Everolimus in combination with vandetanib in children, adolescents, and young adults: a phase I study

BACKGROUND

Combined use of inhibitors of mammalian target of rapamycin (mTOR) and vascular endothelial growth factor (VEGF-2) receptors is a potential strategy to overcome resistance to either class of drugs when used alone.

PATIENTS AND METHODS

We designed a phase 1 trial to test the drug combination of a multikinase VEGF receptor 2 inhibitor, vandetanib, and an mTOR inhibitor, everolimus, in a pediatric and young adult patient cohort with advanced cancers. Exceptional responders were probed for tumor mutational profile to explore possible molecular mechanisms of response.

RESULTS

Among 21 enrolled patients, clinical benefit was observed in 38% (one patient with partial response and eight patients with stable disease) with a median progression-free survival of 3.3 months. The most common treatment-related adverse event was rash (n = 13). Other treatment-related toxicities included diarrhea, fatigue, hypertension, QT prolongation, hypertriglyceridemia/hypercholesterolemia, transaminitis, thrombocytopenia, and weight loss. None of the patients experienced dose-limiting toxicities. Three exceptional responders were analyzed and were found to harbor genetic alterations including kinase insert domain receptor (KDR) Q472H mutation, EWSR1-CREB3L1, CDKN2A/B loss, and ASPL/ASPSCR1-TFE3 fusion.

CONCLUSIONS

The combination of vandetanib and everolimus showed early activity and tolerable toxicity profile in pediatric patients with advanced cancers.

HER2-low expression in patients with advanced or metastatic solid tumors

BACKGROUND

Human epidermal growth factor receptor 2 (HER2)-low is a newly defined category with HER2 1+ or 2+ expression by immunohistochemistry (IHC) and lack of HER2 gene amplification measured by in situ hybridization (ISH). Much remains unknown about the HER2-low status across tumor types and changes in HER2 status between primary and metastatic samples.

PATIENTS AND METHODS

HER2 expression by IHC was evaluated in 4701 patients with solid tumors. We have evaluated the HER2 expression by IHC and amplification by ISH in paired breast and gastric/gastroesophageal (GEJ) primary and metastatic samples. HER2 expression was correlated with ERBB2 genomic alterations evaluated by next-generation sequencing (NGS) in non-breast, non-gastric/GEJ samples.

RESULTS

HER2 expression (HER2 IHC 1-3+) was found in half (49.8%) of the cancers, with HER2-low (1 or 2+) found in many tumor types: 47.1% in breast, 34.6% in gastric/GEJ, 50.0% in salivary gland, 46.9% in lung, 46.5% in endometrial, 46% in urothelial, and 45.5% of gallbladder cancers. The concordance evaluation of HER2 expression between primary and metastatic breast cancer samples showed that HER2 3+ remained unchanged in 87.1% with a strong agreement between primary and metastatic samples, with a weighted kappa (Κ) of 0.85 (95% confidence interval 0.79-0.91). ERBB2 alterations were identified in 117 (7.5%) patients with non-breast, non-gastric/GEJ solid tumors who had NGS testing. Of 1436 patients without ERBB2 alterations, 512 (35.7%) showed any level HER2 expression by IHC.

CONCLUSION

Our results show that HER2-low expression is frequently found across tumor types. These findings suggest that many patients with HER2-low solid tumors might benefit from HER2-targeted therapies.

Ultrasensitive detection of BRAF mutations in circulating tumor DNA of non-metastatic melanoma

Background

Implementation of adjuvant therapies in non-metastatic melanoma improved treatment outcomes in some patients; however, adjuvant therapy can be associated with significant cost and risk of toxicity. Therefore, there is an unmet need to better identify patients at high risk of recurrence.

Patients and methods

We carried out an ultrasensitive droplet digital PCR (ddPCR)-based detection of BRAF^V600E-mutated circulating tumor DNA (ctDNA) from blood samples prospectively collected before surgery, 1 hour after surgery, and then serially during follow-up.

Results

In 80 patients (stages ≤III), BRAF^V600E mutations were detected in 47.2% of tissue, in 37.7% of ctDNA samples collected before surgery, and in 25.9% of ctDNA samples collected 1 hour after surgery. Patients with detected ctDNA in blood collected 1 hour after surgery compared to patients without detected ctDNA had higher likelihood of melanoma recurrence (P < 0.001) and shorter median disease-free survival (P = 0.001) and overall survival (P = 0.003).

Conclusions

Ultrasensitive ddPCR can detect ctDNA in pre- and post-surgical blood samples from patients with resectable melanoma. Detection of ctDNA in post-surgical samples is associated with inferior treatment outcomes.

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Ultrasensitive ddPCR can detect ctDNA in pre- and post-surgical samples.

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Detection of ctDNA 1 hour after surgery is associated with inferior treatment outcomes.

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There were no associations between ctDNA detection at other timepoints and clinical outcomes.

PIK3CA mutations in plasma circulating tumor DNA predict survival and treatment outcomes in patients with advanced cancers

Background

Oncogenic mutations in PIK3CA are prevalent in diverse cancers and can be targeted with inhibitors of the phosphoinositide-3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway. Analysis of circulating tumor DNA (ctDNA) provides a minimally invasive approach to detect clinically actionable PIK3CA mutations.

Patients and methods

We analyzed PIK3CA hotspot mutation frequency by droplet digital PCR (QX 200; BioRad) using 16 ng of unamplified plasma-derived cell-free DNA from 68 patients with advanced solid tumors (breast cancer, n = 41; colorectal cancer, n = 13; other tumor types, n = 14). Results quantified as variant allele frequencies (VAFs) were compared with previous testing of archival tumor tissue and with patient outcomes.

