A phase II study of buparlisib in relapsed or refractory thymomas

PURPOSE

To investigate the efficacy and safety of buparlisib, an oral pan-PI3K inhibitor, in relapsed or refractory thymomas.

METHODS

This was a single center, single arm, open label phase II trial of buparlisib in patients with recurrent thymoma who have progressed after at least one prior line of treatment. The primary endpoint was objective response rate (complete response [CR] + partial response [PR]). Secondary endpoints included toxicity; progression free survival (PFS); overall survival (OS); disease control rate (DCR), i.e., the percentage of patients who achieve either PR or CR or stable disease [SD] for at least 4 months.

RESULTS

Between 10/13/2014 and 1/18/2017, 14 patients with stage IV disease were enrolled. Median age was 58y (23-74). 71% were females and 71% white. All patients had WHO B2 (29%) or B3 (71%) thymoma. Patients received buparlisib for a median of 4.5m (2-33). At a median follow up of 16.6m (2.4-31.3), onr patients (7%) achieved a PR. DCR was 50%. Median PFS was 11.1m (95% CI 2.9 - 18.8). Median OS, updated as of March, 2021 was 22.5m (10.7-31.3). Most common grade 3-4 adverse events related to buparlisib were dyspnea (21%), rash (14%), elevated transaminases (14%), cough (7%), pneumonitis (7%), anxiety (7%), fatigue (7%) and hyperglycemia (7%). Reasons for treatment discontinuation included progression of disease (n= 5), rash (n=4), pulmonary toxicity (n=3), sinusitis (n=1), and disseminated toxoplasmosis plus autoimmune cholangitis (n=1). As of 3/2021, 8 patients have died, 7 due to disease progression and 1 due to central nervous system toxoplasmosis and autoimmune cholangitis.

CONCLUSION

Buparlisib showed modest activity in patients with relapsed or refractory thymomas. Further investigation of PI3K pathway targeted therapy in thymoma is warranted. (clinicaltrials.gov ID: NCT02220855).

CLINICAL TRIAL REGISTRATION

clinicaltrials.gov, identifier (NCT02220855).

Abstract 1354: 4-marker positive selection system for improved CTC analysis in metastatic triple-negative breast cancer

Introduction: Circulating tumor cells (CTCs) represent a potent opportunity to glean important information about in vivo breast cancer biology using a non-invasive technique. However, EpCAM-based techniques are significantly limited by the presence of marker-negative CTCs, a phenotype that is enriched in the CTCs of metastatic triple-negative breast cancers (mTNBCs). This interim analysis is part of an exploratory study to investigate the utility of supplementing EpCAM with additional markers specifically relevant to mTNBC for more complete CTC enumeration.

Methods: Marker candidates used in this analysis were: (1) previously associated with TNBC, (2) exclusively surface markers to avoid permeabilization, (3) not associated with leukocytes or endothelial cells, and (4) targetable with commercially available antibodies. TNBC cell lines were characterized across the selected markers by flow cytometry. Immunomagnetic enrichment (IE) of cell lines from culture medium was conducted using antibodies conjugated to magnetic beads in concert with a rare cell detection system developed by the Savran Research Group at Purdue University. The recruitment goals for the study stand at twenty healthy individuals and twenty individuals with mTNBC. All blood samples were collected in CellSave tubes and were assessed using four-marker IE with a parallel monochromatic cross-stain. Anti-CD45 and Hoechst stain were incorporated into the cross-stain in standard fashion. Samples from individuals with mTNBC were also subjected to standard EpCAM-based CTC detection on the same device, which served as a pairwise baseline comparator.

Results: Surface expression of four markers, including TROP2, N-Cadherin, EGFR, and EpCAM, was assessed across eleven TNBC cell lines. All cell lines were positive for at least one of four markers in the panel. EpCAM-negative cell lines (4/11) were positive for N-Cadherin and/or EGFR. Unique to these cell lines, four-marker IE was significantly more efficient than EpCAM alone (p=0.0006). As of November 2018, ten normal and six mTNBC participants have been recruited. All blood samples were able to be analyzed. Healthy participants yielded 0 CTCs, with the exception of one participant, in which a single positive cell was found. CTCs were detected in 50% and 33% of participants with mTNBC when utilizing the experimental method vs. EpCAM-directed detection. Futher, in 100% (3/3) of cases in which CTCs were detected, the four-marker system detected more CTCs than the EpCAM-based comparator.

Discussion: Compared to EpCAM-based capture, the four-marker experimental system presented here has potential to enhance CTC analysis by more completely representing the heterogeneity of TNBC. This results in better overall capture efficiency and enumeration while still maintaining sufficient specificity. The parent analysis is expected to be completed in the summer of 2019.

Citation Format: Bradley Hancock, Chun-Li Chang, Yuan Zhong, Yu-Hsiang Chen, Jeffrey Solzak, Casey Bales, Emily Nelson, Robin Paul, Cagri Savran, Milan Radovich. 4-marker positive selection system for improved CTC analysis in metastatic triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1354.

Abstract P1-10-03: Precision therapeutic combinations are synergistic against triple negative breast cancer using compensatory pathways

Introduction: Triple negative breast cancer (TNBC) accounts for 15% of all breast cancer cases in the United States, and despite its lower incidence, contributes to a disproportionately higher rate of morbidity and mortality compared to other breast cancer subtypes. In an effort to treat TNBC, a cancer that has no targeted therapies, many have chosen to experiment with combinations of drugs that are chosen for their genomic expression or “hard targets”. It has been previously noted however, that single agent therapeutics can change the genomic landscape of both mice and human cells and may be responsible for resistance. Here we show that targeting a compensatory pathway after treatment with a single therapy, results in synergistic combinations and can outperform the choice of hard target therapies.

