Application of PET Tracers in Molecular Imaging for Breast Cancer.

PURPOSE OF REVIEW: Molecular imaging with positron emission tomography (PET) is a powerful tool to visualize breast cancer characteristics. Nonetheless, implementation of PET imaging into cancer care is challenging, and essential steps have been outlined in the international "imaging biomarker roadmap." In this review, we identify hurdles and provide recommendations for implementation of PET biomarkers in breast cancer care, focusing on the PET tracers 2-[18F]-fluoro-2-deoxyglucose ([18F]-FDG), sodium [18F]-fluoride ([18F]-NaF), 16α-[18F]-fluoroestradiol ([18F]-FES), and [89Zr]-trastuzumab. RECENT FINDINGS: Technical validity of [18F]-FDG, [18F]-NaF, and [18F]-FES is established and supported by international guidelines. However, support for clinical validity and utility is still pending for these PET tracers in breast cancer, due to variable endpoints and procedures in clinical studies. Assessment of clinical validity and utility is essential towards implementation; however, these steps are still lacking for PET biomarkers in breast cancer. This could be solved by adding PET biomarkers to randomized trials, development of imaging data warehouses, and harmonization of endpoints and procedures.

Paclitaxel plus Eftilagimod Alpha, a Soluble LAG-3 Protein, in Metastatic, HR+ Breast Cancer: Results from AIPAC, a Randomized, Placebo Controlled Phase IIb Trial.

PURPOSE: Eftilagimod alpha (efti), a soluble lymphocyte activation gene (LAG-3) protein and MHC class II agonist, enhances innate and adaptive immunity. Active Immunotherapy PAClitaxel (AIPAC) evaluated safety and efficacy of efti plus paclitaxel in patients with predominantly endocrine-resistant, hormone receptor-positive, HER2-negative metastatic breast cancer (ET-resistant HR+ HER2- MBC). PATIENTS AND METHODS: Women with HR+ HER2- MBC were randomized 1:1 to weekly intravenous paclitaxel (80 mg/m2) and subcutaneous efti (30 mg) or placebo every 2 weeks for six 4-week cycles, then monthly subcutaneous efti (30 mg) or placebo maintenance. Primary endpoint was progression-free survival (PFS) by blinded independent central review. Secondary endpoints included overall survival (OS), safety/tolerability, pharmacokinetics/pharmacodynamics, and quality of life. Exploratory endpoints included cellular biomarkers. RESULTS: 114 patients received efti and 112 patients received placebo. Median age was 60 years (91.6% visceral disease, 84.1% ET-resistant, 44.2% with previous CDK4/6 inhibitor treatment). Median PFS at 7.3 months was similar for efti and placebo. Median OS was not significantly improved for efti (20.4 vs. 17.5 months; HR, 0.88; P = 0.197) but became significant for predefined exploratory subgroups. EORTC QLQC30-B23 global health status was sustained for efti but deteriorated for placebo. Efti increased absolute lymphocyte, monocyte and secondary target cell (CD4, CD8) counts, plasma IFNγ and CXCL10 levels. CONCLUSIONS: Although the primary endpoint, PFS, was not met, AIPAC confirmed expected pharmacodynamic effects and demonstrated excellent safety profile for efti. OS was not significantly improved globally (2.9-month difference), but was significantly improved in exploratory biomarker subgroups, warranting further studies to clarify efti's role in patients with ET-resistant HER2- MBC.

Correlation between Histopathological Prognostic Tumor Characteristics and [18F]FDG Uptake in Corresponding Metastases in Newly Diagnosed Metastatic Breast Cancer.

BACKGROUND: In metastatic breast cancer (MBC), [18F]fluorodeoxyglucose positron emission tomography/computed tomography ([18F]FDG-PET/CT) can be used for staging. We evaluated the correlation between BC histopathological characteristics and [18F]FDG uptake in corresponding metastases. PATIENTS AND METHODS: Patients with non-rapidly progressive MBC of all subtypes prospectively underwent a baseline histological metastasis biopsy and [18F]FDG-PET. Biopsies were assessed for estrogen, progesterone, and human epidermal growth factor receptor 2 (ER, PR, HER2); Ki-67; and histological subtype. [18F]FDG uptake was expressed as maximum standardized uptake value (SUVmax) and results were expressed as geometric means. RESULTS: Of 200 patients, 188 had evaluable metastasis biopsies, and 182 of these contained tumor. HER2 positivity and Ki-67 ≥ 20% were correlated with higher [18F]FDG uptake (estimated geometric mean SUVmax 10.0 and 8.8, respectively; p = 0.0064 and p = 0.014). [18F]FDG uptake was lowest in ER-positive/HER2-negative BC and highest in HER2-positive BC (geometric mean SUVmax 6.8 and 10.0, respectively; p = 0.0058). Although [18F]FDG uptake was lower in invasive lobular carcinoma (n = 31) than invasive carcinoma NST (n = 146) (estimated geometric mean SUVmax 5.8 versus 7.8; p = 0.014), the metastasis detection rate was similar. CONCLUSIONS: [18F]FDG-PET is a powerful tool to detect metastases, including invasive lobular carcinoma. Although BC histopathological characteristics are related to [18F]FDG uptake, [18F]FDG-PET and biopsy remain complementary in MBC staging (NCT01957332).