Results

Of 68 patients, 58 (85%) had PIK3CA mutations in tumor tissue and 43 (74%) PIK3CA mutations in ctDNA with an overall concordance of 72% (49/68, κ = 0.38). In a subset analysis, which excluded samples from 26 patients known not to have disease progression at the time of sample collection, we found an overall concordance of 91% (38/42; κ = 0.74). PIK3CA-mutated ctDNA VAF of ≤8.5% (5% trimmed mean) showed a longer median survival compared with patients with a higher VAF (15.9 versus 9.4 months; 95% confidence interval 6.7-17.1 months; P = 0.014). Longitudinal analysis of ctDNA in 18 patients with serial plasma collections (range 2-22 time points, median 5) showed that those with a decrease in PIK3CA VAF had a longer time to treatment failure (TTF) compared with patients with an increase or no change (10.7 versus 2.6 months; P = 0.048).

Conclusions

Detection of PIK3CA mutations in ctDNA is concordant with testing of archival tumor tissue. Low quantity of PIK3CA-mutant ctDNA is associated with longer survival and a decrease in PIK3CA-mutant ctDNA on therapy is associated with longer TTF.

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Testing for PIK3CA mutations in ctDNA is concordant with testing of tumor tissue.

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High PIK3CA-mutant abundance in ctDNA was associated with shorter survival.

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Increasing PIK3CA-mutant abundance in serial blood samples was associated with shorter TTF.

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Longitudinal monitoring of PIK3CA-mutant ctDNA tracked with cancer clinical course.

Safety and activity of vandetanib in combination with everolimus in patients with advanced solid tumors: a phase I study

Background

Preclinical studies suggest that combining vandetanib (VAN), a multi-tyrosine kinase inhibitor of rearranged during transfection (RET) proto-oncogene, vascular endothelial growth factor receptor (VEGFR), and epidermal growth factor receptor (EGFR), with everolimus (EV), a mammalian target of rapamycin (mTOR) inhibitor, may improve antitumor activity. We determined the safety, maximum tolerated dose (MTD), recommended phase II dose (RP2D), and dose-limiting toxicities (DLTs) of VAN + EV in patients with advanced solid cancers and the effect of combination therapy on cancer cell proliferation and intracellular pathways.

Patients and methods

Patients with refractory solid tumors were enrolled in a phase I dose-escalation trial testing VAN (100-300 mg orally daily) + EV (2.5-10 mg orally daily). Objective responses were evaluated using RECIST v1.1. RET mutant cancer cell lines were used in cell-based studies.

Results

Among 80 patients enrolled, 72 (90%) patients were evaluable: 7 achieved partial response (PR) (10%) and 37 had stable disease (SD) (51%; duration range: 1-27 cycles). Clinical benefit (SD or PR ≥ 6 months) was observed in 26 evaluable patients [36%, 95% confidence intervals (CI) (25% to 49%)]. In 80 patients, median overall survival (OS) was 10.5 months [95% CI (8.5-16.1)] and median progression-free survival (PFS) 4.1 months [95% CI (3.4-7.3)]. Six patients (7.5%) experienced DLTs and 20 (25%) required dose modifications. VAN + EV was safe, with fatigue, rash, diarrhea, and mucositis being the most common toxicities. In cell-based studies, combination therapy was superior to monotherapy at inhibiting cancer cell proliferation and intracellular signaling.

Conclusions

The MTDs and RP2Ds of VAN + EV are 300 mg and 10 mg, respectively. VAN + EV combination is safe and active in refractory solid tumors. Further investigation is warranted in RET pathway aberrant tumors.

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VAN + EV is safe, active and provides clinical benefit in some patients with refractory solid cancers.

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Dual therapy is superior to monotherapy at inhibiting proliferation and intracellular signaling of RET mutant cancer cells.

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This study highlights the importance of identifying novel combination therapies to overcome therapeutic resistance.

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Next-generation sequencing of advanced solid tumors may inform treatment strategies and guide future drug development.

Structural basis of acquired resistance to selpercatinib and pralsetinib mediated by non-gatekeeper RET mutations

BACKGROUND

Selpercatinib (LOXO-292) and pralsetinib (BLU-667) are highly potent RET-selective protein tyrosine kinase inhibitors (TKIs) for treating advanced RET-altered thyroid cancers and non-small-cell lung cancer (NSCLC). It is critical to analyze RET mutants resistant to these drugs and unravel the molecular basis to improve patient outcomes.

PATIENTS AND METHODS

Cell-free DNAs (cfDNAs) were analyzed in a RET-mutant medullary thyroid cancer (MTC) patient and a CCDC6-RET fusion NSCLC patient who had dramatic response to selpercatinib and later developed resistance. Selpercatinib-resistant RET mutants were identified and cross-profiled with pralsetinib in cell cultures. Crystal structures of RET-selpercatinib and RET-pralsetinib complexes were determined based on high-resolution diffraction data collected with synchrotron radiation.

RESULTS

RETG810C/S mutations at the solvent front and RETY806C/N mutation at the hinge region were found in cfDNAs of an MTC patient with RETM918T/V804M/L, who initially responded to selpercatinib and developed resistance. RETG810C mutant was detected in cfDNAs of a CCDC6-RET-fusion NSCLC patient who developed acquired resistance to selpercatinib. Five RET kinase domain mutations at three non-gatekeeper residues were identified from 39 selpercatinib-resistant cell lines. All five selpercatinib-resistant RET mutants were cross-resistant to pralsetinib. X-ray crystal structures of the RET-selpercatinib and RET-pralsetinib complexes reveal that, unlike other TKIs, these two RET TKIs anchor one end in the front cleft and wrap around the gate wall to access the back cleft.

