For unresectable advanced gastric malignancies causing malignant gastric outlet obstruction(GOO) and malignant biliary obstruction(MBO), traditional treatment methods include surgical gastrojejunostomy and hepatojejunostomy. However, surgical treatment is associated with many complications and prolonged recovery. We report a case of a 56-year-old male patient who complained of nausea and vomiting after meals for one month. Esophagogastroduodenoscopy(EGD) revealed a malignant gastric tumor, pyloric obstruction, and gastric retention. Abdominal CT revealed multiple liver metastases and distant lymph nodes metastases. Two duodenal stents were placed within two months to relieve the malignant GOO. Five months later, rapid tumor progression led torecurrent malignant GOO and involvement of the duodenum, resulting in MBO. Since endoscopic retrograde cholangiopancreatography(ERCP) was not feasible, we relieved the MBO through endoscopic ultrasound guided antegrade stenting (EUS-AS). One week later, GOO was treated with endoscopic ultrasound guided gastroenterostomy (EUS-GE). During the 6-month follow-up period, the patient experienced no recurrence of obstructive jaundice or gastric retention, and the treatment was effective. Endoscopic stent placement can relieve malignant double obstruction,with minimal complications and rapid recovery. Endoscopic interventions are repeatable and provide immediate and reliable clinical benefit.

Background:Existing neoadjuvant therapies for hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+/HER2-) breast cancer have not achieved optimal clinical outcomes, thus prompting the investigation of novel treatment strategies. Given the emerging significance of HDAC inhibitors in the management of advanced breast cancer, this study investigated the efficacy and safety of chidamide plus chemotherapy as neoadjuvant therapy for patients with HR+/HER2- breast cancer. Methods:This single arm, open-label, multicentre, phase 2 trial was conducted at three hospitals in China. Patients aged 18-75 years who had treatment-naïve, stage II-III HR+/HER2- breast cancer with an Eastern Cooperative Oncology Group performance status of 0-1 were enrolled. Patients received oral chidamide at a dose of 20 mg on days 1, 4, 8, and 11 of each 21-day cycle. The chemotherapy regimen consisted of four cycles of epirubicin (90 mg/m2) and cyclophosphamide (600 mg/m2) administered every three weeks, followed by four cycles of docetaxel (100 mg/m2) administered every three weeks. The primary endpoint was the rate of residual cancer burden (RCB) 0-I. This study is registered with ClinicalTrials.gov, NCT05400993. Findings:Between May 23, 2022 and July 6, 2023, a total of 54 female patients (median age: 50 years [range, 26-75]) were recruited. The RCB 0-I rate was 35.2% (19 of 54, 95% confidence interval [CI], 22.7%-49.4%). The most frequent grade 3 or 4 adverse events were decreased neutrophil count (70%) and decreased white blood cell (67%). No treatment-related deaths occurred. Interpretation:The combination of chidamide and chemotherapy shows the potential to be an alternative neoadjuvant therapy option for patients with HR+/HER2- breast cancer. Funding:Shenyang Municipal Science and Technology Program (Grant No. 22-321-32-18), Shenzhen Chipscreen Biosciences Co., Ltd.

Antibody-drug conjugates (ADCs) and tyrosine kinase inhibitors (TKIs) are widely used for HER2-positive metastatic breast cancer, but their efficacy in the neoadjuvant setting remains under investigation. The MUKDEN 06 trial (NCT05426486), a multicentre, randomised, phase 2b study, compared ARX788 (anti-HER2 ADC) plus pyrotinib (TKI) with the standard neoadjuvant regimen of docetaxel, carboplatin, trastuzumab, and pertuzumab (TCbHP) in female patients with early or locally advanced HER2-positive breast cancer. The primary endpoint was the pathological complete response (pCR, ypT0/is, ypN0) rate, analyzed in the intention-to-treat population. pCR was achieved in 70.6% (48/68) of patients receiving ARX788 plus pyrotinib, compared to 51.5% (35/68) in the TCbHP group, with a significant absolute difference of 19.1% (95% CI, 2.7-34.6; p = 0.023). No treatment-related deaths occurred. The most common grade 3-4 adverse events were diarrhea and hepatic dysfunction in the ARX788 plus pyrotinib group, and fatigue, nausea and anorexia in the TCbHP group. Interstitial lung disease (ILD)/pneumonitis and ocular events were observed with ARX788 plus pyrotinib, indicating a distinct safety profile. These findings offer clinical insights into the potential of dual HER2-targeted blockade with an ADC and TKI as an optional neoadjuvant strategy for patients with early or locally advanced HER2-positive breast cancer.

