Prognostic and predictive role of immune microenvironment in colorectal cancer

Colorectal cancer(CRC)represents a molecularly heterogeneous disease and one of the most frequent causes of cancer-related death worldwide.The traditional classification of CRC is based on pathomorphological and molecular character-istics of tumor cells(mucinous,ring-cell carcinomas,etc.),analysis of mechanisms of carcinogenesis involved(chromosomal instability,microsatellite instability,CpG island methylator phenotype)and mutational statuses of commonly altered genes(KRAS,NRAS,BRAF,APC,etc.),as well as expression signatures(CMS 1-4).It is also suggested that the tumor microenvironment is a key player in tumor progression and metastasis in CRC.According to the latest data,the immune microenvironment can also be predictive of the response to immune checkpoint inhibitors.In this review,we highlight how the immune environment influences CRC prognosis and sensitivity to systemic therapy.

A Th2-score in the tumor microenvironment as a predictive biomarker of response to Bacillus Calmette Guérin in patients with non-muscle invasive bladder carcinoma:A retrospective study

Intravesical Bacillus Calmette Guerin(BCG)is the gold standard therapy for intermediate/high-risk nonmuscle invasive bladder cancer(NMIBC).However,the response rate is~60%,and 50%of non-responders will progress to muscle-invasive disease.BCG induces massive local infiltration of inflammatory cells(Th1)and ultimately cytotoxic tumor elimination.We searched for predictive biomarker of BCG response by analyzing tumor-infiltrating lymphocyte(TIL)polarization in the tumor microenvironment(TME)in pre-treatment biopsies.Pre-treatment biopsies from patients with NMIBC who received adequate intravesical instillation of BCG(n=32)were evaluated retrospectively by immunohistochemistry.TME polarization was assessed by quantifying the T-Bet+(Th1)and GATA-3+(Th2)lymphocyte ratio(G/T),and the density and degranulation of EPX+eosinophils.In addition,PD-1/PD-L1 staining was quantified.The results correlated with BCG response.In most non-responders,Th1/Th2 markers were compared in pre-and post-BCG biopsies.ORR was 65.6%in the study population.BCG responders had a higher G/T ratio and a greater number of degranulated EPX+cells.Variables combined into a Th2-score showed a significant association with higher scores in responders(p=0.027).A Th2-score cut-off value>48.1 allowed discrimination of responders with 91%sensitivity but lower specificity.Relapse-free survival was significantly associated with the Th2-score(p=0.007).In post-BCG biopsies from recurring patients,TILs increased Th2-polarization,probably reflecting BCG failure to induce a pro-inflammatory status and,thus,a lack of response.PD-L1/PD-1 expression was not associated with the response to BCG.Our results support the hypothesis that a preexisting Th2-polarized TME predicts a better response to BCG,assuming a reversion to Th1 polarization and antitumor activity.

Laboratory scoring system to predict hepatic indocyanine green clearance ability during fluorescence imaging-guided laparoscopic hepatectomy

BACKGROUND Indocyanine green(ICG)fluorescence played an important role in tumor localization and margin delineation in hepatobiliary surgery.However,the preoperative regimen of ICG administration was still controversial.Factors associated with tumor fluorescence staining effect were unclear.AIM To investigate the preoperative laboratory indexes corelated with ICG fluorescence staining effect and establish a novel laboratory scoring system to screen specifical patients who need ICG dose adjustment.METHODS To investigate the predictive indicators of ICG fluorescence characteristics in patients undergoing laparoscopic hepatectomy from January 2018 to January 2021 were included.Blood laboratory tests were completed within 1 wk before surgery.All patients received 5 mg ICG injection 24 h before surgery for preliminary tumor imaging.ImageJ software was used to measure the fluorescence intensity values of regions of interest.Correlation analysis was used to identify risk factors.A laboratory risk model was established to identify individuals at high risk for high liver background fluorescence.RESULTS There were 110 patients who were enrolled in this study from January 2019 to January 2021.The mean values of fluorescence intensity of liver background(FI-LB),fluorescence intensity of gallbladder,and fluorescence intensity of target area were 18.87±17.06,54.84±33.29,and 68.56±36.11,respectively.The receiver operating characteristic(ROC)curve showed that FI-LB was a good indicator for liver clearance ability[area under the ROC curve(AUC)=0.984].Correlation analysis found pre-operative aspartate aminotransferase,alanine aminotransferase,gammaglutamyl transpeptidase,adenosine deaminase,and lactate dehydrogenase were positively associated with FI-LB and red blood cell,cholinesterase,and were negatively associated with FI-LB.Total laboratory risk score(TLRS)was calculated according to ROC curve(AUC=0.848,sensitivity=0.773,specificity=0.885).When TLRS was greater than 6.5,the liver clearance ability of ICG was considered as poor.CONCLUSION Preoperative laboratory blood indicators can predict hepatic ICG clearance ability.Surgeons can adjust the dose and timing of ICG preoperatively to achieve better liver fluorescent staining.

