BACKGROUND: ESR1 mutations are frequently detected in ER+ MBC, and have been reported to be associated with endocrine therapy resistance. However, there are little researches to validate whether dynamic monitoring of ESR1 mutations could serve as a predictive plasma biomarker of acquired resistance to endocrine therapy. Therefore, in this study, we performed longitudinal circulating tumor DNA (ctDNA) detection to evaluate the clinical implications of monitoring ESR1 mutations. METHODS: We performed longitudinal dynamic mutation analyses of plasma samples from 45 patients with metastatic breast cancer (MBC) and sequencing paired biopsy tissues, using a targeted NGS panel of 425 genes. These patients were treated at the Second Affiliated Hospital of Dalian Medical University between January 2017 and February 2019 with written informed consent. RESULTS: Mutations profiles were highly concordant between plasma and paired tissue samples from 45 MBC patients (r = 0.96, P < 0.0001). ESR1 mutations were enriched in ER+ MBC patients after AI therapy (17.8%, 8/45). The median time from AI endocrine therapies to the initial detection of ESR1 mutation was 39 months (95% CI 21.32–57.57). Some hotspot mutations (Y537S (n = 5), Y537N (n = 1), D538G (n = 2), E380Q (n = 2)) and several rare mutations (L345SfsX7, 24fs, G344delinsGC) were identified in our cohort. In addition, we observed that two patients obtained multiple ESR1 mutations over the course of treatment (Y537N/Y537S/D538G, L345SfsX7/24fs/E380Q). Through dynamically monitoring ESR1 mutations by ctDNA, we demonstrated that the change of allele frequency of ESR1 mutations was an important biomarker, which could predict endocrine resistance of ER+ MBC in our study. We also observed that the combination of everolimus in four cases with acquired ESR1 mutations showed longer PFS than other therapies without everolimus. CONCLUSION: The dynamic monitoring of ESR1 mutations by ctDNA is a promising tool to predict endocrine therapy resistance in ER+ MBC patients.

Approximately 30% of breast cancer (BC) patients suffer from disease relapse after definitive treatment. Monitoring BC at baseline and disease progression using comprehensive genomic profiling would facilitate the prediction of prognosis. We retrospectively studied 101 BC patients ultimately experiencing relapse and/or metastases. The baseline and circulating tumor DNA-monitoring cohorts included patients with baseline tumor tissue and serial plasma samples, respectively. Samples were analyzed with targeted next-generation sequencing of 425 cancer-relevant genes. Of 35 patients in the baseline cohort, patients with TP53 mutations (P < 0.01), or CTCF/ GNAS mutations (P < 0.01) displayed inferior disease-free survival, and patients harboring TP53 (P = 0.06) or NOTCH1 (P = 0.06) mutations showed relatively poor overall survival (OS), compared to patients with wild-type counterparts. Of the 59 patients with serial plasma samples, 11 patients who were newly detected with TP53 mutations had worse OS than patients whose TP53 mutational status remained negative (P < 0.01). These results indicate that an inferior prognosis of advanced breast cancer was potentially associated with baseline TP53, CTCF, and NOTCH1 alterations. Newly identified TP53 mutations after relapse and/or metastasis was another potential prognostic biomarker of poor prognosis.

