A comparison of prostate cancer bone metastases on 18F-Sodium Fluoride and Prostate Specific Membrane Antigen (18F-PSMA) PET/CT: Discordant uptake in the same lesion

Purpose

Prostate-Specific Membrane Antigen (PSMA) PET/CT has been introduced as a sensitive method for characterizing metastatic prostate cancer. The purpose of this study is to compare the spatial concordance of ¹⁸F-NaF PET/CT and ¹⁸F-PSMA-targeted PET/CT within prostate cancer bone metastases.

Methods

Prostate cancer patients with known bone metastases underwent PSMA-targeted PET/CT (¹⁸F-DCFBC or ¹⁸F-DCFPyL) and ¹⁸F-NaF PET/CT. In pelvic and spinal lesions detected by both radiotracers, regions-of-interest (ROIs) derived by various thresholds of uptake intensity were compared for spatial colocalization. Overlap volume was correlated with uptake characteristics and disease status.

Results

The study included 149 lesions in 19 patients. Qualitatively, lesions exhibited a heterogeneous range of spatial concordance between PSMA and NaF uptake from completely matched to completely discordant. Quantitatively, overlap volume decreased as a function of tracer intensity. and disease status, where lesions from patients with castration-sensitive disease showed higher spatial concordance while lesions from patients with castration-resistant disease demonstrated more frequent spatial discordance.

Conclusion

As metastatic prostate cancer progresses from castration-sensitive to castration-resistant, greater discordance is observed between NaF PET and PSMA PET uptake. This may indicate a possible phenotypic shift to tumor growth that is more independent of bone remodeling via osteoblastic formation.

Biodistribution, Tumor Detection, and Radiation Dosimetry of 18F-5-Fluoro-2'-Deoxycytidine with Tetrahydrouridine in Solid Tumors

In preclinical studies, 5-fluoro-2'-deoxycytidine (FdCyd), an inhibitor of DNA methyltransferase and DNA hypermethylation, has shown treatment efficacy against multiple malignancies by suppressing epigenetic hypermethylation in tumor cells. Several ongoing clinical trials are using FdCyd, and although some patients may respond to this drug, in most patients it is ineffective. Thus, establishing a noninvasive imaging modality to evaluate the distribution of the drug may provide insight into the variable responses. A novel experimental radiopharmaceutical, ¹⁸F-labeled FdCyd, was developed as a companion imaging agent to the nonradioactive form of the drug, FdCyd. We present the first-in-humans radiation dosimetry results and biodistribution of ¹⁸F-FdCyd, administered along with tetrahydrouridine, an inhibitor of cytidine/deoxycytidine deaminase, in patients with a variety of solid tumors undergoing FdCyd therapy. Methods: This phase 0 imaging trial examined the ¹⁸F-FdCyd biodistribution and radiation dosimetry in 5 human subjects enrolled in companion therapy trials. In each subject, 4 sequential PET scans were acquired to estimate whole-body and individual organ effective dose, using OLINDA/EXM, version 1.0. Tumor-to-background ratios were also calculated for the tumor sites visualized on PET/CT imaging. Results: The average whole-body effective dose for the experimental radiopharmaceutical ¹⁸F-FdCyd administered in conjunction with tetrahydrouridine was 2.12E-02 ± 4.15E-03 mSv/MBq. This is similar to the radiation dose estimates for ¹⁸F-FDG PET. The critical organ, with the highest absorbed radiation dose, was the urinary bladder wall at 7.96E-02 mSv/MBq. Other organ doses of note were the liver (6.02E-02mSv/MBq), kidneys (5.26E-02 mSv/MBq), and gallbladder (4.05E-02 mSv/MBq). Tumor target-to-background ratios ranged from 2.4 to 1.4, which potentially enable tumor visualization in static PET images. Conclusion: This phase 0 imaging clinical trial provides evidence that ¹⁸F-FdCyd administered in conjunction with tetrahydrouridine yields acceptable individual organ and whole-body effective doses, as well as modest tumor-to-background ratios that potentially enable tumor visualization. Dose estimates for ¹⁸F-FdCyd are comparable to those for other PET radiopharmaceuticals, such as ¹⁸F-FDG. Further studies with larger study populations are warranted to assess ¹⁸F-FdCyd imaging as a predictor of FdCyd treatment effectiveness.

Keeping up with the prostate-specific membrane antigens (PSMAs): an introduction to a new class of positron emission tomography (PET) imaging agents

Prostate-specific membrane antigen (PSMA) targeted positron emission tomography (PET) is an emerging prostate cancer imaging method, which has been reported to have a higher sensitivity and specificity than the currently approved PET imaging agents. Multiple PSMA ligands are being investigated around the world and applications range from primary tumor characterization, to local staging, biochemical recurrence, metastasis, and image-guided interventions. The most investigated PET tracers are labelled with 68-Gallium or 18-Fluoride and are discussed in this review. Additionally, ^99mTc labeled PSMA agents for single photon emission computed tomography (SPECT) imaging are elucidated as an alternative method of PSMA image acquisition.

First-in-human phase 0 study of 111In-CHX-A"-DTPA trastuzumab for HER2 tumor imaging

Introduction:

Tumors over-expressing the human epithelial receptor 2 (HER2) or exhibiting amplification or mutation of its proto-oncogene have a poorer prognosis. Using trastuzumab and/or other HER2 targeted therapies can increase overall survival in patients with HER2(+) tumors making it critical to accurately identify patients who may benefit. We report on a Phase 0 study of the imaging agent, ¹¹¹In-CHX-A”-DTPA trastuzumab, in patients with known HER2 status to evaluate its safety and biodistribution and to obtain preliminary data regarding its ability to provide an accurate, whole-body, non-invasive means to determine HER2 status.

Methods:

¹¹¹In-CHX-A”-DTPA trastuzumab was radiolabeled on-site and slowly infused into 11 patients who underwent single (n=5) or multiple (n=6) ɣ-camera (n=6) and/or SPECT (n=8) imaging sessions.

Results:

No safety issues were identified. Visual and semi-quantitative imaging data were concordant with tissue HER2 expression profiling in all but 1 patient. The biodistribution showed intense peak liver activity at the initial imaging timepoint (3.3h) and a single-phase clearance fit of the average time-activity curve (TAC) estimated t_1/2=46.9h (R²=0.97; 95%CI 41.8 to 53h). This was followed by high gastrointestinal (GI) tract activity peaking by 52h. Linear regression predicted GI clearance by 201.2h (R² =0.96; 95%CI 188.5 to 216.9h). Blood pool had lower activity with its maximum on the initial images. Non-linear regression fit projected a t_1/2=34.2h (R² =0.96; 95%CI 25.3 to 46.3h). Assuming linear whole-body clearance, linear regression projected complete elimination (x-intercept) at 256.5hr (R²=0.96; 95%CI 186.1 to 489.2h).

Conclusion:

¹¹¹In-CHX-A”-DTPA trastuzumab can be safely imaged in humans. The biodistribution allowed for visual and semiquantitative analysis with results concordant with tissue expression profiling in 10 of 11 patients. Advances in Knowledge and Implications for Patient Care Using readily available components and on-site radiolabeling ¹¹¹In-CHX-A”-DTPA trastuzumab SPECT imaging may provide an economical, non-invasive means to detect HER2 over-expression.