Methods: Eight TNBC cell lines were chosen based on their abundance of clinically actionable targets. The primary hard target combinations were chosen using data from TCGA and a board consisting of oncologists and researchers at Indiana University School of Medicine. Compensatory therapies were found using RNA sequencing data from untreated versus single therapeutic treated TNBC cell lines. The merged transcript RPKMs were transformed and analyzed for differential expression. Statistically significant genes were imported into Ingenuity Pathway Analysis (IPA) to identify either therapeutics or genomic targets using the Causal network analysis and Upstream regulator functions. All drug combinations were tested in their respective cell lines and cell viability was assessed via Celltiter-Fluor. Synergy of the combinations was calculated using the Chou-Talalay method.

Results: Using genomically chosen hard targets for drug combinations, all eight cell lines displayed additive or antagonistic results except low nanomolar doses for the MDA-MB-231 cell line. Dosing of MDA-MB-231s with Debrafinib and Pazopanib however, turned highly antagonistic as dosing increased. Using next-generation RNA sequencing data of TNBCs, IPA analysis identified several compensatory targets for each cell line when treated with one of the primary genomically driven drug at its IC50. Using dose escalation of the new drugs with a single hard target drug, we found that each compensatory combination displayed a striking increase in synergy across all TNBC cell lines treated when compared to their original hard target combination.

Conclusion: RNA sequencing of TNBC cells lines treated with single therapies chosen by actionable genomic landscape has revealed compensatory pathways, indicating further druggable targets. These compensatory pathways have been observed to more efficacious in treating TNBC cell lines. Using therapeutics that are either FDA approved or in clinical trials we have found that each compensatory combination shows a higher level of synergy across all cell lines. These data show that choosing a secondary therapy based on compensatory pathways may outperform hard target combinations in the clinic.

Citation Format: Solzak J, Hancock B, Paul R, Radovich M. Precision therapeutic combinations are synergistic against triple negative breast cancer using compensatory pathways [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-10-03.

Abstract LB-138: TP53 mutation is a biomarker for prognosis in triple-negative breast cancer patients treated with post-neoadjuvant cisplatin

Introduction: Patients with Triple-Negative Breast Cancer (TNBC) who have residual disease (RD) after neoadjuvant chemotherapy (NAC) are at an increased risk of relapse and death. These patients display a marked diversity in outcome, thus markers that can predict prognosis would be of benefit. BRE09-146 was a Phase II post-neoadjuvant clinical trial testing Cisplatin + Rucaparib versus Cisplatin alone in TNBC patients with RD post-NAC. TP53 is mutated in 70-80% of TNBCs, but its prognostic potential has yet to be elucidated. Herein, we seek to comprehensively determine the prognostic capability of mutated TP53 to determine outcome with post-neoadjuvant Cisplatin in BRE09-146.

Methods: We performed sequence and copy number analysis of 134 genes in 76 tumors from BRE09-146 using the Oncomine Research Panel along with Ion Proton Next Generation Sequencing. All patients included had RD. Somatic mutations were called by identifying mutations that were present in the tumor that were not present in the germ line DNA from a normal blood sample. Mutations were annotated using the IARC TP53 somatic mutation database. Gene copy numbers in tumors were identified using the Ion Reporter System and called as copy number loss, normal, or gain based upon a comparison to a reference range established from the normal blood samples. Survival analyses were generated using Log-Rank and Kaplan-Meier statistics.

Results: TP53 was highly mutated in this patient cohort (92% incidence). TP53 copy loss was independently associated with disease-free survival (DFS) and overall survival (OS); DFS events = 50% vs. 34%; median = 19.09 mos. vs. NR (Not Reached); p = 0.03; HR = 2.27 (95% C.I.: 1.13-7.28); OS events = 40% vs. 37%; median = 24.02 mos. vs. NR; p = 0.02; HR = 2.64 (95% C.I.: 1.28-11.35). Cancers without a TP53 mutation or subclonal TP53 mutation (present in a fraction of cells) demonstrated superior OS; events = 40% vs. 10%; median = 29.14 mos. vs. NR; p = 0.005; HR = 6.00 (95% C.I.: 1.46-7.96). Likewise, cancers bearing compound mutations (point mutation plus loss-of-heterozygosity/copy loss) were correlated with inferior DFS and OS; DFS events = 50% vs. 26%; median = 19.09 mos. vs. NR; p = 0.009; HR = 2.64 (95% C.I.: 1.30-5.67); OS events = 45% vs. 16%; median = 24.02 mos. vs. NR; p = 0.0007; HR = 4.26 (95% C.I.: 1.89-10.01).

Conclusions: It is well-known that TP53 is heavily mutated in TNBC, yet to-date, realizing the prognostic potential for this marker has not been accomplished. We have demonstrated the prognostic signficance of TP53 mutations for TNBC patients with residual disease after NAC. Additionally, we have uncovered p53 dysfunction as a continuum in this patient population in which cancers with higher degrees of dysfunction are correlated with a poorer prognosis and cancers with less dysfunction a superior prognosis.

Citation Format: Bradley Hancock, Yu-Hsiang Chen, Jeffrey Solzak, Kathy Miller, Milan Radovich. TP53 mutation is a biomarker for prognosis in triple-negative breast cancer patients treated with post-neoadjuvant cisplatin. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-138.