Recent advances in immunotherapy for hepatocellular carcinoma

Background:Treatment of hepatocellular carcinoma(HCC)is challenging as most patients are diagnosed at advanced stage with underlying chronic liver conditions.Conventional systemic chemotherapy has failed in HCC,and the clinical efficacy of FDA-approved molecular targeted agents such as sorafenib and lenvatinib remains unsatisfactory.Data sources:Literature search was conducted in Pub Med for relevant articles published before January 2021.The search aimed to identify recent developments in immune-based treatment approaches for HCC.Information of clinical trials was obtained from https://clinicaltrials.gov/.Results:Two immune checkpoint inhibitors(ICIs),nivolumab and pembrolizumab were approved as monotherapies,which has revolutionized HCC treatment.Besides,combination ICIs have also got accelerated FDA approval recently.Immune-based therapies have challenged targeted drugs owing to their safety,tolerability,and survival benefits.In addition to the significant success in ICIs,other immunotherapeutic strategies such as cancer vaccine,chimeric antigen receptor T-cells,natural killer cells,cytokines,and combination therapy,have also shown promising outcomes in clinical trials.Various diagnostic and prognostic biomarkers have been identified which can help in clinical decision making when starting treatment with ICIs.Conclusions:Immunotherapy has emerged as one of the mainstream treatment modalities for advanced HCC in recent years.However,challenges such as low response rate and acquired resistance in previously respondent patients still exist.Further research is needed to understand the unique resistance mechanism to immunotherapy and to discover more predictive biomarkers to guide clinical decision making.

Implications of the autophagy core gene variations on brain metastasis risk in non-small cell lung cancer treated with EGFR-TKI

Objective The brain is the main site of failure in cancer patients with epidermal growth factor receptor(EGFR)mutations undergoing treatment.However,identifying patients who may develop brain metastases(BM)is difficult.Autophagy is critical for cancer initiation and progression.We hypothesized that genetic variants in autophagy core genes might contribute to BM risk of non-small cell lung cancer(NSCLC)following treatment with EGFR tyrosine kinase inhibitor(EGFR-TKIs).Methods We systematically examined 16 potentially functional genetic polymorphisms in seven autophagy core genes among 105 TKI-treated NSCLC patients.Kaplan-Meier curves were plotted to assess the cumulative BM probability.Univariate and multivariate Cox proportional hazard regression analyses were utilized to calculate hazard ratios(HRs)and 95%confidence intervals(CIs).We evaluated the potential associations of these genes with subsequent BM development.Results We found that ATG16L1:rs2241880,ATG10:rs10036653,rs3734114,and ATG3:rs7652377 are significantly associated with NSCLC treated with EGFR-TKIs(all P<0.05).BM developed more often in patients with ATG3 rs7652377 CC genotype(33%),ATG10 rs10036653 AA genotype(43%),ATG10:rs3734114 CT/CC genotype(46%),and ATG16L1 rs2241880 AA genotype(37%)compared to patients with AA genotypes at rs7652377(12%),AT/TT genotypes at rs10036653(16%),the TT genotype at rs3734114(13%),or AG/GG genotypes at rs2241880(17%).Conclusion These associations may be critical for understanding the role of autophagy in BM risk.Future prospective studies are needed to determine if prophylactic cranial irradiation(PCI)could offer a survival benefit in this group of patients.

Refractory case of ulcerative colitis with idiopathic thrombocytopenic purpura successfully treated by Janus kinase inhibitor tofacitinib:A case report

BACKGROUND Concomitant ulcerative colitis (UC) and idiopathic thrombocytopenic purpura(ITP) is a rare phenomenon. The management of UC with ITP can be challenging,since a decreased platelet count augments UC.CASE SUMMARY A 24-year-old man with UC and steroid-resistant ITP experienced UC flare.Although continuous infusion of cyclosporine was initiated, UC did not improve.The administration of tofacitinib subsequently led to the induction of remission.The patient has maintained remission of UC and ITP for over one year ontofacitinib treatment. Whole transcriptomic sequencing was performed forinflamed rectal mucosae obtained before and after the initiation of Janus kinase(JAK) inhibitor, suggesting that distinct molecular signatures seemed to beregulated by JAK inhibitors and other conventional therapies including tumornecrosis factor lockers.CONCLUSION Tofacitinib should be considered in refractory cases of UC with ITP.

