Oncology · Medical Literature
A Phase Ib Study of Chemoimmunotherapy with Pegylated Liposomal Doxorubicin and Pembrolizumab in Estrogen Receptor-Positive Metastatic Breast Cancer.
Abstract
Pegylated liposomal doxorubicin (PLD) is a potent immunogenic cell death inducer, allowing for improved tumor-immune recognition and T-cell activation. We report a phase Ib study of combined PLD and pembrolizumab (PEM) in estrogen receptor (ER)-positive/human epidermal growth factor receptor 2-negative metastatic breast cancer (MBC). Patients with MBC, who progressed on hormonal, biological, and cytotoxic chemotherapy, were eligible. Study objectives were safety, response, survival, and pharmacokinetics (PK). The study consisted of two cohorts: PLD 30 mg/m2 once every 3 weeks and PLD 40 mg/m2 once every 4 weeks, with PEM 200 mg once every 3 weeks in both cohorts. Responding and stable patients continued treatment until disease progression or intolerance. Thirty-five patients were enrolled and received a total of 201 PLD and 257 PEM treatments. Treatment was well tolerated with no significant neutropenia, no cardiac events, and minimal hair loss. Treatment-related serious adverse events were observed in three patients. In patients receiving >3 cycles, cutaneous toxicity often forced treatment delays. The disease control rate was 67%, including 10 responses with median duration of 11 months. Responses of large liver metastases were observed. The median overall survival was 25 months. PLD PK was monoexponential with high peak plasma concentration, long half-life (∼3 days), slow clearance, and small volume of distribution in the central compartment. PEM plasma levels indicated mean half-life of ∼11 days with high trough concentrations. Gene expression tumor profiling identified 16 genes upregulated in responders versus nonresponders, including interferon-stimulated genes. The combination of PLD with PEM is well-tolerated, active, and feasible for extended treatment with durable responses. The results suggest possible contribution of PEM to the antitumor effect. The combination of PLD and PEM in ER-positive MBC resulted in durable antitumor responses and median survival exceeding 2 years in a heavily pretreated patient group. These clinical observations together with the pharmacologic rationale and gene expression data have translational relevance supporting further exploration of combinations of nanomedicines with immunotherapy in this breast cancer population.
Clinical relevance
In patients with ER-positive/HER2-negative metastatic breast cancer who have progressed on hormonal, CDK4/6 inhibitor, and prior cytotoxic chemotherapy, is the combination of pegylated liposomal doxorubicin (PLD) and pembrolizumab (PEM) safe, feasible, and associated with meaningful disease control? __SNAPSHOT__ {"studyDesign":"Single-center, open-label, phase Ib dose-finding and safety study (two-cohort design); no randomization or control arm","setting":"Single academic center; country not explicitly stated in abstract (Israel, based on authorship and institutional affiliations); conducted over approximately 6 years","sampleSize":"n=35 (Cohort 1: n=15 [PLD 30 mg/m² Q3W]; Cohort 2: n=20 [PLD 40 mg/m² Q4W]); 201 total PLD administrations and 257 total PEM administrations received","population":"Adult women (age ≥18) with ECOG PS 0–2, pathologically confirmed ER-positive/HER2-negative stage IV breast cancer, who had progressed on hormonal therapy, CDK4/6 inhibitors, and up to three prior lines of cytotoxic chemotherapy","intervention":"PLD at two dose levels (30 mg/m² Q3W or 40 mg/m² Q4W) combined with pembrolizumab 200 mg flat dose Q3W in both cohorts; treatment continued until disease progression or intolerance","comparator":"Not applicable (single-arm study; no randomized control group)","primaryOutcome":"Safety (as a phase Ib study); secondary objectives included objective response, disease control rate, duration of response, overall survival, and pharmacokinetics","followUp":"Not explicitly reported in the abstract; study conducted over approximately 6 years at a single center","fundingSource":"Industry and non-profit — funded by Merck Sharp & Dohme LLC (a subsidiary of Merck & Co., Inc.) and by the Israel Cancer Association (grant #20160109); investigator-initiated study"}
Key findings
Among 35 heavily pretreated patients with ER+/HER2- MBC, the combination of PLD and PEM was well tolerated overall. Treatment-related serious adverse events (tr-SAEs) occurred in 3 of 35 patients (8.6%; absolute rate calculated). No significant neutropenia, cardiac events, or meaningful alopecia were reported — a favorable toxicity profile compared with conventional anthracycline regimens. The primary tolerability signal was cumulative cutaneous toxicity (palmar-plantar erythrodysesthesia/hand-foot syndrome), which frequently necessitated treatment delays in patients receiving more than 3 cycles. The disease control rate (DCR) was 67%, comprising 10 objective responses (ORR not separately reported as a percentage in the abstract; 10/35 = 28.6% [calculated]) with a median response duration of 11 months. Notable activity was observed in patients with large liver metastases. The median overall survival (mOS) was 25 months. No progression-free survival (PFS) data were separately reported in the abstract. Pharmacokinetic data showed PLD exhibits monoexponential kinetics with high peak plasma concentration, a long half-life (~3 days), slow clearance, and a small central volume of distribution; pembrolizumab demonstrated a mean half-life of approximately 11 days with high trough concentrations — a pharmacokinetic profile the authors describe as relatively concordant and potentially synergistic. Gene expression tumor profiling identified 16 genes upregulated in responders versus non-responders, including interferon-stimulated genes, representing a preliminary biomarker signal. Confidence intervals, p-values, hazard ratios, and NNT/NNH are not reported in the abstract.
