Abstract P6-11-03: Association of systemic paclitaxel concentrations with severity and progression of paclitaxel-induced peripheral neuropathy

Background: Paclitaxel is commonly used in combination regimens in patients with early stage breast cancer, but its use is often limited by the development of severe paclitaxel-induced peripheral neuropathy (PIPN). Paclitaxel pharmacokinetics (PK), specifically the maximum paclitaxel concentration (Cmax) and amount of time the concentration remains above 0.05 µM (Tc>0.05), have been associated with occurrence of severe, clinician-documented (NCI CTCAE) neuropathy. Patient-reported outcomes are more reliable, sensitive, and responsive than clinician-documented neuropathy, particularly for subjective toxicities. The objective of this study was to confirm that paclitaxel PK predicts occurrence and progression of patient-reported PIPN.

Methods: This observational trial enrolled patients with early stage breast cancer receiving adjuvant/neoadjuvant weekly 1-hour paclitaxel infusions (80 mg/m2 x 12 cycles) at the University of Michigan Comprehensive Cancer Center. Patients with existing neuropathy or previous neuropathic chemotherapy treatment were excluded. Paclitaxel concentration was measured via liquid chromatograph/mass spectrometry (LC/MS) in plasma samples collected at the end of (Cmax) and 16-24 hours after (Tc>0.05) first infusion. Patient-reported neuropathy was collected (EORTC CIPN20) at baseline and each treatment cycle. The 8-item sensory subscale of the CIPN20 (CIPN8, range 8-32) was estimated for each patient and cycle of treatment to calculate the change from baseline (ΔCIPN8, range 0-24). The analysis was conducted using two approaches. In the first analysis, the cohort was stratified into cases and controls by the median ΔCIPN8 and in the second, each patient was described by the rate of change of CIPN8 per treatment cycle. The association of Cmax and Tc>0.05 with case/control definition was tested using Wilcoxon rank sum and t-tests. Associations with rate of change of CIPN8 were tested using linear regression.

Results: 60 patients were enrolled in this observational clinical study. The mean age was 52.4 years, 93% of patients were Caucasian, and 5% had diabetes diagnosis. At baseline there was very little patient-reported neuropathy (mean baseline CIPN8=8.3). The median ΔCIPN8 was 4. Patients with ΔCIPN8>4 had greater Cmax than patients with ΔCIPN8≤4 (p=0.010). In the regression modeling, there was a significant correlation between patient's Tc>0.05 and the rate of increase in ΔCIPN8 (r=0.28, p=0.03).

Conclusions: Our preliminary findings suggest that a single PK sample collected at the end of the first cycle (Cmax) or 16-24 hours later (Tc>0.05) are indicative of a patient's risk of experiencing PIPN during paclitaxel treatment. Ongoing modeling that accounts for dosing decreases, delays, and discontinuations will further characterize the contribution of paclitaxel pharmacokinetics to PIPN development and enable identification of genetic and metabolomic biomarkers that predict which patients experienced more severe PIPN than would be anticipated based on their paclitaxel PK.

Citation Format: Hertz DL, Kidwell KM, Vangipuram K, Sun D, Henry NL. Association of systemic paclitaxel concentrations with severity and progression of paclitaxel-induced peripheral neuropathy [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 P6-11-03.

CYP2D6 genotype is not associated with survival in breast cancer patients treated with tamoxifen: results from a population-based study

PURPOSE

A number of studies have tested the hypothesis that breast cancer patients with low-activity CYP2D6 genotypes achieve inferior benefit from tamoxifen treatment, putatively due to lack of metabolic activation to endoxifen. Studies have provided conflicting data, and meta-analyses suggest a small but significant increase in cancer recurrence, necessitating additional studies to allow for accurate effect assessment. We conducted a retrospective pharmacogenomic analysis of a prospectively collected community-based cohort of patients with estrogen receptor-positive breast cancer to test for associations between low-activity CYP2D6 genotype and disease outcome in 500 patients treated with adjuvant tamoxifen monotherapy and 500 who did not receive any systemic adjuvant therapy.