Molecular imaging as biomarker for treatment response and outcome in breast cancer.

Molecular imaging, such as positron emission tomography (PET), is increasingly used as biomarker to predict and assess treatment response in breast cancer. The number of biomarkers is expanding with specific tracers for tumour characteristics throughout the body and this information can be used to aid the decision-making process. These measurements include metabolic activity using [18F]fluorodeoxyglucose PET ([18F]FDG-PET), oestrogen receptor (ER) expression using 16α-[18F]Fluoro-17ß-oestradiol ([18F]FES)-PET and human epidermal growth factor receptor 2 (HER2) expression using PET with radiolabelled trastuzumab (HER2-PET). In early breast cancer, baseline [18F]FDG-PET is frequently used for staging, but limited subtype-specific data reduce its usefulness as biomarker for treatment response or outcome. Early metabolic change on serial [18F]FDG-PET is increasingly used in the neo-adjuvant setting as dynamic biomarker to predict pathological complete response to systemic therapy, potentially allowing de-intensification or step-up intensification of treatment. In the metastatic setting, baseline [18F]FDG-PET and [18F]FES-PET can be used as biomarker to predict treatment response, in triple-negative and ER-positive breast cancer, respectively. Metabolic progression on repeated [18F]FDG-PET appears to precede progressive disease on standard evaluation imaging; however, subtype-specific studies are limited and more prospective data are needed before implementation in clinical practice. Even though (repeated) [18F]FDG-PET, [18F]FES-PET and HER2-PEt all show promising results as biomarkers to predict therapy response and outcome, for eventual integration into clinical practice, future studies will have to clarify at what timepoint this integration has to optimally take place.

Lapatinib and 17AAG reduce 89Zr-trastuzumab-F(ab')2 uptake in SKBR3 tumor xenografts.

Human epidermal growth factor receptor-2 (HER2) directed therapy potentially can be improved by insight in drug effects on HER2 expression. This study evaluates the effects of the EGFR/HER2 tyrosine kinase inhibitor lapatinib, the heat shock protein-90 inhibitor 17AAG, and their combination, on HER2 expression with in vivo HER2-PET imaging. Lapatinib and 17AAG effects on EGFR and HER2 membrane expression were determined in vitro using flow cytometry of human SKBR3 tumor cells. Effect of lapatinib on HER2 internalization was studied in vitro by (89)Zr-trastuzumab-F(ab')(2) internalization. For in vivo evaluation, (89)Zr-trastuzumab-F(ab')(2) µPET imaging was performed two times with a 7 day interval. Lapatinib was administered for 6 days, starting 1 day after the baseline scan. 17AAG was given 1 day before the second (89)Zr-trastuzumab-F(ab')(2) injection. Imaging data were compared with ex vivo biodistribution analysis and HER2 immunohistochemical staining. 17AAG treatment lowered EGFR expression by 41% (P = 0.016) and HER2 by 76% (P = 0.022). EGFR/HER2 downregulation by 17AAG was inhibited by lapatinib pretreatment. Lapatinib reduced internalization of (89)Zr-trastuzumab-F(ab')(2) with 25% (P = 0.0022). (89)Zr-trastuzumab-F(ab')(2) tumor to blood ratio was lowered 32% by lapatinib (P = 0.00004), 34% by 17AAG (P = 0.0022) and even 53% by the combination (P = 0.011). Lapatinib inhibits HER2 internalization and 17AAG lowers HER2 membrane expression. Both drugs reduce (89)Zr-trastuzumab-F(ab')(2) tumor uptake. Based on our findings, supported by previous preclinical data indicating the antitumor potency of lapatinib in combination with HSP90 inhibition, combination of these drugs deserves further investigation.