Enhancing the precision of computer-assisted polyp segmentation and delineation during colonoscopies assists in the removal of potentially precancerous tissue, thus reducing the risk of malignant transformation. Most of the current medical segmentation models use the traditional U-shaped network structure, but they suffer from the problem of information loss during the encoding and decoding of images. To advance towards an autonomous model for detailed polyp segmentation, the authors propose a new framework for polyp segmentation called U-shaped cross-fusion network with attention mechanism (UCFA-Net), which employs a pyramid vision transformer as encoder to extract image features at multiple scales. Furthermore, the multi-scale cross-fusion module cross-fuses the different scale features and then goes through the multi-scale convolutional parallel feedforward transformer module for modelling the global and local information. Finally, progressive attentional up-sampling module acts as a decoder for up-sampling with progressive attention to get the final polyp segmentation result. The authors comprehensive testing demonstrates that their network achieves superior average scores across the five datasets and exhibits greater robustness in the face of diverse and demanding scenarios, when compared to current state-of-the-art approaches.

Study objectivePhyllodes tumors of the breast (PT) are rare fibroepithelial tumors with varied clinical and histopathological characteristics, and standardized with wide margins in surgery, a systemic retrospective study of PT could improve our understanding of prognosis.DesignWe conducted a retrospective study spanning 2008-2021, which included 333 cases of PT for chart review. We used logistic regression and comparison tests to evaluate the association between clinical features and local recurrence (LR), as well as to summarize overall survival (OS) and disease-free survival (DFS).SettingPhyllodes tumors of the breast exhibit a propensity for a higher recurrence rate. The surgical protocol advocates for achieving wide margins (>1 cm), which presents challenges in clinical practice due to the ambiguity in defining such margins.ParticipantsA retrospective screening identified 333 cases of PT for inclusion in the study. Comprehensive data for this analysis was extracted from the clinical patient records.InterventionsPost-operation, all cases were subjected to a standardized protocol of regular follow-up , with subsequent documentation of follow-up data.Main outcome measuresAt a median follow-up of 79 (inter-quartile range: 28-109) months, recurrence occurred in 9.7% (19/196) of benign, 18.4% (18/98) of borderline, and 28.2% (11/39) of malignant tumors. Local recurrence was not reduced with enlarged margin width (<1 cm vs. >1 cm: odds ratio (OR)=0.84; 95% CI, 0.48 to 1.47; p=0.53), but it was associated with age (<40 vs. >40: OR=2.04; 95% CI, 1.13 to 3.68; p=0.01). LR was significantly correlated with mitosis (<5/HFP vs. >=5/HFP: OR=0.56; 95% CI, 0.32 to 0.98; p=0.003), stromal overgrowth (yes vs. no: OR=0.43; 95% CI, 0.32 to 0.98; p=0.014), and stromal atypia (mild vs. marked: OR=0.59; 95% CI, 0.30 to 1.17; p=0.003).Result and conclusionThis retrospective study confirmed that recurrence and prognosis were not associated with wide margins in the real world, as suggested by previous guidelines, possibly due to the influence of characteristics such as age, stromal overgrowth, stromal atypia, and mitosis.