METHODS

Tumor-derived DNA was genotyped for common, functionally consequential CYP2D6 polymorphisms (*2, *3, *4, *6, *10, *41, and copy number variants) and assigned a CYP2D6 activity score (AS) ranging from none (0) to full (2). Patients with poor metabolizer (AS = 0) phenotype were compared to patients with AS > 0 and in secondary analyses AS was analyzed quantitatively. Clinical outcome of interest was recurrence free survival (RFS) and analyses using long-rank test were adjusted for relevant clinical covariates (nodal status, tumor size, etc.).

RESULTS

CYP2D6 AS was not associated with RFS in tamoxifen treated patients in univariate analyses (p > 0.2). In adjusted analyses, increasing AS was associated with inferior RFS (Hazard ratio 1.43, 95% confidence interval 1.00-2.04, p = 0.05). In patients that did not receive tamoxifen treatment, increasing CYP2D6 AS, and AS > 0, were associated with superior RFS (each p = 0.0015).

CONCLUSIONS

This population-based study does not support the hypothesis that patients with diminished CYP2D6 activity achieve inferior tamoxifen benefit. These contradictory findings suggest that the association between CYP2D6 genotype and tamoxifen treatment efficacy is null or near null, and unlikely to be useful in clinical practice.

Elevated S100A8 protein expression in breast cancer cells and breast tumor stroma is prognostic of poor disease outcome

PURPOSE

Elevated S100A8 expression has been observed in cancers of the bladder, esophagus, colon, ovary, and breast. S100A8 is expressed by breast cancer cells as well as by infiltrating immune and myeloid cells. Here we investigate the association of elevated S100A8 protein expression in breast cancer cells and in breast tumor stroma with survival outcomes in a cohort of breast cancer patients.

PATIENTS AND METHODS

Tissue microarrays (TMA) were constructed from breast cancer specimens from 417 patients with stage I-III breast cancer treated at the University of Michigan Comprehensive Cancer Center between 2004 and 2006. Representative regions of non-necrotic tumor and distant normal tissue from each patient were used to construct the TMA. Automated quantitative immunofluorescence (AQUA) was used to measure S100A8 protein expression, and samples were scored for breast cancer cell and stromal S100A8 expression. S100A8 staining intensity was assessed as a continuous value and by exploratory dichotomous cutoffs. Associations between breast cancer cell and stromal S100A8 expression with disease-free survival and overall survival were determined using the Kaplan-Meier method and Cox proportional hazard models.

RESULTS

High breast cancer cell S100A8 protein expression (as indicated by AQUA scores), as a continuous measure, was a significant prognostic factor for OS [univariable hazard ratio (HR) 1.24, 95% confidence interval (CI) 1.00-1.55, p = 0.05] in this patient cohort. Exploratory analyses identified optimal S100A8 AQUA score cutoffs within the breast cancer cell and stromal compartments that significantly separated survival curves for the complete cohort. Elevated breast cancer cell and stromal S100A8 expression, indicated by higher S100A8 AQUA scores, significantly associates with poorer breast cancer outcomes, regardless of estrogen receptor status.

CONCLUSIONS

Elevated breast cancer cell and stromal S1008 protein expression are significant indicators of poorer outcomes in early stage breast cancer patients. Evaluation of S100A8 protein expression may provide additional prognostic information beyond traditional breast cancer prognostic biomarkers.

Statistical controversies in clinical research: building the bridge to phase II-efficacy estimation in dose-expansion cohorts

BACKGROUND

Regulatory agencies and others have expressed concern about the uncritical use of dose expansion cohorts (DECs) in phase I oncology trials. Nonetheless, by several metrics-prevalence, size, and number-their popularity is increasing. Although early efficacy estimation in defined populations is a common primary endpoint of DECs, the types of designs best equipped to identify efficacy signals have not been established.

METHODS

We conducted a simulation study of six phase I design templates with multiple DECs: three dose-assignment/adjustment mechanisms multiplied by two analytic approaches for estimating efficacy after the trial is complete. We also investigated the effect of sample size and interim futility analysis on trial performance. Identifying populations in which the treatment is efficacious (true positives) and weeding out inefficacious treatment/populations (true negatives) are competing goals in these trials. Thus, we estimated true and false positive rates for each design.