Clinical Validity of 16α-[18F]Fluoro-17ß-Estradiol Positron Emission Tomography/Computed Tomography to Assess Estrogen Receptor Status in Newly Diagnosed Metastatic Breast Cancer.

PURPOSE: Determining the estrogen receptor (ER) status is essential in metastatic breast cancer (MBC) management. Whole-body ER imaging with 16α-[18F]fluoro-17ß-estradiol positron emission tomography ([18F]FES-PET) is increasingly used for this purpose. To establish the clinical validity of the [18F]FES-PET, we studied the diagnostic accuracy of qualitative and quantitative [18F]FES-PET assessment to predict ER expression by immunohistochemistry in a metastasis. METHODS: In a prospective multicenter trial, 200 patients with newly diagnosed MBC underwent extensive workup including molecular imaging. For this subanalysis, ER expression in the biopsied metastasis was related to qualitative whole-body [18F]FES-PET evaluation and quantitative [18F]FES uptake in the corresponding metastasis. A review and meta-analysis regarding [18F]FES-PET diagnostic performance were performed. RESULTS: Whole-body [18F]FES-PET assessment predicted ER expression in the biopsied metastasis with good accuracy: a sensitivity of 95% (95% CI, 89 to 97), a specificity of 80% (66 to 89), a positive predictive value (PPV) of 93% (87 to 96), and a negative predictive value (NPV) of 85% (72 to 92) in 181 of 200 evaluable patients. Quantitative [18F]FES uptake predicted ER immunohistochemistry in the corresponding metastasis with a sensitivity/specificity of 91%/69% and a PPV/NPV of 90%/71% in 156 of 200 evaluable patients. For bone metastases, PPV/NPV was 92%/81%. Meta-analysis with addition of our data has increased diagnostic performance and narrowed the 95% CIs compared with previous studies with a sensitivity/specificity of both 86% (81 to 90 and 73 to 93, respectively). CONCLUSION: In this largest prospective series so far, we established the clinical validity of [18F]FES-PET to determine tumor ER status in MBC. In view of the high diagnostic accuracy of qualitatively assessed whole-body [18F]FES-PET, this noninvasive imaging modality can be considered a valid alternative to a biopsy of a metastasis to determine ER status in newly MBC (ClinicalTrials.gov identifier: NCT01957332).

Detection of Dural Metastases Before the Onset of Clinical Symptoms by 16α-[18F]Fluoro-17ß-Estradiol PET in a Patient With Estrogen Receptor-Positive Breast Cancer.

ABSTRACT: We offer an illustrative case about estrogen receptor (ER) imaging (also known as 16α-[18F]fluoro-17ß-estradiol ([18F]-FES) PET) and the detection of metastatic lesions in the dural region. We present a case of a woman with ER-positive metastatic breast cancer and high [18F]-FES uptake in the dural region on PET imaging, without associated clinical symptoms. These lesions were missed on [18F]-FDG PET because of physiological [18F]-FDG uptake in the brain. This case highlighted some difficulties in the interpretation of imaging of brain metastases and demonstrated the added value of [18F]-FES PET imaging. [18F]-FES PET could be used to prove the presence of ER-positive metastases in the brain.

Serial [18F]-FDHT-PET to predict bicalutamide efficacy in patients with androgen receptor positive metastatic breast cancer.

BACKGROUND: The androgen receptor (AR) is a potential target in metastatic breast cancer (MBC), and 16ß-[18F]-fluoro-5α-dihydrotestosterone positron emission tomography ([18F]-FDHT-PET) can be used for noninvasive visualisation of AR. [18F]-FDHT uptake reduction during AR-targeting therapy reflects AR occupancy and might be predictive for treatment response. We assessed the feasibility of [18F]-FDHT-PET to detect changes in AR availability during bicalutamide treatment and correlated these changes with treatment response. PATIENTS AND METHODS: Patients with AR + MBC, regardless of oestrogen receptor status, received an [18F]-FDHT-PET at baseline and after 4-6 weeks bicalutamide treatment. Baseline [18F]-FDHT uptake was expressed as maximum standardised uptake value. Percentage change in tracer uptake, corrected for background activity (SUVcor), between baseline and follow-up PET scan (% reduction), was assessed per-patient and lesion. Clinical benefit was determined in accordance with Response Evaluation Criteria in Solid Tumours (RECIST) 1.1 or clinical evaluation (absence of disease progression for ≥24 weeks). RESULTS: Baseline [18F]-FDHT-PET in 21 patients detected 341 of 515 lesions found with standard imaging and 21 new lesions. Follow-up [18F]-FDHT-PET was evaluable in 17 patients with 349 lesions, showing a decrease in median SUVcor from 1.3 to 0.7 per-patient and lesion (P < 0.001). Median % reduction per-patient was -45% and per-lesion -39%. In patients with progressive disease (n = 11), median % reduction was -30% versus -53% for patients who showed clinical benefit (in accordance with RECIST (n = 3) or clinical evaluation (n = 3); P = 0.338). CONCLUSION: In this feasibility study, a bicalutamide-induced reduction in [18F]-FDHT uptake could be detected by follow-up [18F]-FDHT-PET in patients with AR + MBC. However, this change could not predict bicalutamide response. CLINICAL TRIAL INFORMATION: NCT02697032.