CONCLUSIONS

RET mutations at the solvent front and the hinge are resistant to both drugs. Selpercatinib and pralsetinib use an unconventional mode to bind RET that avoids the interference from gatekeeper mutations but is vulnerable to non-gatekeeper mutations.

Recommendations for the use of next-generation sequencing (NGS) for patients with metastatic cancers: a report from the ESMO Precision Medicine Working Group

Next-generation sequencing (NGS) allows sequencing of a high number of nucleotides in a short time frame at an affordable cost. While this technology has been widely implemented, there are no recommendations from scientific societies about its use in oncology practice. The European Society for Medical Oncology (ESMO) is proposing three levels of recommendations for the use of NGS. Based on the current evidence, ESMO recommends routine use of NGS on tumour samples in advanced non-squamous non-small-cell lung cancer (NSCLC), prostate cancers, ovarian cancers and cholangiocarcinoma. In these tumours, large multigene panels could be used if they add acceptable extra cost compared with small panels. In colon cancers, NGS could be an alternative to PCR. In addition, based on the KN158 trial and considering that patients with endometrial and small-cell lung cancers should have broad access to anti-programmed cell death 1 (anti-PD1) antibodies, it is recommended to test tumour mutational burden (TMB) in cervical cancers, well- and moderately-differentiated neuroendocrine tumours, salivary cancers, thyroid cancers and vulvar cancers, as TMB-high predicted response to pembrolizumab in these cancers. Outside the indications of multigene panels, and considering that the use of large panels of genes could lead to few clinically meaningful responders, ESMO acknowledges that a patient and a doctor could decide together to order a large panel of genes, pending no extra cost for the public health care system and if the patient is informed about the low likelihood of benefit. ESMO recommends that the use of off-label drugs matched to genomics is done only if an access programme and a procedure of decision has been developed at the national or regional level. Finally, ESMO recommends that clinical research centres develop multigene sequencing as a tool to screen patients eligible for clinical trials and to accelerate drug development, and prospectively capture the data that could further inform how to optimise the use of this technology.

Phase I, first-in-human study of futibatinib, a highly selective, irreversible FGFR1-4 inhibitor in patients with advanced solid tumors

BACKGROUND

Futibatinib is an oral, irreversible, highly selective fibroblast growth factor receptor (FGFR)1-4 inhibitor with potent preclinical activity against tumors harboring FGFR aberrations. This first-in-human, phase I dose-escalation trial (NCT02052778) evaluates the safety and pharmacokinetics/pharmacodynamics of futibatinib in advanced solid tumors.

PATIENTS AND METHODS

Following a standard 3+3 dose-escalation design, eligible patients with advanced solid tumors refractory to standard therapies received 8-200 mg futibatinib three times a week (t.i.w.) or 4-24 mg once daily (q.d.).

RESULTS

A total of 86 patients were enrolled in the nine t.i.w. (n = 42) and five q.d. cohorts (n = 44); 71 patients (83%) had tumors harboring FGF/FGFR aberrations. Three of nine patients in the 24-mg q.d. cohort experienced dose-limiting toxicities, including grade 3 increases in alanine transaminase, aspartate transaminase, and blood bilirubin (n = 1 each). The maximum tolerated dose (MTD) was determined to be 20 mg q.d.; no MTD was defined for the t.i.w. schedule. Across cohorts (n = 86), the most common treatment-emergent adverse events (TEAEs) were hyperphosphatemia (59%), diarrhea (37%), and constipation (34%); 48% experienced grade 3 TEAEs. TEAEs led to dose interruptions, dose reductions, and treatment discontinuations in 55%, 14%, and 3% of patients, respectively. Pharmacokinetics were dose proportional across all q.d. doses but not all t.i.w. doses evaluated, with saturation observed between 80 and 200 mg t.i.w. Serum phosphorus increased dose dependently with futibatinib on both schedules, but a stronger exposure-response relationship was observed with q.d. dosing, supporting 20 mg q.d. as the recommended phase II dose (RP2D). Overall, partial responses were observed in five patients [FGFR2 fusion-positive intrahepatic cholangiocarcinoma (n = 3) and FGFR1-mutant primary brain tumor (n = 2)], and stable disease in 41 (48%).

CONCLUSIONS

Futibatinib treatment resulted in manageable safety, pharmacodynamic activity, and preliminary responses in patients with advanced solid tumors. The results of this phase I dose-escalation trial support 20 mg q.d. futibatinib as the RP2D.

CLINICAL TRIAL REGISTRATION

FOENIX-101 (ClinicalTrials.gov, NCT02052778).

Targeted therapy for advanced salivary gland carcinoma based on molecular profiling: results from MyPathway, a phase IIa multiple basket study

BACKGROUND

Systemic therapy options for salivary cancers are limited. MyPathway (NCT02091141), a phase IIa study, evaluates targeted therapies in non-indicated tumor types with actionable molecular alterations. Here, we present the efficacy and safety results for a subgroup of MyPathway patients with advanced salivary gland cancer (SGC) matched to targeted therapies based on tumor molecular characteristics.