RESULTS

Adaptively updating the MTD during the DEC improved true positive rates by 8-43% compared with fixing the dose during the DEC phase while maintaining false positive rates. Inclusion of an interim futility analysis decreased the number of patients treated under inefficacious DECs without hurting performance.

CONCLUSION

A substantial gain in efficiency is obtainable using a design template that statistically models toxicity and efficacy against dose level during expansion. Design choices for dose expansion should be motivated by and based upon expected performance. Similar to the common practice in single-arm phase II trials, cohort sample sizes should be justified with respect to their primary aim and include interim analyses to allow for early stopping.

Abstract P6-09-11: Genetic variation in CYP3A affects steady-state exemestane concentrations but does not explain inter-race difference

Background: Exemestane is a third generation steroidal aromatase inhibitor (AI) used for the treatment of estrogen receptor (ER) positive breast cancer in postmenopausal women. Differences in AI treatment efficacy and side effects may be due, in part, to variability in drug exposure. We previously reported that patients who self-report as white and those who carry the low-activity CYP3A4*22 single nucleotide polymorphism (SNP) have increased exemestane steady-state concentrations. Additional SNPs in CYP3A may contribute to pharmacokinetic variability and explain this inter-race difference. CYP3A5*3 (rs776746) is a non-expresser genotype that is far more common in European (minor allele frequency (MAF)∼0.94) than African (MAF∼0.18) individuals. CYP3A7*1C (rs45446698) is believed to tag adult expression of the fetal CYP3A7 enzyme and is relatively uncommon in tested cohorts (European MAF=0.04, African MAF<0.01). The objective of this secondary analysis was to determine whether these additional CYP3A SNPs contribute to variability in steady state exemestane concentrations and explain the inter-race difference.

Methods: 500 patients were randomly assigned to either drug on the Exemestane and Letrozole Pharmacogenetics (ELPh) Study. Clinical data and DNA were collected at baseline and blood samples were collected after 1 or 3 months of treatment to measure steady-state exemestane concentration via HPLC/MS. Genotyping for CYP3A5*3 and CYP3A7*1C was performed via Taqman Allelic Discrimination. Pharmacogenetic association with log-transformed concentrations were tested for each variant by inclusion in a multivariable model with CYP3A4*22 and self-reported race, assuming additive genetic effect, using Tobit regression to censor concentrations below the lower limit of quantification. SNPs with suggestive p-values <0.10 were included in a multivariable model with relevant covariates (AST or ALT>40, body mass index (BMI), and prior chemotherapy) to assess their independent contribution.

Results: In 231 evaluable patients there was a suggestive trend toward lower steady-state exemestane concentrations for CYP3A7*1C carriers (6.3 vs. 8.0 ng/mL) in the model including CYP3A4*22 and race (p=0.083). In the final multivariable model each CYP3A7*1C allele decreased exemestane concentration 31.5% (p=0.035, Table 1). CYP3A5*3 was not associated with exemestane concentration (p>0.2).

Multivariable Model of Exemestane Concentration % change in concentration (95% CI)p-valueCYP3A4*22 (rs35599367)64.5% (23%, 120%)0.0008CYP3A7*1C (rs45446698)-31.5% (-52%, -2.6%)0.035Self-Reported White47.2% (9.0%, 99%)0.012AST or ALT>4041.3% (1.0%, 98%)0.044BMI-0.9% (-2.4%, 0.55%)0.22Prior Chemotherapy-23.5% (-37%, -7.6%)0.006CI: Confidence Interval

Conclusions: Patients with breast cancer who carry CYP3A7*1C have lower steady-state exemestane concentrations but this association does not explain the greater concentrations in self-reported white patients. Ongoing analyses will determine whether exemestane concentration predicts treatment efficacy or toxicity, and if so, whether genetic and clinical factors can be useful for individualizing dosing to optimize outcomes. CYP3A7*1C should be prioritized for analyses of pharmacokinetic variability of other CYP3A substrates.