Radiolabeled Monoclonal Antibody Against Colony-Stimulating Factor 1 Receptor Specifically Distributes to the Spleen and Liver in Immunocompetent Mice.

Macrophages can promote tumor development. Preclinically, targeting macrophages by colony-stimulating factor 1 (CSF1)/CSF1 receptor (CSF1R) monoclonal antibodies (mAbs) enhances conventional therapeutics in combination treatments. The physiological distribution and tumor uptake of CSF1R mAbs are unknown. Therefore, we radiolabeled a murine CSF1R mAb and preclinically visualized its biodistribution by PET. CSF1R mAb was conjugated to N-succinyl-desferrioxamine (N-suc-DFO) and subsequently radiolabeled with zirconium-89 (89Zr). Optimal protein antibody dose was first determined in non-tumor-bearing mice to assess physiological distribution. Next, biodistribution of optimal protein dose and 89Zr-labeled isotype control was compared with PET and ex vivo biodistribution after 24 and 72 h in mammary tumor-bearing mice. Tissue autoradiography and immunohistochemistry determined radioactivity distribution and tissue macrophage presence, respectively. [89Zr]Zr-DFO-N-suc-CSF1R-mAb optimal protein dose was 10 mg/kg, with blood pool levels of 10 ± 2% injected dose per gram tissue (ID/g) and spleen and liver uptake of 17 ± 4 and 11 ± 4%ID/g at 72 h. In contrast, 0.4 mg/kg of [89Zr]Zr-DFO-N-suc-CSF1R mAb was eliminated from circulation within 24 h; spleen and liver uptake was 126 ± 44% and 34 ± 7%ID/g, respectively. Tumor-bearing mice showed higher uptake of [89Zr]Zr-DFO-N-suc-CSF1R-mAb in the liver, lymphoid tissues, duodenum, and ileum, but not in the tumor than did 89Zr-labeled control at 72 h. Immunohistochemistry and autoradiography showed that 89Zr was localized to macrophages within lymphoid tissues. Following [89Zr]Zr-DFO-N-suc-CSF1R-mAb administration, tumor macrophages were almost absent, whereas isotype-group tumors contained over 500 cells/mm2. We hypothesize that intratumoral macrophage depletion by [89Zr]Zr-DFO-N-suc-CSF1R-mAb precluded tumor uptake higher than 89Zr-labeled control. Translation of molecular imaging of macrophage-targeting therapeutics to humans may support macrophage-directed therapeutic development.

Value of 18F-FES PET in Solving Clinical Dilemmas in Breast Cancer Patients: A Retrospective Study.

Breast cancer (BC) is a heterogeneous disease in which estrogen receptor (ER) expression plays an important role in most tumors. A clinical dilemma may arise when a metastasis biopsy to determine the ER status cannot be performed safely or when ER heterogeneity is suspected between tumor lesions. Whole-body ER imaging, such as 16α-18F-fluoro-17ß-estradiol (18F-FES) PET, may have added value in these situations. However, the role of this imaging technique in routine clinical practice remains to be further determined. Therefore, we assessed whether the physician's remaining clinical dilemma after the standard workup was solved by the 18F-FES PET scan. Methods: This retrospective study included 18F-FES PET scans of patients who had (or were suspected to have) ER-positive metastatic BC and for whom a clinical dilemma remained after the standard workup. The scans were performed at the University Medical Center of Groningen between November 2009 and January 2019. We investigated whether the physician's clinical dilemma was solved, defined either as solving the clinical dilemma through the 18F-FES PET results or as basing a treatment decision directly on the 18F-FES PET results. In addition, the category of the clinical dilemma was reported, as well as the rate of 18F-FES-positive or -negative PET scans, and any correlation to the frequency of solved dilemmas was determined. Results: One hundred 18F-FES PET scans were performed on 83 patients. The clinical dilemma categories were inability to determine the extent of metastatic disease or suspected metastatic disease with the standard workup (n = 52), unclear ER status of the tumor (n = 31), and inability to determine which primary tumor caused the metastases (n = 17). The dilemmas were solved by 18F-FES PET in 87 of 100 scans (87%). In 81 of 87 scans, a treatment decision was based directly on 18F-FES PET results (treatment change, 51 scans; continuance, 30 scans). The frequency of solved dilemmas was not related to the clinical dilemma category (P = 0.334). However, the frequency of solved dilemmas was related to whether scans were 18F-FES-positive (n = 63) or 18F-FES-negative (n = 37; P < 0.001). Conclusion: For various indications, the 18F-FES PET scan can help to solve most clinical dilemmas that may remain after the standard workup. Therefore, the 18F-FES PET scan has added value in BC patients who present the physician with a clinical dilemma.