PATIENTS AND METHODS

MyPathway is an ongoing, multiple basket, open-label, non-randomized, multi-center study. Patients with advanced SGC received pertuzumab + trastuzumab (HER2 alteration), vismodegib (PTCH-1/SMO mutation), vemurafenib (BRAF V600 mutation), or atezolizumab [high tumor mutational burden (TMB)]. The primary endpoint is the objective response rate (ORR).

RESULTS

As of January 15, 2018, 19 patients with SGC were enrolled and treated in MyPathway (15 with HER2 amplification and/or overexpression and one each with a HER2 mutation without amplification or overexpression, PTCH-1 mutation, BRAF mutation, and high TMB). In the 15 patients with HER2 amplification/overexpression (with or without mutations) who were treated with pertuzumab + trastuzumab, 9 had an objective response (1 complete response, 8 partial responses) for an ORR of 60% (9.2 months median response duration). The clinical benefit rate (defined by patients with objective responses or stable disease >4 months) was 67% (10/15), median progression-free survival (PFS) was 8.6 months, and median overall survival was 20.4 months. Stable disease was observed in the patient with a HER2 mutation (pertuzumab + trastuzumab, n = 1/1, PFS 11.0 months), and partial responses in patients with the PTCH-1 mutation (vismodegib, n = 1/1, PFS 14.3 months), BRAF mutation (vemurafenib, n = 1/1, PFS 18.5 months), and high TMB (atezolizumab, n = 1/1, PFS 5.5+ months). No unexpected toxicity occurred.

CONCLUSIONS

Overall, 12 of 19 patients (63%) with advanced SGC, treated with chemotherapy-free regimens matched to specific molecular alterations, experienced an objective response. Data from MyPathway suggest that matched targeted therapy for SGC has promising efficacy, supporting molecular profiling in treatment determination.

Abstract OT1-03-04: INTERACT- INTegrated Evaluation of Resistance and Actionability using Circulating Tumor DNA in hormone receptor (HR) positive metastatic breast cancers (MBC)

Background

Mutations in the ligand-binding domain of ESR1 have been demonstrated to mediate resistance to aromatase inhibitors (AI) and are associated with poor survival. Analyses of circulating tumor DNA (ctDNA) offer a minimally invasive and real-time approach to characterize genomic landscape, clonal evolution, and treatment response. Early detection and intervention with alternate therapy to overcome resistance at minimal disease burden progression could have a larger impact than treating higher burden disease at clinical progression. However, whether treatment decisions made based on the emergence of secondary resistance mutations or mutant allele fraction (MAF) changes in ctDNA can improve clinical outcomes is unknown. Currently, the most effective therapy for patients harboring ESR1 mutations is unclear; although, pre-clinical and retrospective clinical trial analyses have suggested that some of these mutations may exhibit greater sensitivity to fulvestrant, a selective estrogen receptor down-regulator, compared to AI. This study hypothesizes that real-time monitoring of ctDNA for secondary ESR1 alterations can identify subclinical progression and early intervention with a targeted-agent that has greater efficacy against ESR1 mutations can improve disease-free survival.

Trial Design

This is a randomized, open-label, Phase-2 study for HR-positive MBC patients who are on AI and CDK 4/6 inhibitor as first line therapy. Patients on treatment for at least 12 months without evidence of clinical progression would be screened for ESR1 mutations using Guardant360 ctDNA assay. Patients with positive ESR1 mutations would be randomized to change of endocrine therapy to fulvestrant vs. continuing AI.

Eligibility criteria

-Histologically confirmed HR-positive (ER and/or PR &gt;10%) and HER2-negative MBC

-On AI with CDK4/6 inhibitor as first line therapy for 12 months without evidence of clinical progression

-Activating ESR1 mutation identified on ctDNA

-ECOG performance status ≤1

-Normal organ and marrow function

Specific aims

- To assess progression-free survival (PFS) with transition to fulvestrant compared with continuing AI therapy in patients with emergence of ESR1 mutations in plasma

-To assess ctDNA ESR1 mutant allele fraction and kinetics with transition to fulvestrant compared with AI

-To assess the prevalence of ESR1 mutations in patients with exposure to endocrine therapy

-To assess overall survival with fulvestrant transition compared with continuing AI therapy in patients with emergence of ESR1 mutations

Statistical methods

To detect a change in median PFS from 5 months (for AI arm) to 9 months (with fulvestrant arm) would require about 124 patients (5% two-sided alpha, 80% power, log rank testing). Interim analysis will be performed when 42 PFS events are observed. Using O'Brien-Fleming stopping boundaries, we will stop for futility if the log rank test p-value &gt; 0.72 and stop for success if it is &lt; 0.004.

Citation Format: Damodaran S, Meric-Bernstam F, Hess KR, Litton JK, Raymond V, Lanman R, Ueno NT, Hamilton S, Wistuba II, Valero V, Moulder SL, Tripathy D. INTERACT- INTegrated Evaluation of Resistance and Actionability using Circulating Tumor DNA in hormone receptor (HR) positive metastatic breast cancers (MBC) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT1-03-04.