BackgroundPhenylbutazone (PBZ) is the most commonly used drug to treat symptoms of lameness in horses; however, it is associated with adverse effects such as gastric ulcer syndrome (EGUS). Interestingly, many practitioners prescribe omeprazole (OME) concurrently with PBZ to prevent the development of EGUS. However, the efficacy and safety of this practice in Mongolian horses with chronic lameness remain unknown.ObjectivesTo evaluate the clinical effects of a combination of PBZ and OME on chronic lameness in Mongolian horses.Study designRandomised block experimental design.MethodsEighteen Mongolian horses with lameness score was ≥3 points, were divided into three treatment groups, with six horses in each group: placebo (CON), PBZ (4.4 mg/kg PO q. 24 h), or PBZ plus OME (4 mg/kg PO q. 24 h; PBZ + OME) in a randomised block design based on the initial lameness score. The horses were treated for 15 days. During this period, weekly gastroscopy, and physiological and biochemical tests were performed.ResultsBoth PBZ (median 1.0, interquartile range [IQR]: 0.8–1.3; p = 0.01) and PBZ + OME (median 1.0, IQR: 1.0–1.0; p = 0.01) significantly decreased the lameness score compared with before administration. In addition, PBZ significantly increased the equine glandular gastric disease (EGGD) score (3.0 ± 0.6, p < 0.001), GT‐17 content (293.4 ± 21.8 pg/mL, p < 0.001), and pepsinogen‐1 (PG1) content (295.3 ± 38.3 ng/mL, p < 0.001) compared with CON or PBZ + OME. However, it significantly reduced the total protein (53.6 ± 1.5 g/L, p < 0.05) and albumin (25.5 ± 1.8 g/L, p < 0.05) contents. Nevertheless, compared with PBZ, PBZ + OME significantly decreased the EGGD score (0.3 ± 0.5, p < 0.001) and significantly increased the gastric fluid pH (7.3 ± 0.5, p < 0.001), total protein content (62.5 ± 4.6 g/L, p = 0.009), and albumin content (29.4 ± 1.1 g/L, p = 0.004). Meanwhile, they significantly diminished the gastrin 17 (GT‐17) (162.0 ± 21.0 pg/mL, p < 0.001) and PG1 (182.4 ± 22.5 ng/mL, p < 0.001) contents.Main limitationsIndividual differences in horses were larger, but the sample size was small. There was larger interval between observations for each index.ConclusionsCompared with PBZ alone, PBZ + OME had no therapeutic effect on chronic lameness; however, it reduced the occurrence of EGGD in Mongolian horses. Horses may be protected against chronic lameness and PBZ‐induced EGGD by increasing the pH value, decreasing serum PG1 and GT‐17 content, and preventing the reduction of myeloperoxidase content.

e13039 Background: Palbociclib has been approved as the first CDK4/6 inhibitor in China since 2018. This study aimed to collect real-world data for retrospective analysis of the clinical outcomes and potential clinical and genetic risk factors for Palbociclib plus ET. Methods: Data of 194 HR+HER2- ABC patients who received Palbociclib plus ET between May 2018 and Dec 2020 were collected from the electronic medical record system of seven cancer centers across China. Cox regression models and bioinformatic analysis were conducted to investigate the risk factors. Results: In total, 194 patients were included in the study. Among them, 138 patients discontinued Palbociclib plus ET due to disease progression (130 patients), financial inability (5 patients), or intolerable adverse reactions (3 patients) as of the observation endpoint. With a median follow-up period of 22.4 months, the median progression-free survival (mPFS) was 12.3 months, the median time to failure (mTTF) was 11.8 months, and the median overall survival (mOS) was 35.5 months. Moreover, the 1-year PFS, TTF and OS rates were 50.8%, 49.0% and 87.6%, respectively. Of the 155 with measurable disease, the objective response rate (ORR) was 27.1%, the disease control rate (DCR) was 71.6% and the clinical benefit rate (CBR) was 81.3%. KM curves showed that first-line users had the mPFS of 19.0 months, which was significantly longer than the second-line users and the third (or higher) line users (mPFS = 10.7 and 7.2 months, p＜0.0001). Multivariate Cox regression analysis revealed several clinical features as risk factors, whereas liver metastasis was a significant risk factor for poor PFS and OS (HR = 1.993, [95%CI, 1.243-3.195], p = 0.004; HR = 2.345, [95%CI, 1.089-5.049, p = 0.029). Central nervous system (CNS) metastasis was an independent risk factor for poor OS (HR = 2.658, [95%CI, 1.152-6.136], p = 0.022). Response to CR/PR was a significant protective factor for PFS (HR = 0.289, [95%CI, 1.161-0.519], p＜0.001) but not for OS. Postmenopausal patients had a higher PFS risk than premenopausal patients (HR = 1.549, [95%CI, 1.007-2.382], p = 0.046). Seven patients received circulating tumor DNA (ctDNA) testing at the baseline and after disease progression, which showed that the mutation frequencies of FGFR1, ARID1A, ATRX, CHD4, FAT1, and PTEN increased significantly after disease progression. Conclusions: Treatment with Palbociclib plus ET exhibited favorable efficacy for HR+HER2– ABC in Chinese real-world practices, especially for non-liver, non-CNS metastasis or premenopausal patients. Early-line treatment yielded more durable benefits, and response to CR/PR indicated a better PFS prognosis. Mutations in FGFR1, ARID1A, ATRX, CHD4, FAT1, and PTEN might be associated with resistance to the combination therapy.