Giant breast malignant phyllodes tumor or sarcoma (GBPS) are rare entities with diameter larger than 10 cm and variously histological pleomorphisms. This disease poses a significant threat to the quality of life of individuals, and its prognosis remains unclear. This study aimed to explore the differential diagnosis, treatment, and prognosis of GBPS in a real-world retrospective cohort. We collected GBPS (diameter > 10 cm, n = 10) and BPS (diameter ≤ 10 cm, n = 126) from patients diagnosed with sarcoma or malignant phyllodes tumor between 2008 and 2022. We analyzed clinical characteristics, histological status, treatment, and local recurrence using the Fisher’s exact test between GBPS (diameter > 10 cm) and BPS (diameter ≤ 10 cm) cohort. We described overall survival (OS) and disease-free survival (DFS) using Kaplan–Meier curves and identified risk factors for local recurrence using logistic regression. The tumor size, age at diagnosis, and differential immunohistochemistry markers of breast sarcoma or phyllodes tumor to determine the prognosis of GBPS. In our retrospective analysis of breast malignancies, we identified 10 cases of GBPS and 126 cases of BPS, corresponding to a GBPS prevalence of 0.17

Background: Emerging data have supported the immunostimulatory role of radiotherapy, which could exert a synergistic effect with immune checkpoint inhibitors (ICIs). With proven effective but suboptimal effect of ICI and chemotherapy in triple-negative breast cancer (TNBC), we designed a pilot study to explore the efficacy and safety of neoadjuvant stereotactic body radiotherapy (SBRT) plus adebrelimab and chemotherapy in TNBC patients. Methods: Treatment-naïve TNBC patients received two cycles of intravenous adebrelimab (20 mg/kg, every 3 weeks), and SBRT (24 Gy/3 f, every other day) started at the second cycle, then followed by six cycles of adebrelimab plus nab-paclitaxel (125 mg/m² on days 1 and 8) and carboplatin (area under the curve 6 mg/mL per min on day 1) every 3 weeks. The surgery was performed within 3–5 weeks after the end of neoadjuvant therapy. Primary endpoint was pathological complete response (pCR, ypT0/is ypN0). Secondary endpoints included objective response rate (ORR), residual cancer burden (RCB) 0-I, and safety. Results: 13 patients were enrolled and received at least one dose of therapy. 10 (76.9%) patients completed SBRT and were included in efficacy analysis. 90% (9/10) of patients achieved pCR, both RCB 0-I and ORR reached 100% with three patients achieved complete remission. Adverse events (AEs) of all-grade and grade 3–4 occurred in 92.3% and 53.8%, respectively. One (7.7%) patient had treatment-related serious AEs. No radiation-related dermatitis or death occurred. Conclusions: Adding SBRT to adebrelimab and neoadjuvant chemotherapy led to a substantial proportion of pCR with acceptable toxicities, supporting further exploration of this combination in TNBC patients. Funding: None. Clinical trial number: NCT05132790.

e12617 Background: Both neoadjuvant chemotherapy and endocrine therapy only result in trivial pathological complete response rates and moderate objective response rate (ORR) in hormone receptor (HR)-positive, HER2-negative breast cancer, more promising alternatives are urgently needed. Tucidinostat is an oral subtype-selective histone deacetylase inhibitor that has shown efficacy and safety when used in combination with exemestane in patients with advanced HR+ breast cancer. This MUKDEN 05 study aimed to assess the efficacy and toxicity of the combination of tucidinostat and EC-T as a neoadjuvant strategy in patients with HR+/HER2-, stage II-III breast cancer. Methods: This study is a multicenter, single-arm, phase II study. Eligible patients received 20 mg tucidinostat orally twice a week (on days 1, 4, 8, and 11), 2 weeks on, 1 week off. The dose and administration schedule of EC-T were as follows: 4 cycles of epirubicin 90 mg/m2 and cyclophosphamide 600 mg/m2 every 3 weeks, followed by 4 cycles of docetaxel 100 mg/m2 every 3 weeks. The primary endpoint was the proportion of residual cancer burden (RCB) 0-I. Key secondary endpoints included pathological complete response (pCR), objective response rate (ORR), and safety. Results: Between May 2022 and August 2022, a total of 35 patients were enrolled. 27 patients were pathologically evaluable. The remaining 8 patients have completed neoadjuvant treatment and wait for operation. The ratio of RCB 0-I was 37% (95% CI, 23.2-53.7%). ORR was 86% (95% CI, 70.6-93.7%). Four (15%; 95% CI, 5.91-32.5%) patients achieved bpCR, and one (4%; 95% CI, 0.67-18.3%) patients achieved tpCR. Most adverse events (AEs) were grade 1 or 2. Grade 3/4 AEs included neutropenia (21.1%), and thrombocytopenia (15.8%). Conclusions: The combination of Tucidinostat and EC-T had an acceptable safety profile and encouraging clinical responses, offering a neoadjuvant treatment option for patients with early HR+/HER2- breast cancer. Further research is required to validate these findings. Clinical trial information: NCT05400993 .

