Clinical Outcomes of 130 Patients with Hormone Receptor-Positive and Human Epidermal Growth Factor Receptor 2-Negative Metastatic Breast Cancer Treated with Palbociclib plus Endocrine Therapy and Subsequent Therapy: A Real-World Single-Center Retrospective Study in China

Effectiveness and Safety of Palbociclib Plus Endocrine Therapy in Patients with Advanced Breast Cancer: A Multi-Center Study in China

BACKGROUND

Palbociclib has been approved for marketing in China. However, its effectiveness, safety, and latent variables in the Chinese population require further investigation.

METHODS

Information was retrieved from 397 patients with metastatic breast cancer (mBC) who received at least two cycles of palbociclib plus endocrine therapy (PAL plus ET) at eight clinical sites in China. The patients' demographic characteristics, treatment patterns, and adverse events (AEs) were analyzed.

RESULTS

The objective response rate (ORR) and clinical benefit rate (CBR) for PAL plus ET were 28.97% and 66.25%, respectively. The median PFS was 14.2 months in the whole population. In addition to protein Ki-67 status and sensitivity to ETs, no liver metastases, fewer metastatic sites, an earlier line of therapy, and treatment combined with AI instead of FUL were also considered as independent prognostic factors for PAL treatment. Administration of PAL was generally well tolerated in patients with hormone-receptor-positive and human-epidermal-growth-factor-receptor-2-negative (HR+/HER2-) advanced breast cancer (ABC). The therapy was safe in the elderly population, which is consistent with the outcomes of the whole population and previous reports.

CONCLUSIONS

In this most widely distributed study in China to date, palbociclib combined with ET proved its effectiveness for HR+/HER2- ABC treatment, and adverse events were manageable. Here, we identified some independent prognosis factors, but the mechanism by which these factors influence effectiveness requires further verification.

Place in Therapy of Cyclin-Dependent Kinase 4/6 Inhibitors in Breast Cancer: A Targeted Literature Review

Cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) are the preferred regimen for patients with hormone receptor-positive and human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced or metastatic breast cancer. However, the optimal treatment sequencing for CDK4/6i with other available therapeutic options is unclear. We conducted a targeted literature review to identify the current evidence on CDK4/6i treatment patterns in patients with breast cancer. The search was initially conducted in October 2021 and subsequently updated in October 2022. Biomedical databases and gray literature were searched, and bibliographies of included reviews were screened for relevant studies. The search identified ten reviews published since 2021 and 87 clinical trials or observational studies published since 2015. The included reviews discussed CDK4/6i usage with or without endocrine therapy (ET) in first-line and second-line treatment for patients with HR+/HER2- advanced or metastatic breast cancer, followed by ET, chemotherapy, or targeted therapy with ET. Clinical studies reported similar treatment sequences consisting of ET, chemotherapy, or targeted therapy with ET prior to CDK4/6i with ET, followed by ET monotherapy, chemotherapy, targeted therapy with ET, or continued CDK4/6i with ET. Current evidence suggests CDK4/6i are effective for HR+/HER2- advanced or metastatic breast cancer in earlier lines of therapy. Efficacy of CDK4/6i as measured by progression-free survival and overall survival was similar within a line of therapy regardless of the type of prior therapy. Survival on different post-CDK4/6i treatments was also similar within the same line of therapy. Additional research is needed to investigate the optimal place in therapy of CDK4/6i and the sequencing of treatments following progression on CDK4/6i.

Palbociclib plus endocrine therapy in hormone receptor-positive and HER2 negative metastatic breast cancer: a multicenter real-world study in the northwest of China

BACKGROUND

Real-world data of Palbociclib are insufficient in China. This study aimed to investigate the treatment pattern and real-world outcomes in hormone receptor positive and human epidermal growth factor 2 receptor negative (HR+/HER2-) metastatic breast cancer (MBC) patients treated with Palbociclib in the northwest of China.

METHODS

HR+/HER2- MBC patients who received Palbociclib in 8 centers from July 2017 to September 2019 were retrospectively included in this study. Real-world objective response rate (ORR), progression-free survival (PFS) and safety profiles were analyzed. The survival curves were plotted by the Kaplan-Meier method to analyze PFS, which was verified by the log-rank test.

RESULTS

In total, 211 women were eligible for the analysis. A total of 85 patients (40.3%), 78 (37.0%), and 48 (22.7%) received Palbociclib in the first-, second-, third- or later-line setting, respectively. 46 patients achieved partial response and 145 patients experienced stable disease, with an ORR of 21.8% and a disease control rate of 90.5%. Following a median follow-up period of 14.2 months, the median PFS was 12.2 months (95% confidence interval, 10.1-14.3 m), and the median overall survival was not reached. Early Palbociclib initiation, sensitivity or acquired resistance to endocrine therapy, estrogen receptor and progesterone receptor double positivity, less than 3 metastatic sites, without visceral metastasis, bone metastasis only, without prior chemotherapy or endocrine therapy were associated with a prolonged PFS in MBC (All P < 0.05). The most common grade 3 or 4 adverse events (AE) was neutropenia (36.5%), and the most common nonhematologic AE was fatigue (10.9%). No patient experienced AE leading to treatment discontinuation.