Abstract 3671: Phenotypic heterogeneity within prostate cancer bone metastases measured by 18F-DCFBC PET/CT and 18F-NaF PET/CT

Purpose: The purpose of this study was to compare the spatial colocalization of prostate-specific membrane antigen (PSMA) targeting agent 18F-DCFBC PET/CT, a marker which demonstrates correlation with tumor aggressiveness, and 18F-NaF PET/CT, a marker of osteoblastic activity, within bone lesions of patients with metastatic prostate cancer. Methods: Twenty-eight metastatic prostate cancer patients received 18F-DCFBC PET/CT and 18F-NaF PET/CT scans (median interval 7 days, range 1-57). Tracer-specific regions of interest (ROI) were derived from threshold containing 80% of maximum SUV (SUV80%). Lesion detection and uptake was compared across the two PET/CT agents using non-parametric testing (Spearman correlation, Wilcoxon rank sum) accounting for intra-patient correlation. Lesion-specific registration was completed by global alignment of skeletal segments followed by local neighborhood optimization of area surrounding lesion. Spatial concordance was evaluated using overlap volume (OV), calculated as the volume of ROI intersection (shared volume) relative to the minimum volume of NaF-ROI or PSMA-ROI to account for differences in ROI volumes. Differences in uptake and CT Hounsfield units (HU) were compared within concordant (overlapping) and discordant (NaF-only, PSMA-only) regions of the same lesion using Wilcoxon signed rank test accounting for intra-patient correlation. Results: Twenty-six patients had positive NaF or DCFBC PET/CT scans, with a total of 241 metastatic sites identified. Lesion-level NaF SUV80% and DCFBC-2hr SUV80% were not significantly correlated at baseline (ρ=0.41, p>0.1). Lesion-level NaF-SUV80% was lower in bone lesions detected only by NaF (N=96) compared to NaF-SUV80% in bone lesions detected by both tracers (N=82), nearing significance (p=0.065). This pattern was not observed in DCFBC-SUV80% (p=0.5). To avoid bias from motion artifacts, only lesions in pelvis and spine were considered for voxel-based analysis (N=42). NaF and PSMA ROIs showing varying levels of spatial concordance (OV mean=0.26, range=0-1), which was modestly associated with higher sclerosis (ρ=0.4, p=0.01) and weakly associated with lower PSMA activity (ρ=0.3, p=0.07). Intra-lesion PSMA-only regions were significantly less sclerotic compared to concordant (p=0.04) and NaF-only (p=0.03) regions, indicating regions of active tumor seeding extend beyond regions of active bone remodeling within the tumor. Conclusions: Metastatic seeding and growth of prostate cancer in bone is biologically complex and dependent on bone microenvironment. We find regions of aggressive cellular activity (PSMA-targeting PET/CT) show heterogeneous colocalization with regions of rapid bone remodeling (NaF PET/CT) within sites of metastatic bone disease. These preliminary findings are important for consideration of targeted radionuclide therapies in metastatic prostate cancer.

Citation Format: Stephanie A. Harmon, Esther Mena, Joanna Shih, Ethan Bergvall, Stephen Adler, Sherif Mehralivand, Ravi A. Madan, James L. Gulley, William L. Dahut, Baris Turkbey, Peter L. Choyke, M Liza Lindenberg. Phenotypic heterogeneity within prostate cancer bone metastases measured by 18F-DCFBC PET/CT and 18F-NaF PET/CT [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3671.

A Prospective Comparison of 18F-Sodium Fluoride PET/CT and PSMA-Targeted 18F-DCFBC PET/CT in Metastatic Prostate Cancer

The purpose of this study was to compare the diagnostic performance of ¹⁸F-DCFBC PET/CT, a first-generation ¹⁸F-labeled prostate-specific membrane antigen (PSMA)-targeted agent, and ¹⁸F-NaF PET/CT, a sensitive marker of osteoblastic activity, in a prospective cohort of patients with metastatic prostate cancer. Methods: Twenty-eight prostate cancer patients with metastatic disease on conventional imaging prospectively received up to 4 PET/CT scans. All patients completed baseline ¹⁸F-DCFBC PET/CT and ¹⁸F-NaF PET/CT scans, and 23 patients completed follow-up imaging, with a median follow-up interval of 5.7 mo (range, 4.2-12.6 mo). Lesion detection was compared across the 2 PET/CT agents at each time point. Detection and SUV characteristics of each PET/CT agent were compared with serum prostate-specific antigen (PSA) levels and treatment status at the time of baseline imaging using nonparametric statistical testing (Spearman correlation, Wilcoxon rank). Results: Twenty-six patients had metastatic disease detected on ¹⁸F-NaF or ¹⁸F-DCFBC at baseline, and 2 patients were negative on both scans. Three patients demonstrated soft tissue-only disease. Of 241 lesions detected at baseline, 56 were soft-tissue lesions identified by ¹⁸F-DCFBC only and 185 bone lesions detected on ¹⁸F-NaF or ¹⁸F-DCFBC. ¹⁸F-NaF detected significantly more bone lesions than ¹⁸F-DCFBC (P < 0.001). Correlation of PSA with patient-level SUV metrics was strong in ¹⁸F-DCFBC (ρ > 0.5, P < 0.01) and poor in ¹⁸F-NaF (ρ < 0.3, P > 0.1). When PSA levels were combined with treatment status, patients with below-median levels of PSA (<2 ng/mL) on androgen deprivation therapy (n = 11) demonstrated more lesions on ¹⁸F-NaF than ¹⁸F-DCFBC (P = 0.02). In PSA greater than 2 ng/mL, patients on androgen deprivation therapy (n = 8) showed equal to or more lesions on ¹⁸F-DCFBC than on ¹⁸F-NaF. Conclusion: The utility of PSMA-targeting imaging in metastatic prostate cancer appears to depend on patient disease course and treatment status. Compared with ¹⁸F-NaF PET/CT, ¹⁸F-DCFBC PET/CT detected significantly fewer bone lesions in the setting of early or metastatic castrate-sensitive disease on treatment. However, in advanced metastatic castrate-resistant prostate cancer, ¹⁸F-DCFBC PET/CT shows good concordance with NaF PET/CT.

Results of phase I plus expansion cohorts of cabozantinib (Cabo) plus nivolumab (Nivo) and CaboNivo plus ipilimumab (Ipi) in patients (pts) with with metastatic urothelial carcinoma (mUC) and other genitourinary (GU) malignancies

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Background: Tolerability and efficacy of CaboNivo and CaboNivoIpi were demonstrated in the initial phase I cohort, prompting longer follow-up and the addition of expansion cohorts to further evaluate both combinations Methods: Phase I cohort had 7 dose levels (DL). Recommended phase 2 doses for CaboNivo=Cabo 40mg/Nivo 3mg/kg (DL2) & CaboNivoIpi=Cabo 40mg/Nivo 3mg/kg/Ipi 1mg/kg (DL6) (Nadal ESMO 2017).In expansion cohorts, pts were treated: [1] DL8: Cabo 40mg/Nivo 1mg/kg/Ipi 3mg/kg; [2]DL2: mUC, metastatic renal cell carcinoma (mRCC), adenocarcinoma bladder (AcB): post-PD-1-PDL1 inhibitor mUC (p-mUC), and [3] DL6 mRCC. Objectives: safety, objective response rate (ORR), duration of response (DOR), progression-free survival (PFS) & overall survival (OS). Results: 75 pts enrolled. Median age 59 yo. 83% male, 17% female. 47 treated with CaboNivo (mUC n=24; AcB n= 9; germ cell tumor (GCT) n= 5; castrate-resistant prostate cancer (CRPC) n= 4; bladder squamous cell carcinoma (SCC) n= 2; penile n=1; mRCC n= 7). 28 treated with CaboNivoIpi: (mUC n=8; penile n=3; CRPC n=7; Sertoli n=1; mRCC n=6; bladder small cell carcinoma n=1; renal medullary carcinoma (RMC) n=2). Any grade (G) adverse events (AEs) (CaboNivo 96% & CaboNivoIpi 96%)/G3–4 AEs (CaboNivo 62% & CaboNivoIpi 71%). Most common any G, CaboNivo: fatigue 70%, diarrhea 60%, AST/ALT 60%, hypophosphatemia (hypoP) 45% & CaboNivoIpi: fatigue 71%, diarrhea 68%, hypoP 50%, AST/ALT 43%. Most common G3-4, CaboNivo: lipase 17%, hypoP 15%, fatigue 6% & CaboNivoIpi: hypoP 21%, AST/ALT 14%, lipase 14%. Selected irAs: colitis (2.6%), hepatitis (2.6%), pneumonitis (2.6%), aseptic meningitis (1.3%). ORR: 36%; 3CR (2mUC, 1SCC) & 20PR (5mUC, 2SCC, 7mRCC, 2Penile, 2AcB, 1CRPC, 1RMC). mDOR: 24.1 mo [95% CI: 14.7-NR], mPFS: 7.2 mo [95%CI: 5.1-18.4], mOS:18.8 mo [95%CI: 10.6-NR]. OS 6/12 mo: 83%/61%. Cohort of p-mUC pts(n=5):1PR/3SD/1PD Conclusions: Updated results from phase I and expanded cohorts confirm initial safety findings and promising antitumor activity for both combinations in mUC, mRCC, and rare GU malignancies Clinical trial information: NCT02496208.