Abstract P6-20-12: FGFR1β is a driver isoform of FGFR1 alternative splicing in breast cancer cells

Background:Abnormal FGFR1 alternative splicing is correlated with tumorigenicity and poor prognosis in several tumor types. We sought to determine the roles of FGFR1α and FGFR1β variants in breast cancer. Methods: TCGA breast cancer samples and cell lines were analyzed for FGFR1α and FGFR1β expression. MCF-10A cells were used to overexpress these variants. Cell growth was assessed by SRB and colony formation assays. Cell transformation was assessed by 3D-Matrigel, soft agar, cell motility assays. Cell survival assay was used to determine drug IC50. Results: In the TCGA, compared to FGFR1 non-amplified samples, FGFR1-amplified samples had significantly higher FGFR1α, but not FGR1β levels. FGFR1β expression levels and FGFR1β/FGFR1α ratio were higher in basal subtype samples than in luminal samples in both the TCGA and in a panel of breast cancer cell lines. Both FGFR1α and FGFR1b induced transformation of MCF-10A cells. However, only FGFR1β-expressing cells, not FGFR1α, enhanced cell growth, cell motility, and FGFR signaling. Cells with higher FGFR1β levels and FGFR1β/FGFR1α ratio were more sensitive to FGFR inhibitor BGJ-398. Interestingly, in ER-negative cells, BGJ-398 decreased FGFR1β levels, likely by increasing expression of splicing repressor PTBP1. In ER-positive cells, estrogen treatment increased FGFR1β levels by decreasing PTBP1 expression, which was blocked by 4-OHT. Lastly, combination treatment with BGJ-398 and 4-OHT synergistically inhibited cell survival. Conclusions: These findings suggest that FGFR1 alternative splicing plays an important role in breast cancer, where FGFR1β functions as a driver isoform. Further work is needed to assess FGFR1β prognostic and predictive role.

Citation Format: Zhao M, Zhuo M-L, Zheng X, Su X, Meric-Bernstam F. FGFR1β is a driver isoform of FGFR1 alternative splicing in breast cancer cells [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-20-12.

Abstract P4-04-08: Genomic profiling of 304 treatment-naïve Chinese breast cancer patients: A comparison of Chinese and TCGA cohorts

Background: The complexity of BC at the clinical, morphological and molecular level has been well recognized. Molecular profiling, which reveals the intrinsic biology among subtypes, has significantly advanced the management of this disease. However, previous studies have provided very limited molecular data on Chinese breast cancer patients.

Methods: We performed targeted sequencing using a panel consisting of 36 BC related genes to interrogate the genomic landscape of 304 consecutive treatment-naïve Chinese BC patients and compared our results to the TCGA data set.

Results: Comparing to TCGA, our cohort had significantly fewer patients with triple negative breast cancer (8.2% vs 15.5% p=0.002). The most prominent genomic difference was our cohort had significantly higher TP53mutation frequency in HR+/HER2- and HR+/HER2+ groups. The composition of TP53 mutations also differed significantly between two cohorts in HR+/HER2- group, with TCGA cohort having missense mutation as the predominant mutation; whereas, in our cohort, nonsense and frameshift mutations were predominant. We classified the most populated and diverse group of HR+/HER2- cancer into 4 subgroups based on molecular signature. The clinical significance of this proposed classification was confirmed by differences in overall survival using data from the TCGA.

Conclusions:We identified distinctive genomic patterns associated with Chinese breast cancer patients compared to TCGA data, suggesting the importance of mutation-based stratification according to ethnic status. To the best of our knowledge, this is one of the largest study of Chinese BC patients that interrogated the spectrum of mutational events and correlated these molecular signatures with clinical outcomes.

This study was supported by funding from National Natural Science Foundation of China (Grant No. 81602645), Guangdong Provincial Natural Science Foundation (Grant No. 2016A030313768) and Research Funds from Guangzhou Science and Technology Bureau (Grant No. 201707010418 and 201804010430).

Citation Format: Liao N, Zhang G, Wang Y, Guo L, Cao L, Zhang Z, Balch CM, Meric-Bernstam F. Genomic profiling of 304 treatment-naïve Chinese breast cancer patients: A comparison of Chinese and TCGA cohorts [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-04-08.

Abstract P6-21-04: Targeting PI3Kβ alone and in combination with chemotherapy or immunotherapy in tumors with PTEN loss

Background: PTEN functions as a negative regulator of the phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR pathway to promote balanced cell proliferation, survival and differentiation. PTEN loss occurs across a variety of cancer subtypes; PTEN-deficient tumors are dependent on PI3Kβ activity, making PI3Kβ a compelling target. We evaluated the efficacy of PI3Kβ inhibitor AZD8186 as a single agent and in combination with standard chemotherapy and immune checkpoint inhibitors focused on tumors with loss of PTEN function.

Methods: In vitro, cell proliferation assays were performed to determine the half maximal inhibitory concentration (IC50) after 3 days of treatment and to test the effects in combination with standard chemotherapy. Colony formation assays were performed to confirm efficacy of AZD8186 in PTEN-deficient cell lines. Western blot analysis was performed to assess PTEN protein expression and to evaluate effects of AZD8186 on PI3K signaling. In vivo, antitumor efficacy of AZD8186 as a single agent as well as in combination with paclitaxel and anti-PD1 was evaluated.

Results: AZD8186 inhibited the cell proliferation of three of ten TNBC cell lines in vitro; PTEN loss was significantly correlated with AZD8186 sensitivity (p= 0.008). Colony formation assay confirmed sensitivity of PTEN-deficient cell lines to AZD8186. AZD8186 inhibited PI3K signaling with decreased expression of pAKT, pGSK3β, pPRAS40 and pS6. AZD8186 treatment of PTEN-deficient cell lines, MDA-MB-436 and MDA-MB-468, resulted in increased apoptosis. Cell proliferation assays demonstrated additive effect of the combination of paclitaxel with AZD8186. AZD8186 significantly enhanced antitumor activity of paclitaxel in MDA-MB-436 and MDA-MB-468 cell-line-derived xenografts, with disease stabilization in the latter. In syngeneic models, AZD8186 enhanced antitumor efficacy of anti-PD1 antibodies in PTEN-deficient BP murine melanoma xenograft (p=0.0073), but not in PTEN-wildtype colon carcinoma, CT26.