HNF4α, a transcription factor, plays a vital role in regulating functional genes and biological processes. Its alternative splicing leads to various transcript variants encoding different isoforms. The spotlight has shifted towards the extensive discussion on tumors interplayed withHNF4α abnormalities. Aberrant HNF4α expression has emerged as sentinel markers of epigenetic shifts, casting reverberations upon downstream target genes and intricate signaling pathways, most notably with cancer. This review provides a comprehensive overview of HNF4α's involvement in tumor progression and metastasis, elucidating its role and underlying mechanisms.

Objective: Studying the prognosis of breast cancer (BRCA) is of great significance for clinical treatment. LncRNA has been shown to be significantly important in breast cancer, but only few studies exist that relate to the prognosis of lncRNA. This study aimed to build a lncRNA-based breast cancer prognosis risk model using the data from TCGA datasets. Methods: we used the TCGA public database to explore the differential expression of lncRNA and cancer prognosis in breast cancer patients. The RNA-Seq data and clinical data pertaining to 1090 BRCA patients in the TCGA database were downloaded and analyzed. The prognosis-related lncRNAs in BRCA patients were identified in the training set and validated in the test set and the complete data set. ROC was performed to determine the optimal cut-off point for patient risk classification, and survival analysis was performed to determine its significance in prognosis prediction. Results: A total of 19 prognosis-associated differentially expressed lncRNAs (LSINCT5, TRG-AS1, CH17-189H20.1, RP11-1399P15.1, RP11-344P13.6, RP5-1028K7.2, AL022344.7, USP30-AS1, RP11-522120.3, AL122127.25, BHLHE40-AS1, CHRM3-AS2, LINC00704, RP5-107303.2, RP11-316M21.6, CTA-384D8.31, RP11-10J5.1, RP11-426L16.3, RB11-344B5.2) were screened out. The BRCA prognosis risk assessment model based on 19-lncRNA can predict the survival rate of breast cancer patients. Conclusion: This model can predict the prognosis of breast cancer patients and these 19 lncRNAs can be used as potential molecular markers for breast cancer prognosis prediction.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The cyclin-dependent kinase 2 (CDK2) inhibitor dinaciclib, a potential anti-cancer drug, has been tested in clinical trials and reported to suppress tumor initiating cells. Our recent study demonstrated that pharmacological inhibition of CDK2 or enhancer of zeste homolog 2 (EZH2) allows re-expression of ERα and converts triple-negative breast cancers (TNBC) to luminal ERα-positive, rendering TNBC cells targetable by tamoxifen. Like TNBC, EZH2 is also commonly overexpressed in ovarian cancers, and overexpression of cyclin E1 gene (CCNE1) and/or amplification of its associated kinase CDK2 gene is present in ovarian tumor specimens, both of which are associated with primary treatment resistance and poor outcome in high-grade serous ovarian cancer (HGSC). We determined whether inhibition of CDK2-mediated phosphorylation of EZH2 activates ERα expression in ERα-negative HGSOC cells, rendering them targetable by hormonal therapy. The specific CDK2 inhibitor repressed phosphorylation of EZH2 at T416, and in turn activated the expression of its downstream target ERα gene (ESR1). We tested the efficacy of the combination of CDK2 inhibitor and tamoxifen and found significant synergistic inhibition. We further demonstrated that CDK2 inhibitor is a more promising agent than EZH2 inhibitor in repressing TNBC and HGSOC due to a feedback increase in CDK2 activity by EZH2 inhibitor. Our results indicated that the combination treatment of CDK2 inhibitor and tamoxifen has the potential to benefit patients with ERα-negative HGSOC.