Combined model-based and patient-specific dosimetry for 18F-DCFPyL, a PSMA-targeted PET agent

PURPOSE

Prostate-specific membrane antigen (PSMA), a type-II integral membrane protein highly expressed in prostate cancer, has been extensively used as a target for imaging and therapy. Among the available PET radiotracers, the low molecular weight agents that bind to PSMA are proving particularly effective. We present the dosimetry results for ¹⁸F-DCFPyL in nine patients with metastatic prostate cancer.

METHODS

Nine patients were imaged using sequential PET/CT scans at approximately 1, 12, 35 and 70 min, and a final PET/CT scan at approximately 120 min after intravenous administration of 321 ± 8 MBq (8.7 ± 0.2 mCi) of¹⁸F-DCFPyL. Time-integrated-activity coefficients were calculated and used as input in OLINDA/EXM software to obtain dose estimates for the majority of the major organs. The absorbed doses (AD) to the eye lens and lacrimal glands were calculated using Monte-Carlo models based on idealized anatomy combined with patient-specific volumes and activity from the PET/CT scans. Monte-Carlo based models were also developed for calculation of the dose to two major salivary glands (parotid and submandibular) using CT-based patient-specific gland volumes.

RESULTS

The highest calculated mean AD per unit administered activity of ¹⁸F was found in the lacrimal glands, followed by the submandibular glands, kidneys, urinary bladder wall, and parotid glands. The S-values for the lacrimal glands to the eye lens (0.42 mGy/MBq h), the tear film to the eye lens (1.78 mGy/MBq h) and the lacrimal gland self-dose (574.10 mGy/MBq h) were calculated. Average S-values for the salivary glands were 3.58 mGy/MBq h for the parotid self-dose and 6.78 mGy/MBq h for the submandibular self-dose. The resultant mean effective dose of ¹⁸F-DCFPyL was 0.017 ± 0.002 mSv/MBq.

CONCLUSIONS

¹⁸F-DCFPyL dosimetry in nine patients was obtained using novel models for the lacrimal and salivary glands, two organs with potentially dose-limiting uptake for therapy and diagnosis which lacked pre-existing models.

PSMA-Based [(18)F]DCFPyL PET/CT Is Superior to Conventional Imaging for Lesion Detection in Patients with Metastatic Prostate Cancer

PURPOSE

Current standard of care conventional imaging modalities (CIM) such as X-ray computed tomography (CT) and bone scan can be limited for detection of metastatic prostate cancer and therefore improved imaging methods are an unmet clinical need. We evaluated the utility of a novel second-generation low molecular weight radiofluorinated prostate-specific membrane antigen (PSMA)-targeted positron emission tomography (PET) radiotracer, [(18)F]DCFPyL, in patients with metastatic prostate cancer.

PROCEDURES

Nine patients with suspected prostate cancer recurrence, eight with CIM evidence of metastatic prostate cancer and one with biochemical recurrence, were imaged with [(18)F]DCFPyL PET/CT. Eight of the patients had contemporaneous CIM for comparison. A lesion-by-lesion comparison of the detection of suspected sites of metastatic prostate cancer was carried out between PET and CIM. Statistical analysis for estimated proportions of inter-modality agreement for detection of metastatic disease was calculated accounting for intra-patient correlation using general estimating equation (GEE) intercept-only regression models.

RESULTS

One hundred thirty-nine sites of PET positive [(18)F]DCFPyL uptake (138 definite, 1 equivocal) for metastatic disease were detected in the eight patients with available comparison CIM. By contrast, only 45 lesions were identified on CIM (30 definite, 15 equivocal). When lesions were negative or equivocal on CIM, it was estimated that a large portion of these lesions or 0.72 (95 % confidence interval (CI) 0.55-0.84) would be positive on [(18)F]DCFPyL PET. Conversely, of those lesions negative or equivocal on [(18)F]DCFPyL PET, it was estimated that only a very small proportion or 0.03 (95 % CI 0.01-0.07) would be positive on CIM. Delayed 2-h-post-injection time point PET yielded higher tumor radiotracer uptake and higher tumor-to-background ratios than an earlier 1-h-post-injection time point.

CONCLUSIONS

A novel PSMA-targeted PET radiotracer, [(18)F]DCFPyL, was able to a large number of suspected sites of prostate cancer, many of which were occult or equivocal by CIM. This study provides strong preliminary evidence for the use of this second-generation PSMA-targeted PET radiotracer for detection of metastatic prostate cancer and lends further support for the importance of PSMA-targeted PET imaging in prostate cancer.

Clinical impact of PSMA-based 18F-DCFBC PET/CT imaging in patients with biochemically recurrent prostate cancer after primary local therapy

PURPOSE

The purpose of our study was to assess ¹⁸F-DCFBC PET/CT, a PSMA targeted PET agent, for lesion detection and clinical management of biochemical relapse in prostate cancer patients after primary treatment.

METHODS

This is a prospective IRB-approved study of 68 patients with documented biochemical recurrence after primary local therapy consisting of radical prostatectomy (n = 50), post radiation therapy (n = 9) or both (n = 9), with negative conventional imaging. All 68 patients underwent whole-body ¹⁸F-DCFBC PET/CT, and 62 also underwent mpMRI within one month. Lesion detection with ¹⁸F-DCFBC was correlated with mpMRI findings and pre-scan PSA levels. The impact of ¹⁸F-DCFBC PET/CT on clinical management and treatment decisions was established after 6 months' patient clinical follow-up.

RESULTS

Forty-one patients (60.3%) showed at least one positive ¹⁸F-DCFBC lesion, for a total of 79 lesions, 30 in the prostate bed, 39 in lymph nodes, and ten in distant sites. Tumor recurrence was confirmed by either biopsy (13/41 pts), serial CT/MRI (8/41) or clinical follow-up (15/41); there was no confirmation in five patients, who continue to be observed. The ¹⁸F-DCFBC and mpMRI findings were concordant in 39 lesions (49.4%), and discordant in 40 lesions (50.6%); the majority (n = 32/40) of the latter occurring because the recurrence was located outside the mpMRI field of view. ¹⁸F-DCFBC PET positivity rates correlated with PSA values and 15%, 46%, 83%, and 77% were seen in patients with PSA values <0.5, 0.5 to <1.0, 1.0 to <2.0, and ≥2.0 ng/mL, respectively. The optimal cut-off PSA value to predict a positive ¹⁸F-DCFBC scan was 0.78 ng/mL (AUC = 0.764). A change in clinical management occurred in 51.2% (21/41) of patients with a positive ¹⁸F-DCFBC result, generally characterized by starting a new treatment in 19 patients or changing the treatment plan in two patients.

CONCLUSIONS

¹⁸F-DCFBC detects recurrences in 60.3% of a population of patients with biochemical recurrence, but results are dependent on PSA levels. Above a threshold PSA value of 0.78 ng/mL, ¹⁸F-DCFBC was able to identify recurrence with high reliability. Positive ¹⁸F-DCFBC PET imaging led clinicians to change treatment strategy in 51.2% of patients.

Precision Medicine and PET/Computed Tomography in Melanoma

Recent advances in genomic profiling and sequencing of melanoma have provided new insights into the development of the basis for molecular biology to more accurately subgroup patients with melanoma. The development of novel mutation-targeted and immunomodulation therapy as a major component of precision oncology has revolutionized the management and outcome of patients with metastatic melanoma. PET imaging plays an important role in noninvasively assessing the tumor biological behavior, to guide individualized treatment and assess response to therapy. This review summarizes the recent genomic discoveries in melanoma in the era of targeted therapy and their implications for functional PET imaging.