Conclusion: AZD8186 has single agent efficacy in PTEN-deficient triple negative breast cancer cell lines in vitro, with modest single agent efficacy in vivo. AZD8186 enhanced the antitumor efficacy of paclitaxel and of Anti-PD1 antibodies in vivo. Further study is needed to determine optimal combination therapies for PTEN-deficient solid tumors.

Citation Format: Owusu-Brackett N, Zhao M, Akcakanat A, Evans KW, Yuca E, Tapia C, Ileana-Dumbrava E, Janku F, Meric-Bernstam F. Targeting PI3Kβ alone and in combination with chemotherapy or immunotherapy in tumors with PTEN loss [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-21-04.

Abstract P1-13-04: Efficacy of adjuvant 5-Fluorouracil in residual HER2-negative breast cancer following neoadjuvant chemotherapy

Background: Patients with residual disease following neoadjuvant chemotherapy have an increased risk of relapse. Recently the CREATE-X trial demonstrated that adjuvant capecitabine (oral prodrug of 5'deoxy-5-fluorouridine), prolonged disease-free survival and overall survival among patients with HER2-negative breast cancer who had residual invasive disease after neoadjuvant chemotherapy containing anthracycline, taxane, or both. Therefore, we sought to evaluate the antitumor efficacy of 5-fluorouracil (5-FU) in patient-derived xenografts (PDXs) from residual tumors resistant to neoadjuvant chemotherapy.

Methods: Antitumor efficacy of 5-FU was assessed in vivo in three PDXs varying in hormone receptor status (0, 4% and 11% respectively), generated from residual tumors of primary breast cancer patients treated with neoadjuvant chemotherapy containing anthracycline, and taxanes. In addition, significance of timing of therapy was also assessed, comparing efficacy of initiating treatment upon implantation (immediate start cohort; mimicking treating residual disease with adjuvant therapy), with initiating treatment upon establishment of PDX (standard start cohort).

Results: 5-FU was efficacious in established PDX models that are triple negative (0% ER; p&lt; 0.0001), low ER positive (4% ER, p=0.0213) and ER-positive (11% ER; p= 0.0390), decreasing growth compared to the cohort. However, there was no statistically significant difference between the immediate start cohort and standard start cohort. Western blot analysis of the treatment-naïve derived mouse tumors recognized RB as a predictive biomarker for 5-FU response.

Conclusion: 5-FU has anti-tumor activity in residual HER2-negative PDX models resistant to taxanes, and anthracyclines in the neoadjuvant setting.

Citation Format: Owusu-Brackett N, Scott S, Yuca E, Evans KW, Tapia C, Meric-Bernstam F. Efficacy of adjuvant 5-Fluorouracil in residual HER2-negative breast cancer following neoadjuvant chemotherapy [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-13-04.

Abstract P6-18-13: Identification of optimal combination therapy partners for PI3K/Akt/mTOR pathway inhibitor in triple negative breast cancer

Triple-negative breast cancer (TNBC) is among the most aggressive subtypes, accounts for 10-15% of all breast cancer cases and is characterized by a lack of hormone receptors with a low overall survival rate. Due to the heterogeneity nature of this disease, the absence of validated molecular targets makes it unresponsive to conventional therapies. PI3K/Akt/mTOR pathway is aberrantly activated in TNBC, but single agent therapy is commonly subject to resistance. The goal of this study is to identify the genes that can be targeted to enhance the efficacy of mTOR inhibitor TAK228, an agent that is being investigated as a treatment for advanced solid tumors, in TNBC with PI3K pathway activation. We utilized an in vivo pooled barcoded shRNA library screening to determine the genes that have the potential to be used as TAK228 synthetic lethal partners. Using deep sequencing analysis of the shRNA profiles, we identified several genes whose loss of function conferred synthetic lethality in the presence of TAK228. We found that targeting the candidate genes (WEE1, BMX and MAPK15) with their inhibitors (AZD1775, Ibrutinib and Sunitinib) did not significantly affect the viability, however combination treatment of these agents with TAK228 induced a robust growth inhibition and demonstrated a significant synergy in MDA-MB-468 cell lines. Investigating the activation of relevant survival signaling pathways will further elucidate the mechanism of synthetic lethal interaction. These observations provide a promising rational strategy for the treatment of TNBC with PI3K pathway aberration.

Citation Format: Shariati M, Paez-Arango N, Bristow CA, Evans KW, Peoples MD, Carugo A, Heffernan TP, Meric-Bernstam F. Identification of optimal combination therapy partners for PI3K/Akt/mTOR pathway inhibitor in triple negative breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-18-13.

Abstract PD3-06: Neratinib + fulvestrant for HER2-mutant, HR-positive, metastatic breast cancer: Updated results from the phase 2 SUMMIT trial

Background: HER2 mutations define a rare subset of metastatic breast cancer (MBC) with a unique mechanism of oncogenic addiction to HER2 signaling. Neratinib, an irreversible pan-HER tyrosine kinase inhibitor, has demonstrated single-agent clinical activity in HER2-mutant MBC. In HER2-mutant, HR+ MBC, neratinib + fulvestrant (N+F) appears synergistic vs single-agent neratinib, possibly due to more complete inhibition of bi-directional signaling between HER2 and estrogen receptors. Here we describe interim efficacy results of the expanded HER2-mutant, HR+ MBC cohort treated with N+F from SUMMIT (NCT01953926).