Citation Format: Hertz DL, Kidwell KM, Gersch CL, Desta Z, Storniolo AM, Stearns V, Skaar TC, Hayes DF, Henry NL, Rae JM. Genetic variation in CYP3A affects steady-state exemestane concentrations but does not explain inter-race difference [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-09-11.

Abstract P5-12-05: CYP3A4*22 polymorphism is associated with increased exemestane concentrations in postmenopausal breast cancer patients

Background: Exemestane is a second generation steroidal aromatase inhibitor (AI) used for the treatment of estrogen receptor (ER) positive breast cancer in postmenopausal women. Variability in AI treatment efficacy and side effects seen across patients may be due, in part, to inter-patient differences in drug exposure. This exposure variability is likely caused by patient genetics factors, such as single nucleotide polymorphisms (SNPs) in drug metabolizing enzymes, or clinical factors such as patient body size, organ function, and comorbidities. The objective of this secondary correlative analysis was to identify genetic and clinical characteristics that affect steady state exemestane concentration, with a specific focus on the influence of inherited genetic variants and baseline hepatic function.

Methods: 500 patients were enrolled on the Exemestane and Letrozole Pharmacogenetics (ELPh) Study and randomized to either drug. Clinical data and DNA were collected at baseline and blood samples were collected after 1 or 3 months of treatment to measure steady-state exemestane concentration via HPLC/MS. Genotyping was performed on a custom Sequenom MassARRAY iPLEX that included the recently discovered low activity CYP3A4*22 (rs35599367) SNP and several other SNPs with putative functional consequence in enzymes thought to be involved in exemestane metabolism (CYP1A1/2, CYP1B1, CYP3A4, CYP4A11, AKR1C3/4, AKR7A2). Our primary hypothesis was that patients carrying CYP3A4*22 variants would have higher serum exemestane concentrations. Other SNPs and clinical characteristics (hepatic and renal function, age, body mass index (BMI), time of sample collection, prior chemotherapy) were assessed for independent association, and then adjusted for in a multivariable tobit regression model for CYP3A4*22 on log-transformed censored exemestane concentration.

Results: 246 (225 randomized to exemestane arm, 21 crossed-over from letrozole arm) patients had exemestane steady state levels and were evaluable in this analysis. As hypothesized, the CYP3A4*22 polymorphism (minor allele frequency=0.06) was associated with a 54% increase in exemestane concentration (95% CI: 14% - 109%, p<0.01). Exemestane concentration was 44% greater in patients who had evidence of hepatic impairment (AST or ALT>40) at baseline (95% CI: 2% - 104%, p=0.02), 1% lower per unit increase in BMI (95% CI: 0% - 3%, p=0.05), and 20% lower in patients who received prior chemotherapy (95% CI: 4% - 34%, p=0.03). Age, renal impairment, and other SNPs were not associated with exemestane concentration. After adjustment for significant clinical covariates the CYP3A4*22 SNP remained significant (p<0.01).

Conclusions: Genetic and clinical predictors of exemestane concentration were discovered in a large cohort of prospectively enrolled estrogen responsive breast cancer patients. Ongoing analyses will determine whether the variability in exemestane concentration was associated with downstream effects on estrogen depletion or treatment-related toxicity. If so, these genetic and clinical characteristics could be useful for individualizing dosing of exemestane to ensure that all patients are receiving maximal benefit with minimal toxicity.

Citation Format: Hertz DL, Kidwell KM, Seewald NJ, Gersch CL, Desta Z, Flockhart DA, Storniolo AM, Stearns V, Skaar TC, Hayes DF, Henry NL, Rae JM. CYP3A4*22 polymorphism is associated with increased exemestane concentrations in postmenopausal breast cancer patients. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P5-12-05.

Abstract P5-02-03: Incidental radiographic findings at the time of breast cancer diagnosis

Background: Perioperative staging imaging to evaluate for distant metastases is frequently performed in patients with newly diagnosed breast cancer, despite clinical guidelines recommending against their routine use in stage I and II disease. In addition, recent technological advances in imaging have led to increased sensitivity for findings, many of which are unrelated to breast cancer. We assessed whether the presence of incidental findings on staging imaging is associated with a higher risk of breast cancer recurrence.