Analyzing the Estrogen Receptor Status of Liver Metastases with [18F]-FES-PET in Patients with Breast Cancer.

BACKGROUND: Positron emission tomography (PET) with 16α-[18F]-fluoro-17ß-estradiol ([18F]-FES) can visualize estrogen receptor (ER) expression, but it is challenging to determine the ER status of liver metastases, due to high physiological [18F]-FES uptake. We evaluated whether [18F]-FES-PET can be used to determine the ER status of liver metastases, using corresponding liver biopsies as the gold standard. METHODS: Patients with metastatic breast cancer (n = 23) were included if they had undergone a [18F]-FES-PET, liver metastasis biopsy, CT-scan, and [18F]-FDG-PET. [18F]-FES-PET scans were assessed by visual and quantitative analysis, tracer uptake was correlated with ER expression measured by immunohistochemical staining and the effects of region-of-interest size and background correction were determined. RESULTS: Visual analysis allowed ER assessment of liver metastases with 100% specificity and 18% sensitivity. Quantitative analysis improved the sensitivity. Reduction of the region-of-interest size did not further improve the results, but background correction improved ER assessment, resulting in 83% specificity and 77% sensitivity. Using separate thresholds for ER+ and ER- metastases, positive and negative predictive values of 100% and 75%, respectively, could be obtained, although 30% of metastases remained inconclusive. CONCLUSION: In the majority of liver metastases, ER status can be determined with [18F]-FES-PET if background correction and separate thresholds are applied.

Effects of supervised exercise during adjuvant endocrine therapy in overweight or obese patients with breast cancer: The I-MOVE study.

BACKGROUND: Adjuvant endocrine therapy (ET) in patients with breast cancer (BC) increases the risk of becoming less physically active. Physical inactivity is associated with a higher risk of treatment-related side effects and mortality. This study investigated whether supervised exercise increased the proportion of patients adhering to the national physical activity (PA) guideline during adjuvant ET in overweight or obese BC patients. METHODS: This multicentre single-arm clinical trial included patients with BC participating in a 12-week supervised exercise intervention. An accelerometer measured moderate to vigorous PA (MVPA) at baseline (T0), after 12 (T1) and 26 weeks (T2). The primary endpoint was change in the proportion of patients with weekly ≥150 min of MVPA at T1 compared to T0. Secondary endpoints were adherence to PA guideline at T2, metabolic syndrome (MetS), body composition, health-related quality of life (HRQoL) and BC-specific functioning and symptoms, self-reported PA, self-efficacy, exercise motivation and satisfaction with life. RESULTS: 141 patients with a median age of 61 years and a mean BMI of 31.3 participated. Adherence to the PA guideline increased from 38.3% at T0, to 40.4% at T1 (p = .112) and 44.7% at T2 (p = .003). MetS, body composition, HRQoL, BC-specific functioning and symptoms (i.e. fatigue, dyspnoea), self-reported PA, self-efficacy, exercise motivation and satisfaction with life improved significantly over time. CONCLUSIONS: Supervised exercise increased the proportion of BC patients adhering to the PA guideline over time. Furthermore, MetS, body composition, HRQoL and symptoms improved. Our findings highlight the clinical relevance of supervised exercise during ET in overweight BC patients. CLINICAL TRIAL INFORMATION: (NCT02424292).

Assessment of Bone Lesions with 18F-FDG PET Compared with 99mTc Bone Scintigraphy Leads to Clinically Relevant Differences in Metastatic Breast Cancer Management.