CONCLUSION

Palbociclib plus endocrine therapy exhibited favorable effectiveness and manageable toxicities in the real-world setting, supporting their use in Chinese patients with HR+/HER2 - MBC.

Early Application of Palbociclib Plus Endocrine Therapy in HR+/HER2- Metastatic Breast Cancer: A Better Choice Based on Data From the Chinese Population

Background: Palbociclib is the most widely used cyclin-dependent kinase 4/6 inhibitor in China, but its early application efficacy on Chinese metastatic breast cancer (MBC) patients was reported deficiently. Methods: Between February 2019 to December 2021, 95 female hormone receptor-positive (HR+)/human epidermal growth factor receptor-2 negative (HER2-) patients with MBC received palbociclib combined with AI or fulvestrant were retrospectively analyzed in our center. The primary outcome was progression-free survival (PFS). The objective response rate and clinical benefit rate (CBR) were evaluated. Results: The median follow-up period was 15 months (range from 2 to 37). Palbociclib performed superiorly when applicated in first-and-second line therapy than in later lines (P  =  .002). Palbociclib combined with AI or fulvestrant had a median PFS of 34 months (95% confidence interval [CI]  =  6.87-61.13) and 12 months (95%CI  =  7.76-16.24), respectively. Univariate subgroup analysis showed that the previous history of salvage chemotherapy (P  =  .015) and the presence of liver metastases (P < .001) significantly affected the efficacy of palbociclib. Despite the existence of liver metastases and primary endocrine resistance, which are two independent predictors of poor prognosis, early application of palbociclib in advanced stage can bring further benefits to these two groups of patients, rather than choosing salvage chemotherapy in the first place. Conclusion: Palbociclib combined with endocrine therapy has a favorable efficacy and acceptable toxicity in HR+/HER2- Chinese MBC patients. Better performance can be seen when palbociclib was applicated in the early stage.

Gallium-68 Labeling of the Cyclin-Dependent Kinase 4/6 Inhibitors as Positron Emission Tomography Radiotracers for Tumor Imaging

Cyclin-dependent kinase 4 and 6 (CDK4/6) have emerged as interesting therapeutic drug targets with many potential applications in anti-tumors, especially in breast cancer. A novel CDK4/6 kinase-derived positron emission tomography (PET) imaging agent was designed based on palbociclib modified with a chelator DOTA. This new compound with a chelator DOTA-palbociclib was radiolabeled with gallium 68 (⁶⁸Ga). After labeling, the purity and stability were evaluated, and the blood pharmacokinetics were carried out in normal healthy mice. Human breast cancer MCF-7 (ER+/HER2-) cells were used for in vitro cell uptake tests. PET imaging and ex vivo biodistribution were conducted in MCF-7 tumor-bearing mice. Specific binding of tumors was evaluated by the blocking assay. Furthermore, the uptake of ⁶⁸Ga-DOTA-palbociclib in tumors was studied by autoradiography of tissue sections followed by immunofluorescence evaluation of CDK4 and CDK6. ⁶⁸Ga-DOTA-palbociclib was synthesized very simply in a high labeling rate and radiochemical purity in 10 min. The labeling compound showed excellent stability both in vitro and in vivo and exhibited good pharmacokinetics, making it suitable for in vivo imaging. Cell uptake studies display that co-incubation with palbociclib can inhibit cellular uptake of ⁶⁸Ga-DOTA-palbociclib. In vivo imaging and ex vivo biodistribution in mice bearing MCF-7 tumors both showed obvious radioactive uptake in the tumor and higher tumor-to-muscle ratios, while the tumor radioactivity accumulation was significantly decreased when prior administered with an excess of cold palbociclib, confirming CDK4/6 specific binding of ⁶⁸Ga-DOTA-palbociclib in vivo. Autoradiography of the avid tumor section showed a high correlation between immunofluorescence with the CDK4/6 positive areas of the tumor, further demonstrating that ⁶⁸Ga-DOTA-palbociclib specifically targeted CDK4/6 positive tumors. We synthesized ⁶⁸Ga-DOTA-palbociclib, a new CDK4/6 kinase PET imaging agent, and validated its excellent stability, pharmacokinetics, and specific tumor binding. Based on our primary results, ⁶⁸Ga-DOTA-palbociclib is a promising imaging agent with the potential to tailor a precise treatment program for CDK4/6 inhibitors.