Practice implications
This phase Ib study establishes a preliminary safety and feasibility signal for combining PLD with pembrolizumab in heavily pretreated ER+/HER2- MBC — a population with limited standard immunotherapy options. A DCR of 67% and a median response duration of 11 months in patients with prior hormonal, CDK4/6 inhibitor, and chemotherapy exposure are clinically noteworthy, particularly given the historically poor outcomes in this refractory setting. The reported mOS of 25 months appears notably longer than historical benchmarks for similarly pretreated endocrine-resistant ER+ MBC patients not receiving immunotherapy; however, this is an uncontrolled, single-arm comparison without matched historical cohorts and is subject to all the confounders inherent to single-arm phase Ib studies. The study does not establish that the combination is superior to PLD alone, pembrolizumab alone, or any other regimen — no causal attribution of benefit to the immunotherapy component is possible without a randomized comparator arm. Responses in patients with large liver metastases represent an intriguing and hypothesis-generating signal, as liver-dominant ER+ MBC remains a particularly challenging clinical scenario. Patients with earlier lines of therapy, TNBC, non-refractory ER+ disease, male sex, or significant comorbidities were not represented; generalizability is therefore limited. The biomarker findings (interferon-stimulated gene upregulation in responders) are exploratory and require prospective validation. As this summary is based on the published abstract and publicly available article text, additional granular data (subgroup analyses, specific toxicity grade distributions, PFS curves, cumulative dose-delay rates) may be available in the full manuscript. Practice should not change based on this study alone; rather, it provides the scientific rationale for a randomized phase II investigation. __LIMITATIONS__ Small sample size (n=35) severely limits statistical power and precision of all efficacy estimates,Single-center design conducted over 6 years introduces temporal heterogeneity in patient selection, supportive care, and concomitant therapies,No comparator arm: impossible to distinguish the contribution of PLD versus PEM versus their combination; observed OS cannot be attributed to immunotherapy synergy,Absence of randomization precludes control for selection bias and confounding (e.g., performance status, tumor burden, prior therapy sequencing),Comparison of mOS to historical controls is methodologically unreliable given differences in patient populations, era of treatment, and access to subsequent therapies,Surrogate endpoints (DCR, DOR) used without validated correlation to OS in this specific combination and population,No blinding (open-label), though less critical for objective radiographic endpoints,PFS not separately reported in the abstract, limiting characterization of the time-to-event efficacy profile,Biomarker analyses (gene expression profiling) are exploratory and hypothesis-generating only,Industry co-sponsorship by Merck (pembrolizumab manufacturer) represents a potential source of reporting or publication bias, though the study is described as investigator-initiated,Generalizability limited to patients meeting narrow eligibility criteria: heavily pretreated ER+/HER2- female patients with adequate performance status __BOTTOM_LINE_CATEGORY__ promising_but_preliminary __BOTTOM_LINE__ This phase Ib single-arm study demonstrates that the combination of pegylated liposomal doxorubicin and pembrolizumab is feasible and tolerable in heavily pretreated ER+/HER2- metastatic breast cancer, with a 67% disease control rate, a median response duration of 11 months, and a median overall survival of 25 months, including signals of activity in liver metastases. Cutaneous toxicity requiring treatment delays is the principal tolerability concern. These results are hypothesis-generating and should be considered insufficient to change practice; a prospective randomized phase II trial is required before this nanoimmunotherapy approach can be formally evaluated for clinical adoption.