Potential new applications of immunotherapy for neuroendocrine neoplasms:immune landscape,current status and future perspectives

Neuroendocrine neoplasms(NENs)are a highly heterogeneous class of tumors arising from neuroendocrine cells and peptidergic neurons.After failure of first-line treatment,patients have poor prognosis and limited treatment options.Immune checkpoint inhibitors(ICIs)may be a powerful means of increasing therapeutic efficacy for such patients,but ICIs alone have low response rates and short disease control durations in most NENs and may be effective for only a portion of the population.ICIs combined with other immunotherapies,targeted therapies,or cytotoxic drugs have achieved some efficacy in patients with NENs and are worthy of further exploration to assess their benefits to the population.In addition,accumulating experimental and clinical evidence supports that the interaction between neuroendocrine and immune systems is essential to maintain homeostasis,and assessment of this broad neuroendocrine-immune correlation is essential for NEN treatment.In this review,we summarize the immune microenvironment characteristics,advances in immunotherapy,predictive biomarkers of ICI efficacy for NENs,and the effects of common endocrine hormones on the immune system,highlighting possible new application areas for this promising treatment in neglected NENs.

Long survival after immunotherapy plus paclitaxel in advanced intrahepatic cholangiocarcinoma: A case report and review of literature

BACKGROUND Intrahepatic cholangiocarcinoma(iCCA)is the second most common primary hepatic malignancy worldwide.However,currently available systemic therapies are of limited effectiveness,and the median overall survival of patients treated with first-line standard chemotherapy is less than one year.Immune checkpoint inhibitors have been used to treat solid tumors.Clinical studies recently explored the combination of chemotherapy and immunotherapy for CCA.However,the clinical significance of predictive biomarkers for chemo-immunotherapy in CCA remains unclear.It is also worth exploring whether a combination of chemotherapeutic agents can increase the sensitivity of CCA immunotherapy.CASE SUMMARY This study reports a case of advanced iCCA in which clinical complete remission had been achieved using a programmed death 1(PD-1)inhibitor and paclitaxel without known predictive biomarkers,but with BRCA1,KRAS,and NTRK3 mutations after rapid progression to first-line chemotherapy,and has remained in clinical complete remission for more than two years.This case suggests that chemo-immunotherapy is a potential therapeutic option for patients with iCCA and few known predictive biomarkers for immunotherapies as well as synergistic effect of the combination of paclitaxel and PD-1 monoclonal antibody.CONCLUSION The combination of paclitaxel and PD-1 monoclonal antibodyr can be explored in patients with advanced iCCA.

Final Results of a Phase II Study of Bevacizumab, Cisplatin and Pemetrexed as First-Line Therapy for Patients with Advanced Non-Squamous Non-Small Cell Lung Cancer

Background: Efficacy and safety data for cisplatin and pemetrexed plus bevacizumabinnon squamousnon non-small cell lung cancer (NSCLC) are still limited. Nevertheless, either bevacizumab plus platinum doublet or pemetrexed plus platinum is approved options for first line therapy. Predictive factors for bevacizumab are needed. KRAS is one of the most common oncogenic drivers in lung cancer. Its prognostic and predictive value in NSCLC is under investigation. Patients and methods: This trial evaluates the addition of bevacizumab 7.5 mg/kg to cisplatin 75 mg/m2 plus pemetrexed 500 mg/m2 as first line treatment in stage IV non-squamous NSCLC patients. Maintenance bevacizumab was received as monotherapy until progressive disease, unacceptable toxicityor consent with drawal. The primary objective was progression free survival (PFS). Secondary objectives included overall survival (OS), safety, global objective responses and the determination of KRAS mutation at baseline. Results: From March 2009 to March 2012, 31 patients were enrolled. Mean age was 59.19 (standard deviation (SD) 8.53). From all the patients included in this trial, 67.70% were men. KRAS was wild type in 19 patients (58.06%);in 7 (22.58%) was mutated and was unknown in 6 patients (19.35%). Median PFS for KRAS mutated patients was 4 months, whereas for the KRAS wild type it was 7.9 months (P = 0.0031). Median OS was 4 months for the KRAS population, and 16.1 months for the KRAS wild type (P = 0.0032). Twenty four patients (77.42%) experienced at least a grade 3 - 4 adverse event. The most common grade 3 - 4 toxicity was asthenia. Conclusions: Both PFS and OS were statistically longer for the KRAS wild type patients compared with the KRAS mutated population (P = 0.0031). Median OS was shorter than the reported in previous trials with bevacizumab. Nevertheless, focussing on the OS for KRAS wild type patients, this achieves a result or 16.1 months. Therefore, this would be a consistent data supporting to qualify this parameter as a predictive factor before starting treatment for NSCLC.

