy and Pembrolizumab Versus Treatment of Physician’s Choice and Pembrolizumab in Patients With Previously Untreated, Locally Advanced Inoperable or Metastatic Triple-Negative Breast Cancer (ASCENT-04) — ClinicalTrials.gov ID NCT05382286
Highlights of Prescribing Information
Sacituzumab govitecan-hziy (Trodelvy®, Gilead Sciences) [Prescribing Information]
Fam-trastuzumab deruxtecan-nxki (Enhertu®; Daiichi Sankyo and AstraZeneca) [Prescribing Information]
Pembrolizumab (Keytruda®; Merck & Co/MSD) [Prescribing Information]
Pembrolizumab and berahyaluronidase alfa-pmph (Keytruda Qlex®; Merck & Co/MSD) [Prescribing Information]
Capecitabine (Xeloda®; Cheplapharm) [Prescribing Information]
References
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[2] U.S. Food and Drug Administration. FDA approves sacituzumab govitecan-hziy as monotherapy and in combination with pembrolizumab for first-line treatment of triple-negative breast cancer. June 24, 2026. Online. Last accessed on September 2, 2026.
[3] Szeląg-Pieniek S, Kucak J, Malinowski D, Oswald S, Droździk M, Kurzawski M. The Impact of UGT1A1 Genetic Variability on Enzyme Expression in Liver Pathology. Genes (Basel). 2026 May 21;17(5):589. doi: 10.3390/genes17050589. PMID: 42195046; PMCID: PMC13205437.
[4] Derakhshan F, Reis-Filho JS. Pathogenesis of Triple-Negative Breast Cancer. Annu Rev Pathol. 2022 Jan 24;17:181-204. doi: 10.1146/annurev-pathol-042420-093238. PMID: 35073169; PMCID: PMC9231507.
[5] American Cancer Society. Triple-negative breast cancer. Updated January 25, 2025. Online. Last accessed on September 2, 2026.[3] Li Y, Zhang H, Merkher Y, Chen L, Liu N, Leonov S, Chen Y. Recent advances in therapeutic strategies for triple-negative breast cancer. J Hematol Oncol. 2022 Aug 29;15(1):121. doi: 10.1186/s13045-022-01341-0. PMID: 36038913; PMCID: PMC9422136.
[7] Riaz F, Gruber JJ, Telli ML. New Treatment Approaches for Triple-Negative Breast Cancer. Am Soc Clin Oncol Educ Book. 2025 Jun;45(3):e481154. doi: 10.1200/EDBK-25-481154. Epub 2025 Jun 3. PMID: 40460322.
[8] El Gazzar WB, Albakri KA, Hasan H, Badr AM, Farag AA, Saleh OM. Poly(ADP-ribose) polymerase inhibitors in the treatment landscape of triple-negative breast cancer (TNBC). J Oncol Pharm Pract. 2023 Sep;29(6):1467-1479. doi: 10.1177/10781552231188903. Epub 2023 Aug 9. PMID: 37559370.
[9] Kalinsky K, Schmid P, de Azambuja E, Loi S, Kim SB, Yam C, Rapoport BL, Im SA, Pistilli B, McHayleh W, Cescon DW, Watanabe J, Lara A, Freitas-Junior R, Lortholary A, Caldwell K, Huo Y, Lai C, Tolaney SM. Progression-free survival after next line of treatment (PFS2) and subsequent therapies (subs tx) in the ASCENT-04 study of participants (pts) with previously untreated PD-L1+ metastatic triple-negative breast cancer (mTNBC) treated with sacituzumab govitecan (SG) plus pembrolizumab (pembro) vs chemotherapy (chemo) plus pembro. Presented at: 2026 ASCO Annual Meeting; May 29–June 2, 2026; Chicago, IL. J Clin Oncol 44, 2026 (suppl 17; abstr LBA1000).
[10] de Azambuja E, Kalinsky K, Loi S, Kim SB, Yam C, Rapoport BL, Im SA, Pistilli B, McHayleh W, Cescon DW, Watanabe J, Lara A, Freitas-Junior R, Bofill JS, Afshari M, Gary D, Wang L, Lai C, Schmid P. Sacituzumab govitecan (SG) + pembrolizumab (pembro) vs chemotherapy (chemo) + pembro in previously untreated PD-L1–positive advanced triple-negative breast cancer (TNBC): Primary results from the randomized phase 3 ASCENT-04/KEYNOTE-D19 study. J Clin Oncol. 2025;43(17_suppl):LBA109.
[11] Tolaney SM, de Azambuja E, Kalinsky K, Loi S, Kim SB, Yam C, Rapoport B, Im SA, Pistilli B, Mchayleh W, Cescon DW, Watanabe J, Bañuelas MAL, Freitas-Junior R, Salvador Bofill J, Afshari M, Gary D, Wang L, Lai C, Schmid P; ASCENT-04/KEYNOTE-D19 Clinical Trial Investigators. Sacituzumab Govitecan plus Pembrolizumab for Advanced Triple-Negative Breast Cancer. N Engl J Med. 2026 Jan 22;394(4):354-366. doi: 10.1056/NEJMoa2508959. PMID: 41564397.
[12] Haelle T. New Frontline Standard or Not? Triple-Negative Breast Cancer Data Spark Debate. Oncology News Central/Health Central. June 8, 2026. Online. Last accessed on September 2, 2026.
[13] Li T, Zhang T, Dang Y, et al. Trop2-based antibody-drug conjugates: emerging strategy and progress in triple-negative breast cancer therapy. Curr Oncol. 2026;33(2):92.
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