Patients and Methods: A retrospective review of staging imaging for distant metastases was performed in 340 patients with stage II or III invasive breast cancer diagnosed in 2008-2009 at a large academic medical center. Data related to patient demographics, pathology, treatment, and recurrence were abstracted from the electronic medical record. Kaplan Meier curves and Cox proportional hazards models were used to assess the association between the presence of incidental findings and time to disease recurrence.

Results: A total of 169 of 340 patients (49.7%) underwent staging evaluation for distant metastases (CT chest, CT abdomen/pelvis, bone scan, and/or PET-CT). Of these, 146 (86.4%) had at least one suspicious or indeterminate radiographic finding. To clarify these findings, 73 (43.2%) patients underwent follow-up imaging or procedures. Nineteen patients were diagnosed with metastatic disease, 18 of whom were initially thought to have stage III disease and one was thought to have stage II disease. In the 127 patients without definite evidence of metastatic disease who underwent staging imaging, 32 were diagnosed with disease recurrence. With median follow-up of 4.9 years, the presence of indeterminate or suspicious findings at diagnosis was not associated with a significant difference in time to disease recurrence, adjusted for stage, hormone receptor status, and HER2 status (HR 1.44, 95% CI 0.51-6.03, p=0.55).

Time to Disease Recurrence by Imaging ModalityImaging Modality# With Indeterminate or Suspicious Finding(s)# Without Indeterminate or Suspicious Finding(s)Hazard Ratio95% Confidence Intervalp-valueAll Patients without mets at diagnosis127231.440.51-6.030.55CT Chest83521.890.80-4.460.15CT Abdomen/Pelvis91451.380.63-3.040.43Bone Scan351231.040.44-2.460.93

Time to Disease Recurrence by Type of Radiographic AbnormalityType of Abnormal Finding# With Indeterminate or Suspicious Finding(s)# Without Indeterminate or Suspicious Finding(s)Hazard Ratio95% Confidence Intervalp-valuePulmonary nodules70661.650.76-3.580.20Liver lesions46911.720.83-3.600.15Borderline or enlarged lymph nodes201190.570.17-1.960.37

Conclusions: Staging imaging for distant metastases frequently reveals indeterminate findings, whose presence was not associated with a significant risk of disease recurrence in this analysis. Due to low yield for the diagnosis of metastases, staging imaging should not routinely be performed in stage II breast cancer patients.

Citation Format: Brothers JM, Kidwell KM, Brown RK, Henry NL. Incidental radiographic findings at the time of breast cancer diagnosis. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P5-02-03.

Abstract P6-09-02: Analysis of the International tamoxifen pharmacogenomics consortium (ITPC) dataset shows that genotyping DNA derived from tumor does not introduce CYP2D6 genotyping error or mask an association with tamoxifen efficacy

Background: The anti-estrogen tamoxifen is metabolized into the more potent anti-estrogen, endoxifen, primarily by polymorphic CYP2D6. An association between CYP2D6 genotype and tamoxifen efficacy was assessed in a meta-analysis of 4,973 breast cancer patients by the ITPC. A subgroup analysis in 1,996 estrogen receptor (ER)-positive postmenopausal patients receiving 20[thinsp]mg/day tamoxifen for 5 years (criterion 1) found CYP2D6 poor metabolizer genotype was associated with worse invasive disease free survival (IDFS; hazard ratio (HR) 1.25, 95% confidence interval (CI) 1.06-1.47, P=0.009). This meta-analysis did not include data from two prospective trials (Anastrozole, Tamoxifen, Alone or In Combination (ATAC) and Breast Intergroup (BIG) 1-98) both of which meet the patient criteria but failed to replicate the ITPC findings. Some ITPC investigators criticized ATAC and BIG 1-98 for genotyping CYP2D6 from tumor-derived DNA, positing this leads to genotyping errors detected by Hardy-Weinberg Equilibrium (HWE). However, ITPC analyses did not exclude tumor-derived CYP2D6 genotypes or report HWE. Therefore, we re-analyzed the ITPC data to investigate claims that tumor-derived genotyping causes HWE departure and masks the association between CYP2D6 genotype and tamoxifen efficacy.