It is unknown whether assessment of potential bone lesions in metastatic breast cancer (MBC) by 18F-FDG PET instead of 99mTc bone scintigraphy (BS) supports clinically relevant changes in MBC management. Therefore, we retrospectively compared management recommendations based on bone lesion assessment by 18F-FDG PET plus contrast-enhanced CT (ceCT) or BS plus ceCT, for patients with newly diagnosed MBC. Methods: Baseline ceCT, BS, and 18F-FDG PET for all patients included in the IMPACT-MBC study (NCT01957332) at the University Medical Center Groningen were reviewed for bone lesions. If bone lesions were found by any imaging modality, virtual MBC management recommendations were made by a multidisciplinary expert panel, based on either 18F-FDG PET plus ceCT or BS plus ceCT. The panel had access to standard clinicopathologic information and baseline imaging findings outside the skeleton. Clinically relevant management differences between the 2 recommendations were defined either as different treatment intent (curative, noncurative, or unable to determine) or as different systemic or local treatment. If no bone lesions were found by any imaging modality, the patients were included in the analyses without expert review. Results: In total, 3,473 unequivocal bone lesions were identified in 102 evaluated patients (39% by ceCT, 26% by BS, and 87% by 18F-FDG PET). Additional bone lesions on 18F-FDG PET plus ceCT compared with BS plus ceCT led to change in MBC management recommendations in 16% of patients (95% CI, 10%-24%). BS also changed management compared with 18F-FDG PET in 1 patient (1%; 95% CI, 0%-5%). In 26% (95% CI, 19%-36%) of patients, an additional 18F-FDG PET exam was requested, because BS provided insufficient information. Conclusion: In this exploratory analysis of newly diagnosed MBC patients, 18F-FDG PET versus BS to assess bone lesions resulted in clinically relevant management differences in 16% of patients. BS delivered insufficient information in over one fourth of patients, resulting in an additional request for 18F-FDG PET. On the basis of these data, 18F-FDG PET should be considered a primary imaging modality for assessment of bone lesions in newly diagnosed MBC.

Image Quality and Interpretation of [18F]-FES-PET: Is There any Effect of Food Intake?

BACKGROUND: High physiological 16α-[18F]-fluoro-17ß-estradiol ([18F]-FES) uptake in the abdomen is a limitation of this positron emission tomography (PET) tracer. Therefore, we investigated the effect of food intake prior to PET acquisition on abdominal background activity in [18F]-FES-PET scans. METHODS: Breast cancer patients referred for [18F]-FES-PET were included. Three groups were designed: (1) patients who consumed a chocolate bar (fatty meal) between tracer injection and imaging (n = 20), (2) patients who fasted before imaging (n = 20), and (3) patients without diet restrictions (control group, n = 20). We compared the physiological [18F]-FES uptake, expressed as mean standardized uptake value (SUVmean), in the abdomen between groups. RESULTS: A significant difference in [18F]-FES uptake in the gall bladder and stomach lumen was observed between groups, with the lowest values for the chocolate group and highest for the fasting group (p = 0.015 and p = 0.011, respectively). Post hoc analysis showed significant differences in the SUVmean of these organs between the chocolate and fasting groups, but not between the chocolate and control groups. CONCLUSION: This exploratory study showed that, compared to fasting, eating chocolate decreases physiological gall bladder and stomach [18F]-FES uptake; further reduction through a normal diet was not seen. A prospective study is warranted to confirm this finding.

Preclinical PET imaging of bispecific antibody ERY974 targeting CD3 and glypican 3 reveals that tumor uptake correlates to T cell infiltrate.