Methods: HR+ MBC patients (pts) with HER2 mutations documented by local testing received oral neratinib 240mg qd and intramuscular fulvestrant (labeled dose). Intensive loperamide prophylaxis was mandatory during cycle 1. Efficacy endpoints include objective response rate at week 8 (ORR8); confirmed objective response rate (ORR); clinical benefit rate (CBR); duration of response (DOR); progression-free survival (PFS); response was assessed by RECIST 1.1 and/or PET Response Criteria. Genomic profiling from fresh/archival tumor tissues and/or plasma cfDNA was performed retrospectively by next-generation sequencing (MSK-IMPACT).

Results: As of 18 May 2018, 46 HER2-mutant HR+ MBC pts have been treated with N+F. Most pts were pretreated, with 91% having received prior anti-cancer medication for MBC (range 0–10). ORR was 33% and median DOR in the 15 pts with a confirmed response was 9.2 months (95% CI 3.9–18.5). Twenty-four pts had prior fulvestrant exposure, and 19 had received prior CDK4/6i-based therapy. Clinical activity was observed with ORRs of 17% and 26% in prior fulvestrant-treated and prior CDK4/6i-treated pts, respectively. ORRs by HER2 mutation were: V777L 63% (5/8 pts); S310F/Y 67% (4/6 pts); G778_P780dup 50% (3/6 pts). Diarrhea was the most common adverse event (grade 3, 24%; grade 4, 0%). Median cumulative duration of grade 3 diarrhea was 3 days. There were no treatment discontinuations due to diarrhea.

 Neratinib + fulvestrantOutcomeaAll patients (N=46)Prior fulvestrant (N=24)Prior CDK4/6i-based therapy (N=19)ORR8 – n (%)19 (41.3)8 (33.3)7 (36.8)95% CI27.0–56.815.6–55.316.3–61.6ORR – n (%)15 (32.6)4 (16.7)5 (26.3)95% CI19.5–48.04.7–37.49.1–51.2DOR for each responder, months 5.6b; 9.2; 9.6b; 18.55.6b; 5.7b; 9.3; 9.6b; 12.9bCBR – n (%)27 (58.7)11 (45.8)9 (47.4)95% CI43.2–73.025.6–67.224.4–71.1Median (95% CI) time to event,c monthsPFS3.9 (3.6–5.7)3.7 (3.5–12.8)3.9 (1.9–NA)DOR9.2 (3.9–18.5)NANAaFor pts with both RECIST- and PET-evaluable lesions, the best of either RECIST or PET response was used to determine response; the earliest progression by RECIST or PET was used for progression; bPt has not progressed; cKaplan-Meier analysis; NA, not applicable

Conclusions: N+F demonstrates encouraging clinical activity with durable responses in heavily pretreated pts with HER2-mutant, HR+ MBC. Of note, responses were observed in pts who had received prior fulvestrant or CDK4/6 inhibitors. No new safety signals were identified; the rate of diarrhea was similar to single-agent neratinib and not dose limiting. Updated data after additional follow-up and genomic data will be presented.

Citation Format: Smyth LM, Piha-Paul SA, Saura C, Loi S, Lu J, Shapiro GI, Juric D, Mayer IA, Arteaga C, de la Fuente M, Brufksy AM, Mau-Sørensen M, Arnedos M, Moreno V, Sohn J-H, Schwartzberg L, Gonzàlez-Farré X, Cervantes A, Mann G, Shahin S, Cutler, Jr. RE, Eli LD, Xu F, Bagulho T, Lalani AS, Bryce R, Solit DB, Hyman DM, Meric-Bernstam F, Baselga J. Neratinib + fulvestrant for HER2-mutant, HR-positive, metastatic breast cancer: Updated results from the phase 2 SUMMIT trial [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD3-06.

Abstract P6-20-11: The stapled peptide ALRN-6924, a dual inhibitor of MDMX and MDM2, enhances antitumor efficacy of paclitaxel and Nab-paclitaxel in TP53 wild-type MCF-7 breast cancer models

Background: MDMX and MDM2 are endogenous inhibitors of the p53 tumor suppressor protein. MDMX levels are frequently elevated in luminal breast cancer, which generally expresses wild-type p53. ALRN-6924, an α-helical stapled peptide, is the first and only dual inhibitor of MDMX and MDM2 currently in clinical trials for solid tumors and hematological malignancies. We sought to determine the antitumor efficacy of the combination of ALRN-6924 with taxanes in models of human breast cancer.

Methods: Sulforhodamine B colorimetric assay was used to assess the cytotoxicity of the combination of ALRN-6924 with taxanes in vitro. Athymic nude mice were implanted with MCF-7 tumors and treated for four weeks with ALRN-6924 alone and in combination with paclitaxel in cremaphor (Taxol®, study #1) or a nanoparticle-albumin-bound (nab) formulation (Abraxane®, study #2). In study #1, ALRN-6924 (5, 10 mg/kg) was dosed twice weekly and paclitaxel (10, 15 mg/kg) was dosed weekly, with paclitaxel administered 6 h prior to ALRN-6924. In study #2, ALRN-6924 alone (5 mg/kg) was dosed twice weekly while nab-paclitaxel (15 mg/kg) was administered weekly in combination at -24h, -6h, 0h, +6h, or +24h relative to ALRN-6924 administration.