Methods: The ITPC dataset was filtered to patients fulfilling criterion 1. HWE for CYP2D6*4 was analyzed in Caucasian patients (n=1,619) by study, by DNA source (tumor or blood), and in the entire subgroup. The ITPC meta-analysis was rerun stratified by DNA source using the same specifications (patients, phenotype, genotype, statistical model, etc.) as in ITPC.

Results: Significant HWE deviation for CYP2D6*4, the most common variant (MAF =0.2), was not observed in any study genotyped from tumor but was observed in one study genotyped from blood. Combining studies led to significant HWE deviations in studies genotyped from both blood and tumor, and for the entire subcohort (Table 1). Associations between CYP2D6 genotype and IDFS stratified by DNA source yielded similar, non-statistically significant, results (blood: n=933, HR=1.19, 95% CI 0.91-1.57, P=0.21; tumor: n=997, HR=1.19, 95% CI 0.99-1.44, P=0.07).

Conclusions: HWE deviations for CYP2D6*4 are not uniformly or exclusively found in studies using tumor DNA, but can occur as a statistical consequence of combining genotypes from heterogeneous populations like in the multi-institution BIG 1-98 and ATAC studies. Re-analysis of the ITPC dataset stratified by DNA source refutes the hypothesis that genotyping tumor DNA masks a pharmacogenetic association. These findings reaffirm the validity of the BIG 1-98 and ATAC analyses and support inclusion of these studies in the ITPC meta-analysis to rigorously assess the association between CYP2D6 genotype and tamoxifen efficacy.

CYP2D6*4 HWE Test in Caucasian Patients from Each ITPC Study, by DNA Source, and CombinedDNA SourceStudy NumberNHWEBlood2700.68 4530.03 6130.28 84640.12 930.56 102220.0002 Total8250.0004Tumor51970.41 62170.04 83800.04 Total7940.0037CombinedTotal16190.000006

Citation Format: Kidwell KM, Hertz DL, Leyland-Jones B, Regan MM, Dowsett M, Rae JM. Analysis of the International tamoxifen pharmacogenomics consortium (ITPC) dataset shows that genotyping DNA derived from tumor does not introduce CYP2D6 genotyping error or mask an association with tamoxifen efficacy. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-09-02.

Abstract P3-05-01: Molecular analysis of cancer tissue, circulating tumor cells (CTC) and cell-free plasma tumor DNA (ptDNA) suggests variable mechanisms of resistance to endocrine therapy (ET) in estrogen receptor (ER) positive metastatic breast cancer (MBC)

Introduction: Fifty percent of ER positive MBC patients do not benefit from ET. Potential mechanisms of resistance to ET in this patient population include absence of ER expression by deletion or suppression, alteration in ER signaling pathway genes, or upregulation of multiple growth factor receptor pathways. We hypothesized that genotyping and phenotyping of CTC combined with genomic analysis of ptDNA will provide important insights into the multiple mechanisms of ET resistance and that a set of blood tests might serve as a "liquid biopsy" abrogating the need for tissue specimens.

Methods: Twenty-four patients providing informed consent were enrolled into the Mi CTC-ONCOSEQ study, a companion trial to Mi-ONCOSEQ (the Michigan Oncology Sequencing Program). Seven of these patients (5 with ER immunohistochemistry (IHC) positive and 2 with ER negative cancers) who had available archived primary and metastatic cancer tissue, a research metastatic biopsy for genomic analysis, and who had ≥5CTC/7.5 ml whole blood (WB) characterized for ER protein (CTC-ER) are the focus of this report. All the patients were ET refractory. None of them was progressing on fulvestrant at the time of study entry. CTC enumeration and phenotyping was performed with CellSearch©. Circulating ptDNA was analyzed by droplet digital polymerase chain reaction (ddPCR). ER status from archived tissue was obtained from chart review. ER mRNA expression was determined in the research biopsy of metastatic tissue by using quantitative RNA sequencing. Mutational status of ER gene, ESR1, was determined by Next-gen Sequencing using the Illumina HiSeq 2500 platform.