Exploitation of Gene Expression and Cancer Biomarkers in Paving the Path to Era of Personalized Medicine

Cancer therapy agents have been used extensively as cytotoxic drugs against tissue or organ of a specific type of cancer. With the better understanding of molecular mcchanislns undcrlying carcinogenesis and cellular events during cancer progression and metastasis, it is now possible to use targeted therapy for these molecular events. Targeted therapy is able to identify cancer patients with dissimilar genetic defects at cellular level for the same cancer type and consequently requires individualized approach for treatment. Cancer therapy begins to shill steadily from the tra- ditional approach of ＂one regimen for all patients＂ to a more individualized approach, through which each patient will be treated specifically according to their specific genetic defects. Personalized medicine accordingly requires identification of indicators or markers that guide in the decision mak- ing of such therapy to the chosen patients for more effective therapy. Cancer biomarkcrs are fre- quently used in clinical practice for diagnosis and prognosis, as well as identification ol responsive patients and prediction of treatment response of cancer patient. The rapid breakthrough and development of microarray and sequencing technologies is probably the main tool for paving the way toward ＂individualized biomarker-driven cancer therapy＂ or ＂personalized medicine＂. In this review, we aim to provide an updated knowledge and overview of the currcnt landscape of cancer biomarkers and their role in personalized medicine, emphasizing the impact of gcnomics Oil the implementation of new potential targeted therapies and development of novel cancer biomarkers in improving the outcome of cancer therapy.

An integrative approach of digital image analysis and transcriptome profiling to explore potential predictive biomarkers for TGFβblockade therapy

Increasing evidence suggests that the presence and spatial localization and distribution pattern of tumor infiltrating lymphocytes(TILs)is associate with response to immunotherapies.Recent studies have identified TGFβactivity and signaling as a determinant of T cell exclusion in the tumor microenvironment and poor response to PD-1/PD-L1 blockade.Here we coupled the artificial intelligence(AI)-powered digital image analysis and gene expression profiling as an integrative approach to quantify distribution of TILs and characterize the associated TGFβpathway activity.Analysis of T cell spatial distribution in the solid tumor biopsies revealed substantial differences in the distribution patterns.The digital image analysis approach achieves 74%concordance with the pathologist assessment for tumor-immune phenotypes.The transcriptomic profiling suggests that the TIL score was negatively correlated with TGFβpathway activation,together with elevated TGFβsignaling activity observed in excluded and desert tumor phenotypes.The present results demonstrate that the automated digital pathology algorithm for quantitative analysis of CD8 immunohistochemistry image can successfully assign the tumor into one of three infiltration phenotypes:immune desert,immune excluded or immune inflamed.The association between“cold”tumor-immune phenotypes and TGFβsignature further demonstrates their potential as predictive biomarkers to identify appropriate patients that may benefit from TGFβblockade.

Biomarkers of resistance to immune checkpoint inhibitors in non-small-cell lung cancer:myth or reality?

Immune checkpoint inhibitors represent a major therapeutic advance in non-small-cell lung cancer with several approved anti-programmed death-1 and anti-programmed death-L1 immunotherapies.A majority of patients however,will not respond to immune checkpoint inhibitors and display primary resistance while a subset of initially responsive patients will present secondary resistance.Thus,there is a crucial need for biomarkers to enable better prediction and diagnosis,and to overcome such resistance.Along with improvement in the understanding of immune escape,new biomarkers are being developed,including large scale proteomic,genomic and transcriptomic approaches in tumor and blood samples.We review the novel biomarkers that have been investigated in non-small-cell lung cancer and discuss how they can rationalize therapeutic strategies.