Results: ALRN-6924 was found to have synergistic activity with paclitaxel in both MCF-7 and ZR-75-1 cell lines in vitro (Combination index: 0.874 and 0.323 respectively). In in vivo study #1, the combination of ALRN-6924 and paclitaxel significantly inhibited MCF-7 tumor growth compared to either agent alone (p&lt;0.005). Paclitaxel 15 mg/kg + ALRN-6924 5 mg/kg resulted in the greatest tumor inhibition with average tumor size decreased by 13% at four weeks versus the starting size.

In study #2, the combination of nab-paclitaxel with ALRN-6924 administered -6h to +24h relative to nab-paclitaxel resulted in improved efficacy over either single agent and a significant increase in the number of tumor regressions (up to 6/10 with 3 consecutive measurements &lt;50% of starting volume) compared to nab-paclitaxel alone (1/10, p&lt;0.005). When ALRN-6924 was administered 24h prior to nab-paclitaxel, there was a marked decrease in efficacy and no tumor regressions were observed.

In both studies, drug treatments were well tolerated with no significant weight loss in mice.

Conclusion: The significant increase in efficacy observed with ALRN-6924 in combination with paclitaxel supports further evaluation in patients with breast cancer.

Citation Format: Pairawan SS, Yuca E, Evans K, Annis A, Narasimhan N, Sutton D, Carvajal LA, Ren J-G, Santiago S, Guerlavais V, Akcakanat A, Tapia C, Illeana Dumbrava EE, Aivado M, Meric-Bernstam F. The stapled peptide ALRN-6924, a dual inhibitor of MDMX and MDM2, enhances antitumor efficacy of paclitaxel and Nab-paclitaxel in TP53 wild-type MCF-7 breast cancer models [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-20-11.

Larotrectinib in adult patients with solid tumours: a multi-centre, open-label, phase I dose-escalation study

BACKGROUND

NTRK1, NTRK2 and NTRK3 gene fusions (NTRK gene fusions) occur in a range of adult cancers. Larotrectinib is a potent and highly selective ATP-competitive inhibitor of TRK kinases and has demonstrated activity in patients with tumours harbouring NTRK gene fusions.

PATIENTS AND METHODS

This multi-centre, phase I dose escalation study enrolled adults with metastatic solid tumours, regardless of NTRK gene fusion status. Key inclusion criteria included evaluable and/or measurable disease, Eastern Cooperative Oncology Group performance status 0-2, and adequate organ function. Larotrectinib was administered orally once or twice daily, on a continuous 28-day schedule, in increasing dose levels according to a standard 3 + 3 dose escalation scheme. The primary end point was the safety of larotrectinib, including dose-limiting toxicity.

RESULTS

Seventy patients (8 with tumours with NTRK gene fusions; 62 with tumours without a documented NTRK gene fusion) were enrolled to 6 dose cohorts. There were four dose-limiting toxicities; none led to study drug discontinuation. The maximum tolerated dose was not reached. Larotrectinib-related adverse events were predominantly grade 1; none were grade 4 or 5. The most common grade 3 larotrectinib-related adverse event was anaemia [4 (6%) of 70 patients]. A dose of 100 mg twice daily was recommended for phase II studies based on tolerability and antitumour activity. In patients with evaluable TRK fusion cancer, the objective response rate by independent review was 100% (eight of the eight patients). Eight (12%) of the 67 assessable patients overall had an objective response by investigator assessment. Median duration of response was not reached. Larotrectinib had limited activity in tumours with NTRK mutations or amplifications. Pharmacokinetic analysis showed exposure was generally proportional to administered dose.

CONCLUSIONS

Larotrectinib was well tolerated, demonstrated activity in all patients with tumours harbouring NTRK gene fusions, and represents a new treatment option for such patients.

CLINCALTRIALS.GOV NUMBER

NCT02122913.

OncotypeDX Recurrence Score Does Not Predict Nodal Burden in Clinically Node Negative Breast Cancer Patients

BACKGROUND

OncotypeDX recurrence score (RS)^® has been found to predict recurrence and disease-free survival in patients with node negative breast cancer. Whether RS is useful in guiding locoregional therapy decisions is unclear. We sought to evaluate the relationship between RS and lymph node burden.

METHODS

Patients with invasive breast cancer who underwent sentinel lymph node dissection from 2010 to 2015 were identified from a prospectively maintained database. Patients were excluded if they were clinically node positive or if they received neoadjuvant chemotherapy. RS was classified as low (< 18), intermediate (18-30), or high (> 30). The association between RS, lymph node burden, and disease recurrence was evaluated. Statistical analyses were performed in R version 3.4.0; p < 0.05 was considered significant.

RESULTS

A positive SLN was found in 168 (15%) of 1121 patients. Completion axillary lymph node dissection was performed in 84 (50%) of SLN-positive patients. The remaining 84 (50%) patients had one to two positive SLNs and did not undergo further axillary surgery. RS was low in 58.5%, intermediate in 32.6%, and high in 8.9%. RS was not associated with a positive SLN, number of positive nodes, maximum node metastasis size, or extranodal extension. The median follow-up was 23 months. High RS was not associated with locoregional recurrence (p = 0.07) but was significantly associated with distant recurrence (p = 0.0015).

CONCLUSIONS

OncotypeDX RS is not associated with nodal burden in women with clinically node-negative breast cancer, suggesting that RS is not useful to guide decisions regarding extent of axillary surgery for these patients.