Combined FDG and NaF PET/CT study in patients (pts) with metastatic genitourinary tumors (mGU) treated with cabozantinib + nivolumab +/- ipilimumab (CaboNivo+/-Ipi)

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Background: The primary objective of the study is to assess the feasibility of obtaining combined FDG and NaF PET/CT in detecting soft-tissue and bone metastatic disease in mGU pts treated with CaboNivo+/-Ipi. Methods: Pts in this single-arm, multicenter, phase I trial had FDG PET/CT followed by NaF PET/CT within 1 hour, at baseline and 8 weeks. The number and location of metastatic lesions on FDG PET/CT and on NaF PET/CT were captured. Lesions were considered positive when there was focal abnormal radiotracer uptake with CT correlation. We analyzed soft tissue and bone lesions distribution and the concordance of baseline metastatic bone disease. Results: From 7/14/15 to 9/9/16, 27 pts (urothelial carcinoma N = 11, bladder squamous cell carcinoma N = 2, sarcomatoid renal cancer N = 1, sertoli cell N = 1, germ cell tumor N = 4, trophoblastic testicular cancer N = 1, urachal N = 4, castrate-resistant prostate cancer N = 2, prostate neuroendocrine N = 1) had scans. Median age was 55 (range 35-75 yr), 24 (89%) were male. Pts completed the dual PET/CTs on the same day (imaging time 3-4 hours) without complications. On FDG, the distribution of 340 lesions were lymph node 41%, bone 35%, lung 18%, liver 11%, soft tissue 4%, kidney 0.6%, adrenal 0.3%, spleen 0.3%, pancreas 0.3%. On NaF, the distribution of 130 lesions was spine 33%, rib 16%, pelvis 13%, femur 10%, scapula 9%, sacrum 8%, skull 5%, humerus 4%, sternum 3%, manubrium 2%, clavicle 2%. Of the 130 lesions on FDG/NaF PET/CT, 38% were not seen on initial FDG. The combination of the two tracers did not affect the quality of the PET/CTs given distinct radiotracer uptake in the anatomical locations with no distortions. Residual FDG activity on combined FDG-NaF images required background intensity to be adjusted to delineate focal radiotracer uptake. There was no difficulty in identifying metastatic lesions, and no instances of prior FDG uptake affecting the determination of metastatic disease. Conclusions: Combination FDG-NaF PET/CT is a feasible imaging modality that offers convenience to pts without compromising detection of metastatic disease in mGU pts. FDG alone detected fewer bone lesions than combined FDG-NaF PET/CT. Clinical trial information: NCT02496208.

Evaluation of Prostate Cancer with PET/MRI

In the ongoing effort to understand and cure prostate cancer, imaging modalities are constantly evolving to assist in clinical decisions. Multiparametric MRI can be used to direct prostate biopsies, improve diagnostic yield, and help clinicians make more accurate decisions. PET is superior in providing biologic information about the cancer and is sensitive and highly specific. Integrated PET/MRI is a welcome technical advance with great potential to influence the diagnosis and management of prostate cancer in clinical practice.

Practical no-gold-standard evaluation framework for quantitative imaging methods: application to lesion segmentation in positron emission tomography

Recently, a class of no-gold-standard (NGS) techniques have been proposed to evaluate quantitative imaging methods using patient data. These techniques provide figures of merit (FoMs) quantifying the precision of the estimated quantitative value without requiring repeated measurements and without requiring a gold standard. However, applying these techniques to patient data presents several practical difficulties including assessing the underlying assumptions, accounting for patient-sampling-related uncertainty, and assessing the reliability of the estimated FoMs. To address these issues, we propose statistical tests that provide confidence in the underlying assumptions and in the reliability of the estimated FoMs. Furthermore, the NGS technique is integrated within a bootstrap-based methodology to account for patient-sampling-related uncertainty. The developed NGS framework was applied to evaluate four methods for segmenting lesions from F-Fluoro-2-deoxyglucose positron emission tomography images of patients with head-and-neck cancer on the task of precisely measuring the metabolic tumor volume. The NGS technique consistently predicted the same segmentation method as the most precise method. The proposed framework provided confidence in these results, even when gold-standard data were not available. The bootstrap-based methodology indicated improved performance of the NGS technique with larger numbers of patient studies, as was expected, and yielded consistent results as long as data from more than 80 lesions were available for the analysis.

Imaging metastatic prostate cancer with 18F-DCFBC PET/CT (DCFBC) and 18F-NaF PET/CT (NaF)

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Background: Conventional imaging of advanced prostate cancer (computerized tomography and nuclear bone scintigraphy) is limited and indicates a need for a more specific molecular imaging probe. DCFBC is a radiolabeled PET agent that binds with high affinity to prostate specific membrane antigen (PSMA), which is overexpressed in almost all prostate cancers and through whole-body non-invasive functional imaging, may provide new information on the expression of PSMA. We compare the uptake of DCFBC in bone with respect to NaF PET/CT in metastatic prostate cancer patients. DCFBC has added capability to detect soft tissue metastasis whereas NaF is confined to secondary effects of bone disease. Methods: Subjects with known or suspected prostate cancer metastasis underwent DCFBC PET/CT imaging performed at 1 hour and 2 hours after IV bolus injection of 8 mCi of DCFBC. Patients also underwent a whole body NaF PET/CT scan within 3 weeks of DCFBC PET/CT to assess for bone metastases. Patients received 3 mCi of NaF IV bolus and then were imaged 1hour post injection. PSA levels and antiandrogen therapy status were obtained at the time of DCFBC imaging. Results: Fifteen patients have been preliminarily analyzed. PSA ranged from < .01 to 4379 ng/mL. NaF identified bone lesions in 10 patients but matching focal DCFBC uptake was only seen in 3 patients. DCFBC additionally showed lymph node metastasis in 1of these 3 patient. There were 5 patients without focal abnormal bone uptake on NaF or DCFBC. In this group, 4 of 5 patients had focal DCFBC uptake in lymph nodes or soft tissue lesions. Ten patients were on some form of androgen deprivation therapy (ADT). For those on ADT, 7 of 10 patients had positive findings on NaF, compared to 2 of 10 patients on DCFBC. Conclusions: DCFBC uptake in bone metastasis does not routinely correspond to focal NaF uptake which could be due to distinct mechanisms of tracer uptake and tumor biology. There is an inverse association in focal bone findings when comparing each tracer on antiandrogen therapy. Through whole-body non-invasive functional imaging and further study, DCFBC may prove useful in characterizing prostate cancer based on PSMA expression. Clinical trial information: NCT02190279.

The Value of FDG PET/CT in Treatment Response Assessment, Follow-Up, and Surveillance of Lung Cancer

OBJECTIVE

The purpose of this article is to summarize the evidence regarding the role of FDG PET/CT in treatment response assessment and surveillance of lung cancer and to provide suggested best practices.

CONCLUSION

FDG PET/CT is a valuable imaging tool for assessing treatment response for patients with lung cancer, though evidence for its comparative effectiveness with chest CT is still evolving. FDG PET/CT is most useful when there is clinical suspicion or other evidence for disease recurrence or metastases. The sequencing, cost analysis, and comparative effectiveness of FDG PET/CT and conventional imaging modalities in the follow-up setting need to be investigated.

Clinical Indications and Impact on Management: Fourth and Subsequent Posttherapy Follow-up 18F-FDG PET/CT Scans in Oncology Patients

The Centers for Medicare and Medicaid Services coverage includes 3 posttherapy ¹⁸F-FDG PET/CT scans per patient and per tumor type. Any additional follow-up ¹⁸F-FDG PET/CT scans will be reimbursed at the discretion of a local Medicare administrator, if deemed medically necessary. This study aimed to investigate common clinical indications for performing a fourth or additional follow-up ¹⁸F-FDG PET/CT scans that could affect the management of patients. Methods: This was a retrospective institutional review of 433 oncology patients (203 men; mean age, 55 y), including a total of 1,659 fourth or subsequent follow-up PET/CT scans after completion of primary treatment. Twelve indications for performing a fourth or subsequent follow-up PET/CT scan were determined, and the impact of each of the 12 indications on patients' management was evaluated. Results: The primary tumors were breast cancer (92 patients, 426 scans), non-Hodgkin lymphoma (77 patients, 208 scans), Hodgkin disease (41 patients, 182 scans), colorectal cancer (70 patients, 286 scans), melanoma (69 patients, 271 scans), and lung cancer (84 patients, 286 scans). The indications were categorized in 4 groups: PET/CT for diagnosis of tumor recurrence (303/1,659, 18.3%), PET/CT before starting therapy for tumor recurrence (64/1,659, 3.9%), PET/CT to assess therapy response for tumor recurrence (507/1,659, 30.6%), and follow-up PET/CT after completion of treatment for tumor recurrence (785/1,659, 47.3%). Overall, fourth and subsequent follow-up ¹⁸F-FDG PET/CT scans resulted in change in management in 31.6% of the scans (356 of 1,128) when the scans were obtained for medical necessities (indications 1-11), and in 5.6% of the scans (30/531) when the scans were obtained without any medical necessity (indication 12). Conclusion: The fourth and subsequent PET/CT scans obtained after completion of primary treatment led to a change in management in 31.6% of the scans when acquired for appropriate clinical reasons. Performing follow-up PET/CT without appropriate medical reason had a low impact on patients' management and should be avoided.

