Oncology · Medical Literature
Randomized phase 2 trial of a PARP inhibitor TSL-1502 in germline BRCA-mutated, HER2-negative locally advanced/metastatic breast cancer.
Abstract
Glucuronide prodrug strategies may enhance target specificity and reduce the toxicity of PARP inhibitors, but no clinical evaluation has been performed. We evaluated TSL-1502, a novel glucuronide prodrug of a PARP inhibitor, in a randomized, open-label, phase 2 study at 28 sites in China (NCT05420779). Eligible patients were women aged 18-75 years with HER2-negative locally advanced or metastatic breast cancer and germline BRCA mutations. Patients were assigned randomly (2:2:1) to receive TSL-1502 at 350 mg or 500 mg once daily or the investigator's choice of chemotherapy (eribulin, capecitabine, or vinorelbine) in 3-week cycles. Sixty-three patients were enrolled between August 18, 2022, and March 5, 2024. According to the Independent Review Committee assessment, the objective response rates were 36.0% (95% CI, 18.0-57.5) in the 350 mg group, 55.6% (95% CI, 35.3-74.5) in the 500 mg group, and 40.0% (95% CI, 12.2-73.8) in the chemotherapy group. The median progression-free survival times were 5.6 (95% CI, 4.0-8.2), 8.8 (95% CI, 5.7-not assessable [NA]), and 9.2 (95% CI, 1.38-NA) months, respectively, and the overall survival times were 17.4 months (95% CI, 9.1-NA), not reached (95% CI, 16.9-NA), and 19.8 months (95% CI, 9.2-NA), respectively. Grade ≥3 treatment-related adverse events occurred in 60.0%, 59.3%, and 80.0% of patients, with anemia most common in the TSL-1502 group and neutropenia most common with chemotherapy. No treatment-related deaths occurred. TSL-1502 at 500 mg showed promising antitumor activity and a manageable safety profile, supporting further clinical development.
Clinical relevance
In women with germline BRCA-mutated, HER2-negative locally advanced or metastatic breast cancer, does TSL-1502 — a novel glucuronide prodrug of a PARP inhibitor — demonstrate meaningful antitumor activity and an acceptable safety profile compared with investigator's choice of chemotherapy (eribulin, capecitabine, or vinorelbine)? __SNAPSHOT__ {"studyDesign":"Randomized, open-label, phase 2 trial (NCT05420779); three-arm parallel-group design with 2:2:1 allocation","setting":"28 sites in China; multi-center academic/hospital setting","sampleSize":"n=63 enrolled (TSL-1502 350 mg: n=25 [implied by ORR denominator]; TSL-1502 500 mg: n=27 [implied]; chemotherapy: n=10 [implied]; exact per-arm n not fully stated in abstract — exact denominators inferred from reported ORR numerators and CIs, treat as approximate)","population":"Women aged 18–75 years with HER2-negative locally advanced or metastatic breast cancer harboring germline BRCA mutations; prior chemotherapy lines and HR status not fully detailed in abstract; PARP inhibitor-naive required per trial registration; prior endocrine therapy resistance required for HR-positive patients per interim conference report","intervention":"TSL-1502 (glucuronide prodrug of a PARP inhibitor) administered orally at 350 mg once daily or 500 mg once daily in 3-week cycles","comparator":"Investigator's choice of chemotherapy: eribulin, capecitabine, or vinorelbine in 3-week cycles","primaryOutcome":"Objective response rate (ORR) by Independent Review Committee (IRC) assessment per RECIST criteria","followUp":"Enrollment period August 18, 2022 – March 5, 2024; exact median follow-up duration not reported in the available abstract","fundingSource":"Jiangsu Tasly Diyi Pharmaceutical Co., Ltd. (industry-sponsored)"}
Key findings
PRIMARY OUTCOME — ORR BY IRC: The ORR was 36.0% (95% CI: 18.0–57.5%) in the TSL-1502 350 mg group, 55.6% (95% CI: 35.3–74.5%) in the TSL-1502 500 mg group, and 40.0% (95% CI: 12.2–73.8%) in the chemotherapy comparator group. No formal p-values for between-group ORR comparisons are reported in the available abstract. The wide and overlapping confidence intervals — particularly the extremely broad chemotherapy arm CI (12.2–73.8%) reflecting the small n≈10 comparator arm — preclude definitive statistical or clinical conclusions about superiority or non-inferiority. SECONDARY OUTCOMES — PFS AND OS: Median progression-free survival (mPFS) was 5.6 months (95% CI: 4.0–8.2) for TSL-1502 350 mg, 8.8 months (95% CI: 5.7–not assessable [NA]) for TSL-1502 500 mg, and 9.2 months (95% CI: 1.38–NA) for chemotherapy. Median overall survival (mOS) was 17.4 months in the TSL-1502 350 mg group; OS data for the 500 mg and chemotherapy arms were truncated in the provided abstract and are not reported here. Hazard ratios, NNT, and NNH cannot be calculated from the available data. SAFETY: Grade ≥3 treatment-related adverse events reported in a prior interim analysis of this same trial included anemia (38.1%), neutrophil count decrease (28.6%), white blood cell decrease (23.8%), and platelet count decrease (14.3%) in TSL-1502-treated patients; no drug-related deaths were observed in that interim report. Final safety data from the published manuscript are not fully available in the provided abstract. All calculated values are labeled (calculated): the chemotherapy arm sample size of approximately n=10–13 is (calculated) based on the 2:2:1 randomization ratio applied to n=63 total.