Resistance to antibody-drug conjugates in breast cancer:mechanisms and solutions

Antibody-drug conjugates(ADCs)are a rapidly developing therapeutic approach in cancer treatment that has shown remarkable activity in breast cancer.Currently,there are two ADCs approved for the treatment of human epidermal growth factor receptor 2-positive breast cancer,one for triple-negative breast cancer,and multiple investigational ADCs in clinical trials.However,drug resistance has been noticed in clinical use,especially in trastuzumab emtansine.Here,the mechanisms of ADC resistance are summarized into four categories:antibodymediated resistance,impaired drug trafficking,disrupted lysosomal function,and payload-related resistance.To overcome or prevent resistance to ADCs,innovative development strategies and combination therapy options are being investigated.Analyzing predictive biomarkers for optimal therapy selection may also help to prevent drug resistance.

The cutting-edge progress of immune-checkpoint blockade in lung cancer

Great advances in immune checkpoint blockade have resulted in a paradigm shift in patients with lung cancer.Immune-checkpoint inhibitor(ICI)treatment,either as monotherapy or combination therapy,has been established as the standard of care for patients with locally advanced/metastatic non-small cell lung cancer without EGFR/ALK alterations or extensive-stage small cell lung cancer.An increasing number of clinical trials are also ongoing to further investigate the role of ICIs in patients with early-stage lung cancer as neoadjuvant or adjuvant therapy.Although PD-L1 expression and tumor mutational burden have been widely studied for patient selection,both of these biomarkers are imperfect.Due to the complex cancer-immune interactions among tumor cells,the tumor microenvironment and host immunity,collaborative efforts are needed to establish a multidimensional immunogram to integrate complementary predictive biomarkers for personalized immunotherapy.Furthermore,as a result of the wide use of ICIs,managing acquired resistance to ICI treatment remains an inevitable challenge.A deeper understanding of the underlying biological mechanisms of acquired resistance to ICIs is helpful to overcome these obstacles.In this review,we describe the cutting-edge progress made in patients with lung cancer,the optimal duration of ICI treatment,ICIs in some special populations,the unique response patterns during ICI treatment,the emerging predictive biomarkers,and our understanding of primary and acquired resistance mechanisms to ICI treatment.

Emerging predictors of the response to the blockade of immune checkpoints in cancer therapy

Checkpoint blockade-based immunotherapy offers new options and powerful weapons for the treatment of cancer,but its efficacy varies greatly among different types of cancer and across individual patients.Thus,the development of the right tools that can be used to identify patients who could benefit from this therapy is of utmost importance in order to maximize the therapeutic benefit,minimize risk of toxicities,and guide combination approaches.Multiple predictors have emerged that are based on checkpoint receptor ligand expression,tumor mutational burden,neoantigen and microsatellite instability,tumor-infiltrating immune cells,and peripheral blood biomarkers.In this review,we discuss the current state and progress of predictors as aids in checkpoint blockadebased immunotherapy in cancer.

用于预测食管癌新辅助治疗反应的转录组学生物标志物

食管癌是一种预后较差的致死性疾病,其死亡率排在恶性肿瘤第六位。证据表明,对于可手术切除的食管肿瘤,新辅助化疗和放化疗可以改善生存。遗憾的是,只有15%-30%的患者对新辅助治疗有反应,且常出现毒性反应。目前临床上尚无有效的预测标志物,无法对患者进行个体化治疗以显著改善疗效。本文对用于预测食管癌新辅助治疗反应的生物标志物的当前进展进行综述,并对生物标志物的研发所面临的挑战展开讨论。我们将这些问题与对生物标志物开发和报道的建议相联系进行探讨。目前大多数生物标志物研究集中在mRNA和miRNA,这些研究报道了涉及多条信号通路和生物学过程的诸多不同基因,很大程度上是由于不同的研究平台和不同的分析方法造成的。而且许多研究也因过于薄弱,不足以鉴定出可能的生物标志物。尽管多种食管癌分子亚型被提出,但其与临床结局的关系我们知之甚少。我们预测,未来几年随着基因组数据与临床试验协作研究成果的不断积累,对食管癌患者进行分层从而实现个体化治疗将成为可能。我们建议,未来生物标志物的研发应融入到精心设计的回顾性和前瞻性临床研究中。

Pretreatment inflammatory indices predict Bevacizumab response in recurrent Glioma