The limited treatment options and therapeutic failure due to acquired resistance for patients with triple-negative breast cancer (TNBC) represent a significant challenge. Inhibitors against poly (ADP-ribose) polymerase (PARP), olaparib and talazoparib, were recently approved for the treatment of metastatic breast cancer (including TNBC) in patients with germline BRCA1/2 mutations. Despite impressive response rates of ~60%, the prolongation in median progression-free survival with a PARPi is modest, suggesting the emergence of resistance. Several studies have reported that receptor tyrosine kinases (RTKs), such as c-MET (also known as hepatocyte growth factor receptor), are involved in resistance to various anti-neoplastic agents, including PARPi. However, the mechanism by which c-MET contributes to acquired resistance to PARPi in TNBC is not fully understood. In this study, we show that hyperactivated c-Met is detected in TNBC cells with acquired resistance to PARPi, and the combination of talazoparib and crizotinib (a multi-kinase inhibitor that inhibits c-MET) synergistically inhibits proliferation in these cells. Unexpectedly, depleting c-MET had limited effect on talazoparib sensitivity in PARPi-resistant cells. Interestingly, we found evidence of epidermal growth factor receptor (EGFR) hyperactivation and interaction of EGFR/c-Met in these cells. Notably, combining EGFR and PARP inhibitors resulted in greater inhibition of proliferation in c-MET-depleted TNBC cells, and combined c-MET and EGFR inhibition increased sensitivity to talazoparib in TNBC cells with acquired resistance to PARPi. Our findings suggest that combined inhibition of c-MET and EGFR could potentially re-sensitize TNBC to the cytotoxic effects of PARPi.

BACKGROUND We analyzed the clinical and imaging characteristics of patients with breast ductal carcinoma in situ with microinvasion (DCISM) and breast ductal carcinoma in situ (DCIS). METHODS We analyzed the records of 40 patients diagnosed with DCISM and 61 patients with DCIS who were hospitalized at Shengjing Hospital (Shenyang, China) from January 2009 to June 2016. The size, hardness, and degree of calcification of tumors were determined by mammography and ultrasonography. RESULTS In all, 37 DCISM patients and 45 DCIS patients showed clinical palpable masses (92.5% vs 73.77%, P = 0.018). Mammography showed that the mean size of tumor was larger in DCISM patients than that of DCIS patients (3.13 ± 1.51 vs 2.68 ± 1.77, P = 0.030). Ultrasound examination revealed calcification shadows in the solid tumor mass in 17 DCISM cases and 11 DCIS patients (42.5 vs 18.03%, P = 0.007). Furthermore, estrogen receptor positivity and progesterone receptor positivity were more common in DCIS patients (32.5% vs 54.10%, P = 0.033; 22.5% vs 45.90%, P = 0.017), and the percentage of menopausal patients were higher in DCISM patients than that of DCIS patients (70.00% vs 47.54%, P = 0.026). CONCLUSION Clinically palpable and calcified tumor masses on sonography are more commonly encountered in DCISM lesions.

Poly (ADP-ribose) polymerase (PARP) inhibitors are a therapeutic milestone exerting a synthetic lethal effect in the treatment of cancer involving BRCA1/2 mutation. Theoretically, PARP inhibitors (PARPi) eliminate tumor cells by disrupting DNA damage repair through either PARylation or the homologous recombination (HR) pathway. However, resistance to PARPi greatly hinders therapeutic effectiveness in triple-negative breast cancer (TNBC). Owing to the high heterogeneity and few genetic targets in TNBC, there has been limited therapeutic progress in the past decades. In view of this, there is a need to circumvent resistance to PARPi and develop potential treatment strategies for TNBC. We present, herein, a review of the scientific progress and explore the mechanisms underlying PARPi resistance in TNBC. The complicated mechanisms of PARPi resistance, including drug exporter formation, loss of poly (ADP-ribose) glycohydrolase (PARG), HR reactivation, and restoration of replication fork stability, are discussed in detail in this review. Additionally, we also discuss new combination therapies with PARPi that can improve the clinical response in TNBC. The new perspectives for PARPi bring novel challenges and opportunities to overcome PARPi resistance in breast cancer.