Molecular Imaging and Precision Medicine: PET/Computed Tomography and Therapy Response Assessment in Oncology

A variety of methods have been developed to assess tumor response to therapy. Standardized qualitative criteria based on 18F-fluoro-deoxyglucose PET/computed tomography have been proposed to evaluate the treatment effectiveness in specific cancers and these allow more accurate therapy response assessment and survival prognostication. Multiple studies have addressed the utility of the volumetric PET biomarkers as prognostic indicators but there is no consensus about the preferred segmentation methodology for these metrics. Heterogeneous intratumoral uptake was proposed as a novel PET metric for therapy response assessment. PET imaging techniques will be used to study the biological behavior of cancers during therapy.

Molecular Imaging and Precision Medicine in Head and Neck Cancer

The concept of using tumor genomic profiling information has revolutionized personalized cancer treatment. Head and neck (HN) cancer management is being influenced by recent discoveries of activating mutations in epidermal growth factor receptor and related targeted therapies with tyrosine kinase inhibitors, targeted therapies for Kristen Rat Sarcoma, and MET proto-oncogenes. Molecular imaging using PET plays an important role in assessing the biologic behavior of HN cancer with the goal of delivering individualized cancer treatment. This review summarizes recent genomic discoveries in HN cancer and their implications for functional PET imaging in assessing response to targeted therapies, and drug resistance mechanisms.

Advancement of MR and PET/MR in Prostate Cancer

Multiparametric magnetic resonance (mpMRI) imaging has assumed a larger role in the diagnosis and management of prostate cancer. The current method of detecting prostate cancer relies on blind systematic biopsy, guided only by transrectal ultrasound that generally directs the needle biopsy to sextants of the prostate rather than specific lesions. MpMRI is playing an increasing role in the detection of primary cancer as it can visualize cancers and direct biopsies. However, even mpMRI is inherently nonspecific and numerous biopsies performed under MR guidance prove to be negative. Positron emission tomography (PET) has the potential to improve the sensitivity and specificity for prostate cancer in combination with mpMRI. Prostate-specific membrane antigen is a widely expressed tumor antigen in prostate cancer for which multiple PET ligands, labeled with ⁶⁸Ga and ¹⁸F, are being developed. However, the low spatial resolution of PET mandates that it be combined with a higher resolution imaging modality, which typically has been computed tomography (CT). However, MRI is not only better at localizing lesions in the prostate and prostatic bed, but it is also more sensitive than CT for early bone marrow changes in bone metastases caused by prostate cancer. Prostate-specific membrane antigen-based PET agents show promise in the early detection of recurrent and metastatic disease. Recent developments in hybrid imaging now allow PET/MRI to be performed simultaneously on a single scanner allowing one-to-one correspondence between the PET activity and MRI findings. This offers the opportunity for both high sensitivity and specificity with excellent anatomic location and could allow for more targeted biopsies and treatments. Here, we review the current status of PET/MRI for prostate cancer.

FDG-PET/CT and MRI for Evaluation of Pathologic Response to Neoadjuvant Chemotherapy in Patients With Breast Cancer: A Meta-Analysis of Diagnostic Accuracy Studies

INTRODUCTION

This study compared the diagnostic test accuracy of magnetic resonance imaging (MRI) with that of (18)F-fluoro-2-glucose-positron emission tomography/computed tomography (FDG-PET/CT) imaging in assessment of response to neoadjuvant chemotherapy (NAC) in breast cancer.

METHODS

A systematic search was performed in PubMed and EMBASE (last updated in June 2015). Studies investigating the performance of MRI and FDG-PET or FDG-PET/CT imaging during or after completion of NAC in patients with histologically proven breast cancer were eligible for inclusion. We considered only studies reporting a direct comparison between these imaging modalities to establish precise summary estimates in the same setting of patients. Pathologic response was considered as the reference standard. Two authors independently screened and selected studies that met the inclusion criteria and extracted the data.

RESULTS

A total of 10 studies were included. The pooled estimates of sensitivity and specificity across all included studies were 0.71 and 0.77 for FDG-PET/CT (n = 535) and 0.88 and 0.55 for MRI (n = 492), respectively. Studies were subgrouped according to the time of therapy assessment. In the intra-NAC setting, FDG-PET/CT imaging outperformed MRI with fairly similar pooled sensitivity (0.91 vs. 0.89) and higher specificity (0.69 vs. 0.42). However, MRI appeared to have higher diagnostic accuracy than FDG-PET/CT imaging when performed after the completion of NAC, with significantly higher sensitivity (0.88 vs. 0.57).

CONCLUSION

Analysis of the available studies of patients with breast cancer indicates that the timing of imaging for NAC-response assessment exerts a major influence on the estimates of diagnostic accuracy. FDG-PET/CT imaging outperformed MRI in intra-NAC assessment, whereas the overall performance of MRI was higher after completion of NAC, before surgery.

IMPLICATIONS FOR PRACTICE

The timing of therapy assessment imaging exerts a major influence on overall estimates of diagnostic accuracy. (18)F-fluoro-2-glucose-positron emission tomography (FDG-PET)/computed tomography (CT) imaging outperformed magnetic resonance imaging (MRI) in intra-neoadjuvant chemotherapy assessment with fairly similar pooled sensitivity and higher specificity. However, MRI appeared to be more accurate than FDG-PET/CT in predicting pathologic response when used in the post-therapy setting.

Bone marrow abnormalities and early bone lesions in multiple myeloma and its precursor disease: a prospective study using functional and morphologic imaging

The incidence and importance of bone marrow involvement and/or early bone lesions in multiple myeloma (MM) precursor diseases is largely unknown. This study prospectively compared the sensitivity of several imaging modalities in monoclonal gammopathy of undetermined significance (MGUS), smoldering multiple myeloma (SMM) and MM. Thirty patients (10 each with MGUS, SMM and MM) were evaluated with skeletal survey, [18F]FDG-PET/CT, [18F]NaF-PET/CT and morphologic dynamic contrast enhanced (DCE)-MRI. An additional 16 SMM patients had skeletal surveys and FDG-PET/CT. Among MGUS patients, DCE-MRI found only one focal marrow abnormality; other evaluations were negative. Among 26 SMM patients, five (19%) were re-classified as MM based on lytic bone lesions on CT and six had unifocal or diffuse marrow abnormality. Among MM, marrow abnormalities were observed on FDG-PET/CT in 8/10 patients and on DCE-MRI in nine evaluable patients. Abnormal NaF uptake was observed only in MM patients with lytic lesions on CT, providing no additional clinical information.

(18)F-Flourodeoxy-Glucose PET/Computed Tomography in Brain Tumors: Value to Patient Management and Survival Outcomes

(18)F-flourodeoxy-glucose (FDG) PET/computed tomography (CT) is most useful in the evaluation of primary central nervous system (CNS) lymphoma, important in diagnosis, pretherapy prognosis, and therapy response evaluation. Utility in working up gliomas is less effective, and FDG PET/CT is most helpful when MR imaging is unclear. FDG avidity correlates with the grade of gliomas. FDG PET/CT can be used to noninvasively identify malignant transformation. Establishing this change in the disease process has significant effects on patient management and survival outcome.