Results: The 2 control patients with triple negative breast cancer had negative CTC-ER. Discordance between CTC-ER and tissue ER by IHC was observed (Table). Two of the 5 ER positive patients retained CTC-ER positivity (39% and 19% of the CTC). One of them (#7) harbored an ESR1 mutation in the research biopsy tissue and in ptDNA, whereas the other (#14) had wild type (WT) ESR1. CTC-ER protein levels in patients #12, 17 and 24 were negative. All had WT ESR1 in the research biopsy tissue. Of note, patient #12 had WT ESR1 in the research biopsy, but an ESR1 mutation was detected in her ptDNA.

Pt#CTC-ER Tissue-ER  ESR1 status in research biopsyESR1 status in ptDNA N[deg]CTC/7.5ml WB% CTC-ER +Primary by IHCMet by IHCMet research biopsy by mRNA  71839%+++Y537SY537S141619%+NA+WTWT12130%+++WTD538G17160%++weakly+WTWT242750%+weakly+weakly+WTWT

Conclusions: These exploratory data suggest heterogeneous mechanisms of resistance to ET in patients with previously determined ER-positive MBC, including ESR1 mutations in ER positive cases (seen in 2 patients) and loss of ER expression (seen in CTC of 3 patients). In contrast, other cancers continue to express WT ESR1, and therefore must have developed alternative mechanisms of resistance. At least 2 of these mechanisms can be detected and monitored with complementary circulating assays: CTC and ptDNA. Further investigations are needed to understand the heterogeneous mechanisms of resistance to ET.

Citation Format: Paoletti C, Aung K, Cannell EM, Darga EP, Chu D, Kidwell KM, Thomas DG, Tokudome N, Brown ME, McNutt LM, Gersch C, Schott AF, Park BH, Robinson DR, Chinnaiyan AM, Rae JM, Hayes DF. Molecular analysis of cancer tissue, circulating tumor cells (CTC) and cell-free plasma tumor DNA (ptDNA) suggests variable mechanisms of resistance to endocrine therapy (ET) in estrogen receptor (ER) positive metastatic breast cancer (MBC). [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-05-01.

Abstract P1-04-01: Significance of circulating tumor cells in metastatic triple negative breast cancer: Results of an open label, randomized, phase II trial of nanoparticle albumin-bound paclitaxel with or without the anti-death receptor 5 tigatuzumab (TBCRC 019)

Background: Circulating Tumor cells (CTCs) are prognostic at baseline and first follow-up in patients with metastatic breast cancer (MBC). Using the most commonly used assay (CellSearch®), we have previously reported the ability to detect apoptotic vs. non-apoptotic CTCs in patients with MBC. However, there has been concern regarding the performance of the CellSearch® assay in patients with triple negative (TN) MBC. We hypothesized that CellSearch® is an effective assay in patients with TN MBC, and that CTC-apoptosis might further separate prognosis. Therefore, we studied CTCs in patients with TN MBC who participated in a prospective randomized phase II trial testing for activity of tigatuzumab (TIG) in combination with nanoparticle albumin-bound paclitaxel (nab-PAC) conducted by the Translational Breast Cancer Research Consortium (overall results reported by Forero A., et al, ASCO 2013).

Methods: Whole blood (WB) was drawn into a CellSave tube at baseline, day 15, and day 29 and CTC counts were determined using the CXC CellSearch® kit. Apoptosis was characterized by staining with a monoclonal antibody that detects a neo-epitope on fragmented cytokeratin (M-30) and independently by visual inspection (nucleic condensation and/or fragmentation, as well as granular cytokeratin). Association between levels of CTCs and CTC-apoptosis with the overall response rate (ORR) and progression free survival (PFS) at baseline, day 15, and day 29 was assessed using logistic regression, Kaplan Meier curves, and Cox proportional hazards modeling.