BACKGROUND: Bispecific antibodies redirecting T cells to the tumor obtain increasing interest as potential cancer immunotherapy. ERY974, a full-length bispecific antibody targeting CD3ε on T cells and glypican 3 (GPC3) on tumors, has been in clinical development However, information on the influence of T cells on biodistribution of bispecific antibodies, like ERY974, is scarce. Here, we report the biodistribution and tumor targeting of zirconium-89 (89Zr) labeled ERY974 in mouse models using immuno-positron emission tomography (PET) imaging. METHODS: To study both the role of GPC3 and CD3 on the biodistribution of [89Zr]Zr-N-suc-Df-ERY974, 89Zr-labeled control antibodies targeting CD3 and non-mammalian protein keyhole limpet hemocyanin (KLH) or KLH only were used. GPC3 dependent tumor targeting of [89Zr]Zr-N-suc-Df-ERY974 was tested in xenograft models with different levels of GPC3 expression. In addition, CD3 influence on biodistribution of [89Zr]Zr-N-suc-Df-ERY974 was evaluated by comparing biodistribution between tumor-bearing immunodeficient mice and mice reconstituted with human immune cells using microPET imaging and ex vivo biodistribution. Ex vivo autoradiography was used to study deep tissue distribution. RESULTS: In tumor-bearing immunodeficient mice, [89Zr]Zr-N-suc-Df-ERY974 tumor uptake was GPC3 dependent and specific over [89Zr]Zr-N-suc-Df-KLH/CD3 and [89Zr]Zr-N-suc-Df-KLH/KLH. In mice engrafted with human immune cells, [89Zr]Zr-N-suc-Df-ERY974 specific tumor uptake was higher than in immunodeficient mice. Ex vivo autoradiography demonstrated a preferential distribution of [89Zr]Zr-N-suc-Df-ERY974 to T cell rich tumor tissue. Next to tumor, highest specific [89Zr]Zr-N-suc-Df-ERY974 uptake was observed in spleen and lymph nodes. CONCLUSION: [89Zr]Zr-N-suc-Df-ERY974 can potentially be used to study ERY974 biodistribution in patients to support drug development.

Molecular imaging to identify patients with metastatic breast cancer who benefit from endocrine treatment combined with cyclin-dependent kinase inhibition.

BACKGROUND: Adding cyclin-dependent kinase (CDK) inhibitor to endocrine treatment improves outcome in œstrogen receptor (ER) positive metastatic breast cancer, but identifying the subset of patients who benefit is challenging. Response is potentially associated with ER expression heterogeneity. This is because, unlike the primary tumour in the breast that is localized to the organ, the metastatic breast cancer has spread and continues to spread to distant locations in the body such as bones, lungs, liver, axial skeleton, even to the central nervous system like the brain, wherefrom obtaining biopsies are not easy, and also, the metastasised tissues are heterogeneous. Positron emission tomography (PET) with 16α-[18F]fluoro-17ß-œstradiol (FES), briefly referred to as FES-PET, allows whole-body ER assessment. We explored whether FES-PET heterogeneity and FES uptake were related to letrozole and palbociclib outcome, in patients with ER positive, metastatic breast cancer. PATIENTS AND METHODS: Patients underwent a baseline FES-PET and 18F-fluorodeoxyglucose (FDG) PET, the FDG-PET served to help identify active sites of breast cancer with contrast-enhanced computed tomography (CT). FES-PET heterogeneity score (% FES positive lesions divided by all lesions on FDG-PET and/or CT) and FES uptake were related to outcome and 8-week FDG-PET response. Circulating tumour DNA (CtDNA) samples for ESR1 mutation analysis were collected at baseline. RESULTS: In 30 patients with 864 metastatic lesions, baseline FES-PET heterogeneity was assessed. In 27 patients with 688 lesions, response was evaluated. Median time to progression (TTP) was 73 weeks (95% confidence interval [CI] 21 to ∞) in 7 patients with 100% FES positive disease, 27 weeks (14-49) in heterogeneous FES positive disease (20 patients), and 15 weeks (9 to ∞) without FES positivity (three patients; log-rank P = 0.30). Geometric mean FES uptake was 2.3 for metabolic progressive patients, 2.5 (Pvs progression = 0.82) for metabolic stable disease, and 3.3 (Pvs progression = 0.40) for metabolic response (Ptrend = 0.21). ESR1 mutations, found in 13/23 patients, were unrelated to FES uptake. CONCLUSION: This exploratory study suggests that FES-PET heterogeneity may potentially identify the subset of ER positive, metastatic breast cancer patients who benefit from letrozole combined with CDK inhibition. CLINICAL TRIAL INFORMATION: NCT02806050.

Visual and quantitative evaluation of [18F]FES and [18F]FDHT PET in patients with metastatic breast cancer: an interobserver variability study.