Effect of electric field on the performance of soil electro-bioremediation with a periodic polarity reversal strategy

In this work, it is studied the effect of the electric fields (within the range 0.0-1.5 V cm(-1)) on the performance of electrobioremediation with polarity reversal, using a bench scale plant with diesel-spiked kaolinite with 14-d long tests. Results obtained show that the periodic changes in the polarity of the electric field results in a more efficient treatment as compared with the single electro-bioremediation process, and it does not require the addition of a buffer to keep the pH within a suitable range. The soil heating was not very important and it did not cause a change in the temperature of the soil up to values incompatible with the life of microorganisms. Low values of water transported by the electro-osmosis process were attained with this strategy. After only 14 d of treatment, by using the highest electric field studied in this work (1.5 V cm(-1)), up to 35.40% of the diesel added at the beginning of the test was removed, value much higher than the 10.5% obtained by the single bioremediation technology in the same period.

Prospective Study Evaluating Na18F PET/CT in Predicting Clinical Outcomes and Survival in Advanced Prostate Cancer

This prospective pilot study evaluated the ability of Na(18)F PET/CT to detect and monitor bone metastases over time and its correlation with clinical outcomes and survival in advanced prostate cancer.

METHODS

Sixty prostate cancer patients, including 30 with and 30 without known bone metastases by conventional imaging, underwent Na(18)F PET/CT at baseline, 6 mo, and 12 mo. Positive lesions were verified on follow-up scans. Changes in SUVs and lesion number were correlated with prostate-specific antigen change, clinical impression, and overall survival.

RESULTS

Significant associations included the following: SUV and prostate-specific antigen percentage change at 6 mo (P = 0.014) and 12 mo (P = 0.0005); SUV maximal percentage change from baseline and clinical impression at 6 mo (P = 0.0147) and 6-12 mo (P = 0.0053); SUV change at 6 mo and overall survival (P = 0.018); number of lesions on Na(18)F PET/CT and clinical impression at baseline (P < 0.0001), 6 mo (P = 0.0078), and 12 mo (P = 0.0029); and number of lesions on Na(18)F PET/CT per patient at baseline and overall survival (P = 0.017). In an exploratory analysis, paired (99m)Tc-methylene diphosphonate bone scans ((99m)Tc-BS) were available for 35 patients at baseline, 19 at 6 mo, and 14 at 12 mo (68 scans). Malignant lesions on Na(18)F PET/CT (n = 57) were classified on (99m)Tc-BS as malignant 65% of the time, indeterminate 25% of the time, and negative 10% of the time. Additionally, 69% of paired scans showed more lesions on Na(18)F PET/CT than on (99m)Tc-BS.

CONCLUSION

The baseline number of malignant lesions and changes in SUV on follow-up Na(18)F PET/CT significantly correlate with clinical impression and overall survival. Na(18)F PET/CT detects more bone metastases earlier than (99m)Tc-BS and enhances detection of new bone disease in high-risk patients.

Comparison of Prostate-Specific Membrane Antigen-Based 18F-DCFBC PET/CT to Conventional Imaging Modalities for Detection of Hormone-Naïve and Castration-Resistant Metastatic Prostate Cancer

Conventional imaging modalities (CIMs) have limited sensitivity and specificity for detection of metastatic prostate cancer. We examined the potential of a first-in-class radiofluorinated small-molecule inhibitor of prostate-specific membrane antigen (PSMA), N-[N-[(S)-1,3-dicarboxypropyl]carbamoyl]-4-(18)F-fluorobenzyl-l-cysteine ((18)F-DCFBC), to detect metastatic hormone-naïve (HNPC) and castration-resistant prostate cancer (CRPC).

METHODS

Seventeen patients were prospectively enrolled (9 HNPC and 8 CRPC); 16 had CIM evidence of new or progressive metastatic prostate cancer and 1 had high clinical suspicion of metastatic disease. (18)F-DCFBC PET/CT imaging was obtained with 2 successive PET scans starting at 2 h after injection. Patients were imaged with CIM at approximately the time of PET. A lesion-by-lesion analysis of PET to CIM was performed in the context of either HNPC or CRPC. The patients were followed with available clinical imaging as a reference standard to determine the true nature of identified lesions on PET and CIM.

RESULTS

On the lesion-by-lesion analysis, (18)F-DCFBC PET was able to detect a larger number of lesions (592 positive with 63 equivocal) than CIM (520 positive with 61 equivocal) overall, in both HNPC and CRPC patients. (18)F-DCFBC PET detection of lymph nodes, bone lesions, and visceral lesions was superior to CIM. When intrapatient clustering effects were considered, (18)F-DCFBC PET was estimated to be positive in a large proportion of lesions that would be negative or equivocal on CIM (0.45). On follow-up, the sensitivity of (18)F-DCFBC PET (0.92) was superior to CIM (0.71). (18)F-DCFBC tumor uptake was increased at the later PET time point (~2.5 h after injection), with background uptake showing a decreasing trend on later PET.

CONCLUSION

PET imaging with (18)F-DCFBC, a small-molecule PSMA-targeted radiotracer, detected more lesions than CIM and promises to diagnose and stage patients with metastatic prostate cancer more accurately than current imaging methods.

Safety and biodistribution of 111In-amatuximab in patients with mesothelin expressing cancers using single photon emission computed tomography-computed tomography (SPECT-CT) imaging

Amatuximab is a chimeric high-affinity monoclonal IgG1/k antibody targeting mesothelin that is being developed for treatment of mesothelin-expressing cancers. Considering the ongoing clinical development of amatuximab in these cancers, our objective was to characterize the biodistribution, and dosimetry of ¹¹¹Indium (¹¹¹In) radiolabelled amatuximab in mesothelin-expressing cancers. Between October 2011 and February 2013, six patients including four with malignant mesothelioma and two with pancreatic adenocarcinoma underwent Single Photon Emission Computed Tomography-Computed Tomography (SPECT/CT) imaging following administration of ¹¹¹In amatuximab. SPECT/CT images were obtained at 2–4 hours, 24–48 hours and 96–168 hours after radiotracer injection. In all patients, tumor to background ratios (TBR) consistently met or exceeded an uptake of 1.2 (range 1.2–62.0) which is considered the minimum TBR that can be visualized. TBRs were higher in tumors of patients with mesothelioma than pancreatic adenocarcinoma. ¹¹¹In-amatuximab uptake was noted in both primary tumors and metastatic sites. The radiotracer dose was generally well-tolerated and demonstrated physiologic uptake in the heart, liver, kidneys and spleen. This is the first study to show tumor localization of an anti-mesothelin antibody in humans. Our results show that ¹¹¹In-amatuximab was well tolerated with a favorable dosimetry profile. It localizes to mesothelin expressing cancers with a higher uptake in mesothelioma than pancreatic cancer.

Head and neck PET/CT: therapy response interpretation criteria (Hopkins Criteria)-interreader reliability, accuracy, and survival outcomes

There has been no established qualitative system of interpretation for therapy response assessment using PET/CT for head and neck cancers. The objective of this study was to validate the Hopkins interpretation system to assess therapy response and survival outcome in head and neck squamous cell cancer patients (HNSCC).

METHODS

The study included 214 biopsy-proven HNSCC patients who underwent a posttherapy PET/CT study, between 5 and 24 wk after completion of treatment. The median follow-up was 27 mo. PET/CT studies were interpreted by 3 nuclear medicine physicians, independently. The studies were scored using a qualitative 5-point scale, for the primary tumor, for the right and left neck, and for overall assessment. Scores 1, 2, and 3 were considered negative for tumors, and scores 4 and 5 were considered positive for tumors. The Cohen κ coefficient (κ) was calculated to measure interreader agreement. Overall survival (OS) and progression-free survival (PFS) were analyzed by Kaplan-Meier plots with a Mantel-Cox log-rank test and Gehan Breslow Wilcoxon test for comparisons.