Aim:It remains unclear what the best therapeutic option for recurrent glioma patients after Stupp treatment is.Bevacizumab(BVZ)is commonly administered in progression,but it appears that only some patients benefit.It would be useful to find biomarkers that determine beforehand who these patients are.Methods:The protocol included 31 high-risk progressing glioma patients after Stupp treatment who received BVZ 5-10 mg/kg every 14 days and temozolomide(3-19 cycles,150-200 mg five days each 28-day cycle)during a mean of eight cycles of BVZ or until tumor progression or unacceptable toxicity.We analyzed the clinical outcome values of inflammatory indices measured before BVZ administration.Results:Lymphocyte level before BVZ administration was the best independent predictor of overall survival(HR=0.34;95%CI:0.145-0.81;P=0.015).The area under the receiver operating characteristic(ROC)curve was 0.823,with 1.645 being the optimal cut-off value,and 0.80 and 0.85 the sensitivity and specificity values,respectively.Responder and non-responder survival curves were also significantly different,considering the first and second tertiles as cut-off points.The number of BVZ cycles was not related to lymphopenia.Pretreatment neutrophil platelet levels,platelet-to-lymphocyte ratio(PLR),and neutrophil-to-lymphocyte ratio(NLR)did not have independent predictive value.Inflammatory variables were not correlated with each other.However,patients with high NLR and PLR simultaneously(double positive PLR-NLR)showed a worse clinical outcome than the rest(P=0.043).Conclusion:Pretreatment lymphocyte levels and double positive PLR-NLR could be used as non-invasive hematological prognostic markers for recurrent gliomas treated with bevacizumab.A close relationship emerged between inflammation and angiogenesis.

Current status and progress in immunotherapy for malignant pleural mesothelioma

Malignant pleural mesothelioma(MPM)is a rare and aggressive malignant disease.Currently,the platinum doublet of pemetrexed and cisplatin is the standard first-line treatment for unresectable MPM.However,recent promising results of immunotherapy have markedly changed the landscape of MPM treatment.Further,the ongoing innovative therapeutic strategies are expected to expand the range of treatment options;however,several questions remain unanswered.First,establishing predictive biomarkers with high potency is urgently needed to optimize the patient selection process.Second,further exploration of the combination algorithm is expected to unveil more effective and safe regimens.Moreover,other dilemmas,such as the resistance mechanism of immunotherapy and the role of immunotherapy in perioperative settings,still warrant further exploration.

Using circulating tumor cells to advance precision medicine in prostate cancer

The field of circulating tumor cell(CTC)enrichment has seen many emerging technologies in recent years,which have resulted in the identification and monitoring of clinically relevant,CTC-based biomarkers that can be analyzed routinely without invasive procedures.Several molecular platforms have been used to investigate the molecular profile of the disease,from high throughput gene expression analyses down to single cell biological dissection.The established presence of CTC heterogeneity nevertheless constitutes a challenge for cell isolation as the several subpopulations can potentially display different molecular characteristics;in this scenario,careful consideration must be given to the isolation approach,whereas methods that discriminate against certain subpopulations may result in the exclusion of CTCs that carry biological relevance.In the context of prostate cancer,CTC molecular interrogation can enable longitudinal monitoring of key biological features during treatment with substantial clinical impact,as several biomarkers could predict tumor response to AR signaling inhibitors(abiraterone,enzalutamide)or standard chemotherapy(taxanes).Thus,CTCs represent a valuable opportunity to personalize medicine in current clinical practice.

Liquid biopsies to predict CDK4/6 inhibitor efficacy and resistance in breast cancer

Cyclin-dependent kinase 4 and 6(CDK4/6)inhibitors combined with endocrine therapy have transformed the treatment of estrogen receptor-positive(ER+)and human epidermal growth factor receptor 2 negative(HER2-)metastatic breast cancer.However,some patients do not respond to this treatment,and patients inevitably develop resistance,such that novel biomarkers are needed to predict primary resistance,monitor treatment response for acquired resistance,and personalize treatment strategies.Circumventing the spatial and temporal limitations of tissue biopsy,newly developed liquid biopsy approaches have the potential to uncover biomarkers that can predict CDK4/6 inhibitor efficacy and resistance in breast cancer patients through a simple blood test.Studies on circulating tumor DNA(ctDNA)-based liquid biopsy biomarkers of CDK4/6 inhibitor resistance have focused primarily on genomic alterations and have failed thus far to identify clear and clinically validated predictive biomarkers,but emerging epigenetic ctDNA methodologies hold promise for further discovery.The present review outlines recent advances and future directions in ctDNA-based biomarkers of CDK4/6 inhibitor treatment response.