PURPOSE: Correct identification of tumour receptor status is important for treatment decisions in breast cancer. [18F]FES PET and [18F]FDHT PET allow non-invasive assessment of the oestrogen (ER) and androgen receptor (AR) status of individual lesions within a patient. Despite standardised analysis techniques, interobserver variability can significantly affect the interpretation of PET results and thus clinical applicability. The purpose of this study was to determine visual and quantitative interobserver variability of [18F]FES PET and [18F]FDHT PET interpretation in patients with metastatic breast cancer. METHODS: In this prospective, two-centre study, patients with ER-positive metastatic breast cancer underwent both [18F]FES and [18F]FDHT PET/CT. In total, 120 lesions were identified in 10 patients with either conventional imaging (bone scan or lesions > 1 cm on high-resolution CT, n = 69) or only with [18F]FES and [18F]FDHT PET (n = 51). All lesions were scored visually and quantitatively by two independent observers. A visually PET-positive lesion was defined as uptake above background. For quantification, we used standardised uptake values (SUV): SUVmax, SUVpeak and SUVmean. RESULTS: Visual analysis showed an absolute positive and negative interobserver agreement for [18F]FES PET of 84% and 83%, respectively (kappa = 0.67, 95% CI 0.48-0.87), and 49% and 74% for [18F]FDHT PET, respectively (kappa = 0.23, 95% CI - 0.04-0.49). Intraclass correlation coefficients (ICC) for quantification of SUVmax, SUVpeak and SUVmean were 0.98 (95% CI 0.96-0.98), 0.97 (95% CI 0.96-0.98) and 0.89 (95% CI 0.83-0.92) for [18F]FES, and 0.78 (95% CI 0.66-0.85), 0.76 (95% CI 0.63-0.84) and 0.75 (95% CI 0.62-0.84) for [18F]FDHT, respectively. CONCLUSION: Visual and quantitative evaluation of [18F]FES PET showed high interobserver agreement. These results support the use of [18F]FES PET in clinical practice. In contrast, visual agreement for [18F]FDHT PET was relatively low due to low tumour-background ratios, but quantitative agreement was good. This underscores the relevance of quantitative analysis of [18F]FDHT PET in breast cancer. TRIAL REGISTRATION: ClinicalTrials.gov, NCT01988324. Registered 20 November 2013, https://clinicaltrials.gov/ct2/show/NCT01988324?term=FDHT+PET&draw=1&rank=2.

Consideration of breast cancer subtype in targeting the androgen receptor.

The androgen receptor (AR) is a drug target in breast cancer, and AR-targeted therapies have induced tumor responses in breast cancer patients. In this review, we summarized the role of AR in breast cancer based on preclinical and clinical data. Response to AR-targeted therapies in unselected breast cancer populations is relatively low. Preclinical and clinical data show that AR antagonists might have a role in estrogen receptor (ER)-negative/AR-positive tumors. The prognostic value of AR for patients remains uncertain due to the use of various antibodies and cut-off values for immunohistochemical assessment. To get more insight into the role of AR in breast cancer, we additionally performed a retrospective pooled analysis to determine the prognostic value of the AR using mRNA profiles of 7270 primary breast tumors. Our analysis shows that a higher AR mRNA level is associated with improved disease outcome in patients with ER-positive/human epidermal growth factor receptor 2 (HER2)-negative tumors, but with worse disease outcome in HER2-positive subgroups. In conclusion, next to AR expression, incorporation of additional tumor characteristics will potentially make AR targeting a more valuable therapeutic strategy in breast cancer.

Decalcification of Breast Cancer Bone Metastases With EDTA Does Not Affect ER, PR, and HER2 Results.

In metastatic breast cancer (MBC), expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor-2 (HER2) guides treatment selection. In case of bone-only metastatic disease, ER, PR, and HER2 status assessment may be hampered by decalcification. We aimed to determine the optimal decalcification method, and to study discordance of receptor expression between paired primary breast tumors and optimally decalcified bone metastases. First, decalcification was simulated using acetic acid, hydrochloric/formic acid, and EDTA on 12 primary breast carcinomas. ER, PR, and HER2 immunohistochemistry (IHC) and HER2 in situ hybridization (ISH) were assessed, before and after the 3 decalcification methods. EDTA was considered the optimal method, as it did not affect IHC and as ISH failed in only 1/16 cases. Hydrochloric/formic acid altered ER and PR results, and, with acetic acid and hydrochloric/formic acid, ISH failed in, respectively, 94% and 100%. Second, ER, PR, and HER2 IHC was performed in paired primary tumors and EDTA-decalcified bone metastases obtained from patients with first presentation of MBC. Clinically relevant discordance was defined as changed receptor status with treatment implications. Paired samples of 77 patients, participating in the IMPACT-MBC trial, were evaluable. Hormonal receptor expression change was clinically relevant in 6 patients (7.9%) and HER2 expression change in 1 patient (1.3%). This study shows that EDTA decalcification minimally affects receptor expression results. The incidence of clinically relevant discordance between the primary tumor and bone metastases is low. These findings support that bone biopsies can reliably be used to assess receptor status.