Results: Of the 60 patients entered into the trial, 52 were evaluable for CTCs. Of these, 19/52 (36.5%), 14/52 (26.9%), and 13/49 (26.5%) had elevated CTCs (≥5CTC/7.5 ml WB) at baseline, day 15, and day 29, respectively. Patients with elevated CTCs at each time point had worse PFS than patients with low or no CTCs. Hazard rates (HR) at baseline, day 15, and day 29 were 2.38 (95% CI: 1.27-4.45, p = 0.007), 2.87 (95% CI: 1.46-5.66, p = 0.002), and 3.40 (95% CI: 1.68-6.89, p = 0.001), respectively. The odds of overall response for those who had elevated CTCs compared to those who did not at baseline, day 15, and day 29, were 0.25 (95% CI: 0.073-0.81, p = 0.024), 0.18 (95% CI: 0.04-0.67, p = 0.014), and 0.06 (95% CI: 0.01-0.28, p = 0.001), respectively. There was no apparent prognostic effect comparing the degree of CTC-apoptosis vs. non-apoptosis.

Conclusions: Similar to observations in other intrinsic subgroups, CTCs were detected in a large fraction of TN MBC patients at baseline using CellSearch® assay, and reductions in CTC levels reflected response. In these homogenously prospectively enrolled TN MBC patients, regardless of treatment, CTCs are prognostic at baseline, day 15, and day 29. It does not appear that analysis of CTC-apoptosis is prognostic.

Supported by Susan G. Komen for the Cure, Veridex, LLC, Fashion Footwear Charitable Foundation of New York/QVC Presents Shoes on Sale™ (DFH), Associazione Sandro Pitigliani and by a studentship from FIRC (CP), Triple Negative Breast Cancer Foundation, The AVON Foundation, and The Breast Cancer Research Foundation.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-04-01.

P3-13-01: Boost Radiation Therapy Not of Value in Reducing IBTR of Invasive or Noninvasive Breast Cancers for Patients with DCIS: Results from the NSABP B-24 Trial

Background: Whole breast irradiation therapy following lumpectomy for invasive breast cancer (IBC) or noninvasive breast cancer (DCIS) significantly reduces the risk of local recurrence. Boost radiation therapy to the tumor bed has been proven to additionally lower the risk of recurrence for IBC. The benefit of boost therapy in patients with DCIS is less certain. We carried out a review of the NSABP B-24 trial to assess the benefit of boost therapy.

Methods: After lumpectomy and radiation therapy, 1804 women with DCIS were randomly assigned to placebo (902) or tamoxifen (902). Whole breast irradiation therapy (50 Gy) was mandatory. Boost radiation therapy was optional, and boost status was known for 1,569 patients. Of these, 1392 patients (86.97%) were identified as having all data sufficient for multivariate analysis. Of these, 613 received boost therapy ranging from 1 Gy −20 Gy, with 81.5% receiving 10 Gy. Mean time of follow-up was 161 months.

Results: Patients who received boost radiation therapy were more likely to be younger (p=0.04), have positive margins (p=0.007), and be more likely to have comedo necrosis (p=0.03). Multivariate analysis identified only treatment (tamoxifen vs placebo) (HR=0.74, 95% CI=0.57−0.98, p=0.034), age (≥ 50 verses < 50) (HR=0.47, 95% CI=0.36−0.61, p<0.0001), and margin status (positive vs negative) (HR: 1.79, 95% CI= 1.31−2.43, p<0.001) as significant predictors for ipsilateral breast tumor recurrence (IBTR). Boost had no significant effect on IBTR (HR=0.87, 95% CI=0.66−1.15, p=0.33). The lack of boost effect applied to both invasive (HR=0.86, 95% CI=0.58−1.27, p=0.44) and noninvasive IBTR (HR=0.89, 95% CI=0.60−1.33, p=0.56).

No interaction was seen between boost and treatment, age, margin status, or comedo necrosis.

Conclusion: In NSABP B-24, the addition of boost radiation therapy was not found to be of value in reducing IBTR of invasive or noninvasive breast cancers for patients with DCIS.

Supported by PHS grants NCI-U10-CA-69651, NCI-U10-CA-12027, and NCI P30-CA-14599 from the US NCI and AstraZeneca.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-13-01.