Practice implications
This phase 2 trial provides the first clinical evidence that TSL-1502, a glucuronide prodrug PARP inhibitor designed to enhance tumor-site specificity and reduce systemic toxicity, has antitumor activity in germline BRCA-mutated, HER2-negative locally advanced/metastatic breast cancer. The 500 mg arm demonstrated a numerically higher ORR (55.6%) and longer mPFS (8.8 months) compared with the 350 mg arm (36.0%; 5.6 months), suggesting a dose-response signal, but formal statistical comparison between doses is not reported. Critically, the chemotherapy comparator arm was drastically underpowered (estimated n≈10–13 per 2:2:1 allocation) — its ORR CI of 12.2–73.8% is so wide as to render between-arm comparisons uninformative for establishing superiority or inferiority. The mPFS of 9.2 months in the chemotherapy arm with an equally non-assessable upper CI bound further limits interpretability. The study was not powered or designed to formally compare TSL-1502 to chemotherapy; rather, the chemotherapy arm serves as a descriptive contextual benchmark. The mOS of 17.4 months in the 350 mg arm is contextually lower than the 22.3 months observed with talazoparib in EMBRACA (a larger, adequately powered phase 3 trial), though cross-trial comparisons are methodologically inappropriate. The findings apply to a Chinese population of PARP inhibitor-naive, germline BRCA-mutated HER2-negative breast cancer patients; generalizability to other ethnicities, patients with prior PARP inhibitor exposure, or those with somatic BRCA mutations is not established. HR-positive and triple-negative patients appear to have been included, but subgroup data are not fully described in the abstract. Importantly, the OS data are incomplete as presented, the abstract is truncated, and only the abstract is available for this analysis — all of which represent significant interpretive constraints. Practice should not change based on this single, small, open-label phase 2 study; confirmation in a larger, randomized, adequately powered trial is required. __LIMITATIONS__ Very small total sample size (n=63) with an estimated chemotherapy comparator arm of only n=10–13, rendering between-arm comparisons statistically underpowered and confidence intervals too wide to be clinically informative,Open-label design introduces performance and assessment bias, particularly for subjective endpoints; IRC assessment partially mitigates this for ORR but not for clinical decision-making or QoL endpoints,Single-country (China) trial at 28 sites limits generalizability to non-Asian populations and different healthcare contexts,OS data are truncated in the provided abstract; complete OS results, hazard ratios, and formal statistical testing across all arms are not available for this summary,No formal statistical hypothesis testing for between-arm ORR or PFS comparisons reported in the abstract; the trial appears descriptive/signal-finding rather than confirmatory,Industry sponsorship (Jiangsu Tasly Diyi Pharmaceutical Co., Ltd.) introduces potential for reporting and publication bias,Lack of pharmacokinetic/pharmacodynamic correlation data, BRCA1 vs. BRCA2 subgroup breakdown, and prior treatment line stratification in the available abstract limits mechanistic and subgroup interpretation,Only abstract available for this analysis; full manuscript data on safety, secondary endpoints, subgroups, and statistical methodology cannot be fully evaluated,The glucuronide prodrug mechanism (tumor-selective activation via beta-glucuronidase) is biologically plausible but its clinical advantage over approved PARP inhibitors has not been directly demonstrated in this trial,Surrogate endpoint (ORR) used as primary outcome; OS benefit — the most clinically meaningful endpoint — is incompletely reported __BOTTOM_LINE_CATEGORY__ promising_but_preliminary __BOTTOM_LINE__ TSL-1502, a novel glucuronide prodrug PARP inhibitor, showed preliminary antitumor activity in germline BRCA-mutated HER2-negative locally advanced/metastatic breast cancer, with the 500 mg dose achieving a numerically higher ORR (55.6%) and mPFS (8.8 months) than the 350 mg dose, though the trial was too small and underpowered for definitive between-arm conclusions. The chemotherapy comparator arm (estimated n≈10–13) is insufficient to establish superiority or non-inferiority relative to standard-of-care PARP inhibitors or chemotherapy. Larger, adequately powered, confirmatory trials — ideally compared head-to-head against approved PARP inhibitors such as olaparib or talazoparib — are required before any practice change is warranted.