e13048 Background: Randomized controlled trials (RCTs) found that PAL plus ET had a considerable survival advantage in patients with HR+/HER2- ABC compared to ET. This real-world study aimed to complement the existing RCTs in addition to accounting for patient characteristics, adherence to treatment, and socioeconomic factors. Methods: Data of patients who had HR+HER2- ABC and received PAL plus ET (N=216) and ET (N=215) from September 2007 to May 2020 were retrospectively retrieved from the electronic medical record system of seven cancer centers across China. Stabilized inverse probability of treatment weighting (SIPTW) was applied to strictly balance the variables between the two cohorts. Results: A total of 400 patients were eligible for the study analysis. PAL plus ET was administered to 204 (51%) patients, and 196 (49%) patients received ET only. At the end of the observation, treatment failure occurred in 162 (79%) patients and 183 (93%) patients in both cohorts, due to disease progression (93.2% vs. 96.8%), financial inability (4.9% vs. 0%), intolerable adverse reactions (1.9% vs. 0.5%), and unknown reasons (0% vs. 2.7%). Most patients were postmenopausal (71.8%) and had visceral metastasis (65.2%). De-novo metastatic disease was seen in 13.0% of patients, and 45.2% of patients received first-line ET. More than half of the patients (57.8%) received aromatase inhibitors, and 38.5% received estrogen receptor degrader fulvestrant. With a median follow-up period of 39.5 and 40.5 months, the median TTF in PAL plus ET vs. ET was 11.8 vs. 9.47 months (HR=0.69, 95% CI: 0.56-0.86, p=0.00057), and OS analysis showed a median OS not reached (NR) vs. 40.7 months (HR=0.84, 95% CI: 0.62-1.13, p=0.25). Upon SIPTW, the standardized differences (-0.117 to 0.096) showed a good balance between the cohorts. Weighted median TTF was significantly longer in the PAL plus ET group than the ET group (11.8 vs. 7.07 months, HR=0.63, 95% CI: 0.49-0.80, p=0.000139). However, the results of weighted median OS were not statistically significant (NR vs. 38 months, HR=0.80, 95% CI: 0.53-1.21, p=0.29). In the balanced subgroup analysis, TTF showed a similar trend to that in the overall population, and in patients with de-novo metastatic disease and non-central nervous system (CNS) metastasis, OS was significantly longer in the PAL plus ET group than ET (HR=0.256, 95% CI: 0.112-0.586, p for interaction=0.013; HR=0.657, 95% CI: 0.443-0.973, p for interaction=0.013, respectively). Conclusions: Comparatively, PAL plus ET had significantly longer TTF than ET, supporting the use of PAL plus ET in HR+/HER2– ABC patients in real-world settings. In patients with de-novo metastatic disease and non-CNS metastasis, PAL plus ET showed significant OS benefit compared to ET, however, follow-up time needs to be increased in further studies.