RESULTS

Of the 214 patients, 175 were men and 39 were women. There was 85.98%, 95.33%, 93.46%, and 87.38% agreement between the readers for overall, left neck, right neck, and primary tumor site response scores, respectively. The corresponding κ coefficients for interreader agreement between readers were, 0.69-0.79, 0.68-0.83, 0.69-0.87, and 0.79-0.86 for overall, left neck, right neck, and primary tumor site response, respectively. The sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy of the therapy assessment were 68.1%, 92.2%, 71.1%, 91.1%, and 86.9%, respectively. Cox multivariate regression analysis showed human papillomavirus (HPV) status and PET/CT interpretation were the only factors associated with PFS and OS. Among the HPV-positive patients (n = 123), there was a significant difference in PFS (hazard ratio [HR], 0.14; 95% confidence interval, 0.03-0.57; P = 0.0063) and OS (HR, 0.01; 95% confidence interval, 0.00-0.13; P = 0.0006) between the patients who had a score negative for residual tumor versus positive for residual tumor. A similar significant difference was observed in PFS and OS for all patients. There was also a significant difference in the PFS of patients with PET-avid residual disease in one site versus multiple sites in the neck (HR, 0.23; log-rank P = 0.004).

CONCLUSION

The Hopkins 5-point qualitative therapy response interpretation criteria for head and neck PET/CT has substantial interreader agreement and excellent negative predictive value and predicts OS and PFS in patients with HPV-positive HNSCC.

Meeting the challenges of PET-based molecular imaging in cancer

As personalized medicine becomes a reality, there is a need for specific imaging agents that reflect molecular characteristics of a cancer. Fluorodeoxyglucose is an important advance because of its sensitivity. Newer molecular imaging probes offer higher specificity and are categorized as: radiolabeled biomimetics; antibody-antibody fragments and drug-drug-like compounds. Biomimetics have high sensitivity but tend to be less specific as they often engage natural transporters and metabolic pathways. Antibodies and their fragments are specific but may be limited by slow clearance. Labeled drugs and drug-like compounds offer good specificity but may be limited in sensitivity. There are numerous challenges facing molecular imaging related to their complexity. Additionally, fear of ionizing radiation and regulatory constraints have somewhat inhibited clinical translation. However, there is reason for optimism due to economies of scale and a changing health care system, which places a premium on diagnostic accuracy. Although molecular imaging is not likely to become mainstream in the near future, its long-term prospects for doing so are excellent.

Abstract P4-01-09: 18F-FLT-PET/CT for the prediction of response to ANG-1005 therapy in patients with brain metastases from breast cancer

Background: ANG1005 (formerly called GRN1005) is a peptide-drug conjugate being developed for targeted treatment of brain metastases. It consists of 3 molecules of paclitaxel covalently linked to Angiopep-2 designed to cross the blood brain barrier (BBB) via the low density lipoprotein (LDL) receptor-related protein-1 (LRP1)-mediated trancytosis. This drug was evaluated in a multi-center, open-label single-arm study (GRABMB study). An interim analysis determined that the agent met the futility endpoint based on MRI assessment (SABC 2012). However, centrally confirmed responses were achieved in the study, and a biomarker substudy enrolling patients (pts) to evaluate the utility of FLT-PET in assessing response to treatment with ANG1005 suggested sufficient activity of the agent to allow continuation of the study. 18F-FLT (3’-Fluoro-3’ deoxythymidine)-PET imaging is a novel imaging modality which provides a tool for measuring in vivo tumor cell proliferation. FLT is an analog of thymidine; cellular retention of FLT reflects DNA synthesis.

Methods: Adult pts with measurable BMBC were eligible with or without history of prior WBRT. We compared 18F-FLT-PET/CT with MRI-gadolinium contrast images for brain metastases detection and for assessment of whether treatment with ANG1005 was associated with significant change in intracranial tumor uptake of 18F-FLT.

ANG1005 therapy was administered intravenously at 550 mg/m2 q 21d until progression of intra-cranial disease or unacceptable toxicity. All pts underwent 18F-FLT PET/CT imaging before and after 1 cycle of therapy with ANG1005. Pts were scanned dynamically over 30 min followed by a static whole body PET image at 1 hour post-injection. We calculated the% of change before and after therapy, with change &gt; 20% considered significant.

Results: 5/10 planned pts have been accrued to the substudy to date, and 12 metastatic brain lesions have been analyzed. The maximum standard uptake value (SUVmax) ranged from 0.8 to 4.0, mean 1.8 for baseline scans. Tumor to normal brain background ratios ranged from 3.2 to 22.3, mean 9.4. 7/12 lesions showed &gt;20% change between pre and post therapy. The average% change was (-) 42.39% ± 12.77, range: 29.2 to 66.8% (using SUVmax), and (-) 38.7% ± 14.3, range: 20.12 to 57.10% (using tumor to normal ratios). Based on brain MRI evaluation per RECIST 1.1 criteria, 1 pt had intra-cranial partial response (PR) and 3 patients had stable disease (SD). These pts remained on therapy for an average of 7 cycles, range: 5 to 9 cycles. 1 pt withdrew consent after 2 cycles of therapy and opted to receive whole brain radiation therapy. 5/42 pts achieved a confirmed investigator-assessed PR by MRI at 550 mg/m2, and 4/13 pts achieved a PR at 650 mg/m2, a dose not progressed due to toxicity.

Conclusion: This pilot study using 18F-FLT-PET imaging of brain metastases suggests that it is a promising tool for detection and measurement of CNS disease. Given that contrast-enhanced MRI detection of brain metastases represent gadolinium leakage through the BBB rather than actual tumor volume measurements, better approaches are needed to assess efficacy of therapies. Accrual to this study is ongoing. Updated results with ANG1005 will be presented during the meeting.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-01-09.

Comparison of endorectal coil and nonendorectal coil T2W and diffusion-weighted MRI at 3 Tesla for localizing prostate cancer: correlation with whole-mount histopathology

PURPOSE

To compare utility of T2-weighted (T2W) MRI and diffusion-weighted MRI (DWI-MRI) obtained with and without an endorectal coil at 3 Tesla (T) for localizing prostate cancer.

MATERIALS AND METHODS

This Institutional Review Board-approved study included 20 patients (median prostate-specific antigen, 8.4 ng/mL). Patients underwent consecutive prostate MRIs at 3T, first with a surface coil alone, then with combination of surface, endorectal coils (dual coil) followed by robotic assisted radical prostatectomy. Lesions were mapped at time of acquisition on dual-coil T2W, DWI-MRI. To avoid bias, 6 months later nonendorectal coil T2W, DWI-MRI were mapped. Both MRI evaluations were performed by two readers blinded to pathology with differences resolved by consensus. A lesion-based correlation with whole-mount histopathology was performed.

RESULTS

At histopathology 51 cancer foci were present ranging in size from 2 to 60 mm. The sensitivity of the endorectal dual-coil, nonendorectal coil MRIs were 0.76, 0.45, respectively. PPVs for endorectal dual-coil, nonendorectal coil MRI were 0.80, 0.64, respectively. Mean size of detected lesions with nonendorectal coil MRI were larger than those detected by dual-coil MRI (22 mm versus 17.4 mm).

CONCLUSION

Dual-coil prostate MRI detected more cancer foci than nonendorectal coil MRI. While nonendorectal coil MRI is an attractive alternative, physicians performing prostate MRI should be aware of its limitations.

Localized prostate cancer detection with 18F FACBC PET/CT: comparison with MR imaging and histopathologic analysis

PURPOSE

To characterize uptake of 1-amino-3-fluorine 18-fluorocyclobutane-1-carboxylic acid ((18)F FACBC) in patients with localized prostate cancer, benign prostatic hyperplasia (BPH), and normal prostate tissue and to evaluate its potential utility in delineation of intraprostatic cancers in histopathologically confirmed localized prostate cancer in comparison with magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Institutional review board approval and written informed consent were obtained for this HIPAA-compliant prospective study. Twenty-one men underwent dynamic and static abdominopelvic (18)F FACBC combined positron emission tomography (PET) and computed tomography (CT) and multiparametric (MP) 3-T endorectal MR imaging before robotic-assisted prostatectomy. PET/CT and MR images were coregistered by using pelvic bones as fiducial markers; this was followed by manual adjustments. Whole-mount histopathologic specimens were sliced with an MR-based patient-specific mold. (18)F FACBC PET standardized uptake values (SUVs) were compared with those at MR imaging and histopathologic analysis for lesion- and sector-based (20 sectors per patient) analysis. Positive and negative predictive values for each modality were estimated by using generalized estimating equations with logit link function and working independence correlation structure.