Leveraging compromised DNA damage repair (DDR) pathways commonly found in tumor cells, a classic strategy in cancer therapy is inducing excessive DNA damage to cause cancer cell death. Small molecule poly(ADP-ribose) polymerase (PARP) inhibitors (PARP-is) have been approved for clinical use in treating breast cancer and ovarian cancer patients bearing DDR-deficient tumors with mutations in breast cancer susceptibility proteins (BRCAm). However, accumulating evidences show that both intrinsic and acquired resistances to PARP-is exist in clinic and pre-clinical animal models. Therefore, we developed panels of cells with acquired PARP-is resistance from PARP-is-sensitive triple negative breast cancer (TNBC) and estrogen receptor positive breast cancer cell lines, and used these cells to screen for common traits that can be targeted with feasible therapeutic agent combinations to overcome PARP-is resistance. Since TNBC lacks of effective targeted therapy so far, we focused on using the panel of PARP-is-resistant TNBC cells in this study. Among the molecular mechanisms known contribute to PARP-is resistance, oncogenic kinase activations, including several hyper-activated receptor tyrosine kinases (RTKs), are involved in enhancing DNA damage repair and decreasing affinity of PARP-is to PARP1. In this study, we systematically screened for activated RTKs in the PARP-is-resistant cells we developed by antibody arrays. We then identified that activations of MET, Axl and EphA2 were common traits in TNBC cells with acquired PARP-is resistance, but not in estrogen receptor positive cells. Among the three RTKs, MET has more small molecules inhibitors that can target it, and thus, we made it a priority in investigating synergism between MET inhibitor and PARP inhibitor in multiple cancer types including TNBC with intrinsic and acquired PARP-is-resistance, high-grade serous ovarian cancer (HGSOC) and liver cancer cells. Here, we demonstrated that combinations of PARP-is and MET inhibitors (MET-is) possess moderate to strong synergism in the different cancer types we studied. As we previously reported that MET translocates into cell nucleus and phosphorylates PARP1 at tyrosine (Y) 907 residue in TNBC with intrinsic PARP-is resistance, we found that this MET-mediated PARP1-Y907 phosphorylation also exist in and can serve as marker to indicate PARP-is resistance among the HGSOC, liver cancer cells and the TNBC cells with acquired PARP-is resistance. We further found that MET phosphorylation is high (immunohistological staining H-score greater than 200) in breast cancer (23 out of 31, 70%) and ovarian cancer (8 out of 23, 35%) patient-derived xenograft mouse model tissue microarrays, suggesting that the combination of MET-is and PARP-is is likely to benefit a huge population of cancer patient in multiple cancer types. Citation Format: Mei-Kuang Chen, Weiya Xia, Qiongzhu Dong, Yi Du, Hung-Ling Wang, Coya Tapia, Yongkun Wei, Ye Han, Yu-Yi Chu, Clinton Yam, Yuan Gao, Yu-Han Wang, Funda Meric-Bernstam, Jinsong Liu, Shao-Chun Wang, Dihua Yu, Mien-Chie Hung. Synergism of PARP inhibitor and MET inhibitor in multiple cancer types with intrinsic and acquired PARP inhibitor resistances [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5682.

Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) are promising targeted therapeutics for breast and ovarian cancers bearing a germline BRCA1/2 mutation (BRCAm), and several have already received regulatory approval in the United States. In patients with a BRCAm cancer, PARPi can increase the burden of unrepaired DNA double-strand breaks by blocking PARP activity and trapping PARP1 onto damaged DNA. Resistance to PARP inhibitors can block the formation of DNA double-strand breaks through BRCA-related DNA repair pathway. MET is a hyper-activated receptor tyrosine kinase expressed in multiple cancer types and the activation contributes to resistance to DNA damage-inducing therapeutic drugs. Our previous study showed that MET inhibition by pan-kinase inhibitors has synergism with PARPi in suppressing growth of breast cancer in vitro and in xenograft tumor models. In this study, we validated the inhibitory effect of novel inhibitors, HS10241 (selective MET inhibitor) and HS10160 (PARPi), to their target respectively in triple-negative breast cancer (TNBC) and high-grade serous ovarian cancer (HGSOC) cells. We further demonstrated that these two inhibitors function synergistically in eliminating TNBC and HGSOC cells; combining with HS10241 increased DNA double-strand breaks induced by HS10160 in cancer cells; and PARP1 tyrosine (Y)-907 phosphorylation (PARP1 p-Y907) can be an effective biomarker as an indicator of MET-mediated PARPi in HGSOC. Our results suggest that the combination of HS10241 and HS10160 may benefit patients bearing tumors overexpressing MET as well as those resistant to single-agent PARPi treatment.

1063 Background: Poly (ADP-ribose) polymerase (PARP) inhibitors have emerged as promising targeted therapies for BRCA-mutated cancers by blocking repair of DNA double-strand breaks. However, resistance to PARP inhibitors have been described in some patients lowering overall response rates. The mechanisms underlying PARP inhibitor (PARPi) resistance are an area of active investigation. Methods: PARPi adaptive resistant clones (MDA-MB-468, MDA-MB-231, HCC1806) were generated in triple-negative breast cancer cell lines. Through morphologic observation and functional analysis, we evaluated epithelial-mesenchymal transition (EMT) and changes in immune checkpoint programmed death-ligand 1 (PD-L1). We also downregulated the expression of PD-L1 by shRNA to study the role of PD-L1 in PARPi resistance. We evaluated the immunology sensitivity to cytotoxic T cell upon PD-L1 change using a murine ex-vivo CD8+ T cell killing assay and a comparison of total killing cells percentage per well. Results: We demonstrated that inhibition of PARP enhances EMT, which induces phosphorylation of Akt at S473. This in turn upregulates the expression of PD-L1 by 2-3 fold in triple-negative breast cancer cells. In addition, PARPi–induced EMT occurred independent of PD-L1 upregulation in triple-negative breast cancer cells. Metformin administration (10µM) was found to reverse EMT by blocking the p-Akt S473 axis through activation of AMPK, resulting in downregulation of PD-L1 expression and sensitizing PARPi-resistant cancer cells to T cell killing. Conclusions: In summary, we identified that induction of EMT is a new mechanism for PARP inhibitor resistance. Metformin was able to reverse EMT and therefore a combination of metformin and PARP inhibitors may be a promising therapeutic strategy to increase the efficacy of PARP inhibitors and tumor sensitivity to T cells.

Triple-negative breast cancer (TNBC), which lacks estrogen receptor α (ERα), progesterone receptor, and human epidermal growth factor receptor 2 (HER2) expression, is closely related to basal-like breast cancer. Previously, we and others report that cyclin E/cyclin-dependent kinase 2 (CDK2) phosphorylates enhancer of zeste homolog 2 (EZH2) at T416 (pT416-EZH2). Here, we show that transgenic expression of phospho-mimicking EZH2 mutant EZH2T416D in mammary glands leads to tumors with TNBC phenotype. Coexpression of EZH2T416D in mammary epithelia of HER2/Neu transgenic mice reprograms HER2-driven luminal tumors into basal-like tumors. Pharmacological inhibition of CDK2 or EZH2 allows re-expression of ERα and converts TNBC to luminal ERα-positive, rendering TNBC cells targetable by tamoxifen. Furthermore, the combination of either CDK2 or EZH2 inhibitor with tamoxifen effectively suppresses tumor growth and markedly improves the survival of the mice bearing TNBC tumors, suggesting that the mechanism-based combination therapy may be an alternative approach to treat TNBC.