RESULTS

(18)F FACBC tumor uptake was rapid but reversible. It peaked 3.6 minutes after injection and reached a relative plateau at 15-20 minutes (SUVmax[15-20min]). Mean prostate tumor SUVmax(15-20min) was significantly higher than that of the normal prostate (4.5 ± 0.5 vs 2.7 ± 0.5) (P < .001); however, it was not significantly different from that of BPH (4.3 ± 0.6) (P = .27). Sector-based comparison with histopathologic analysis, including all tumors, revealed sensitivity and specificity of 67% and 66%, respectively, for (18)F FACBC PET/CT and 73% and 79%, respectively, for T2-weighted MR imaging. (18)F FACBC PET/CT and MP MR imaging were used to localize dominant tumors (sensitivity of 90% for both). Combined (18)F FACBC and MR imaging yielded positive predictive value of 82% for tumor localization, which was higher than that with either modality alone (P < .001).

CONCLUSION

(18)F FACBC PET/CT shows higher uptake in intraprostatic tumor foci than in normal prostate tissue; however, (18)F FACBC uptake in tumors is similar to that in BPH nodules. Thus, it is not specific for prostate cancer. Nevertheless, combined (18)F FACBC PET/CT and T2-weighted MR imaging enable more accurate localization of prostate cancer lesions than either modality alone.

Functional and molecular imaging: applications for diagnosis and staging of localised prostate cancer

Prostate cancer is currently the most common solid organ cancer type among men in the Western world. Currently, all decision-making algorithms and nomograms rely on demographics, clinicopathological data and symptoms. Such an approach can easily miss significant cancers while detecting many insignificant cancers. In this review, novel functional and molecular imaging techniques used in the diagnosis and staging of localised prostate cancer and their effect on treatment decisions are discussed.

Developing a molecular imaging agent for Met using onartuzumab (MetMAb)

11083

Background: Developing an imaging agent to assess Met expression would aid in diagnosis and monitoring tumor response to Met-targeted therapies. Onartuzumab (MetMAb), a Met selective humanized one-armed monoclonal antibody, has been studied in Phase I-II clinical trials in which it was generally well tolerated and has shown the most benefit in patients with MET positive tumors. Methods: Studies to assess Met-binding were executed using the human gastric carcinoma cell line MKN-45 which exhibits a high level of Met expression. Murine PET studies and biodistribution assays were performed using MKN-45 xenografts. Results: Plasma shed Met concentration is directly related to total tumor burden (p < 0.001). The absence of a positive correlation between shed Met and %ID in blood indicates that binding of tracer to shed Met present in plasma is unlikely. There are positive correlations between tumor mass, Met abundance, and phosphoMet content and uptake of 89Zr-df-onartuzumab in MKN-45 mouse xenografts. Lastly, tumor mass, Met, pMet and 89Zr-df-onartuzumab uptake were all significantly decreased by drug treatment. Conclusions: MKN-45 tumor uptake of 89Zr-df-onartuzumab correlated significantly with tumor mass and Met abundance. Blood tracer uptake did not positively correlate with the presence of plasma shed Met. The amounts of Met, pMet, as well as 89Zr-df-onartuzumab image intensity correlated significantly with tumor size (all Spearman p values < 0.001).Tumor volumes and Met content were significantly decreased in TKI treated versus control mice, which correlated with imaging results.89Zr-df-onartuzumab has potential utility for imaging Met to identify patients for treatment with Met-targeted therapeutics and to identify the emergence of Met-driven acquired resistance to other molecularly targeted cancer therapies.

Abstract 369: Role of bone marrow angiogenesis in myeloma and its precursor disease: a prospective clinical trial

Background: Based on bone marrow (BM) biopsies, increased angiogenesis has been reported in multiple myeloma (MM) and smoldering multiple myeloma (SMM) patients compared with individuals with monoclonal gammopathy of undetermined significance (MGUS). In this prospective clinical trial open for MGUS, SMM and MM patients, we conducted BM biopsies and used immunohistochemistry to define microvessel density (MVD) in every patient; results were compared to results obtained from dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and multiplex ELISA-based serum angiogenic cytokine assays.

Patients and Methods: We included 10 MGUS, 10 SMM and 10 MM patients. We performed DCE-MRI of entire lumbosacral spine to compare exchange rate constants (contrast agent transit from the extravascular compartment to the intravascular compartment, Kep; movement of contrast agent from plasma to extravascular extracellular space, Ktrans) with bone marrow biopsies immunostained with CD34 as measures of MVD, and serum angiogenic markers By ELISA to include EGF, Ang2, GCSF, BMP9, endoglin, Leptin, Follistatin, IL8, HGF, HBEGF, PLGF, VEGFC, VEGFD, FGF2, VEGFA. The association among continous parameters was determined by Spearman rank correlation. Trends in continuous parameters according to ordered categorical parameter were determined by Jonckheere-Terpstra test for trend. The parameters between two groups were compared using an exact Wilcoxon rank sum test.

Results: Both MVD and Kep increased along the myeloma spectrum (MGUS &lt; SMM &lt; MM). MVD and Kep were strongly correlated (r=0.93 and p=0.002). Ktrans was weakly to moderately well correlated with MVD (r=0.43 p=0.03). Higher Kep values were seen in MM/SMM vs. MGUS patients (median 7.1 vs. 3.9; p=0.08). Similarly, higher MVD values were seen in MM/SMM patients versus MGUS (median 20 vs. 15; p=0.01). As regards serum angiogenic markers, levels of HGF (r=0.45; p=0.02), Ang2(r=0.37 and p=0.06), and VEGFD (r=-0.35 and p=0.07), correlated with Kep. The levels of Ang2 (p=0.02), GCSF (p=0.06), follistatin (p=0.06), HGF (p=0.01), and VEGFA (p=0.02), were elevated in MM/SMM patients in comparison to MGUS. Other angiogenic cytokines did not correlate with MVD or Kep.

Conclusions: MVD and Kep (measured by DCE-MRI) were highly statistically correlated. MVD increased along the disease spectrum from MGUS to SMM to MM (p=0.008). Some, but not all, angiogenic biomarkers detected in peripheral blood were associated with increased vascularity in the bone marrow.

Citation Format: Manisha Bhutani, Esther Mena, Irina Maric, Esther Tan, Neha Korde, Alexandra R. Berg, Alex R. Minter, Brendan M. Weiss, Liza Lindenberg, Baris Turkbey, Omer Aras, Seth Steinberg, Troy Kemp, Katherine R. Calvo, Peter L. Choyke, Karen Kurdziel, Ola Landgren. Role of bone marrow angiogenesis in myeloma and its precursor disease: a prospective clinical trial. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 369. doi:10.1158/1538-7445.AM2013-369

18F-fluorodeoxyglucose positron emission tomography in the management of patients with thymic epithelial tumors

PURPOSE

There are limited data regarding the role of (18)F-fluorodeoxyglucose positron emission tomography ([(18)F]-FDG PET) imaging in management of patients with thymic epithelial tumors (TET). The primary objective of this study was to assess the usefulness of early [(18)F]-FDG PET to monitor treatment efficacy and its correlation with Response Evaluation Criteria in Solid Tumors (RECIST) in patients with TETs.

EXPERIMENTAL DESIGN

[(18)F]-FDG PET/computed tomographic (CT) scans were conducted at baseline and after 6 weeks of treatment in patients enrolled in two phase II and one phase I/II clinical trials. On the basis of data from other solid tumors, metabolic response was defined as a reduction of [(18)F]-FDG uptake by more than 30% as assessed by average standardized uptake values (SUV) of up to five most metabolically active lesions.

RESULTS

Fifty-six patients with unresectable Masaoka stage III or IV TETs were included. There was a close correlation between early metabolic response and subsequent best response using RECIST (P < 0.0001-0.0003): sensitivity and specificity for prediction of best response were 95% and 100%, respectively. Metabolic responders had significantly longer progression-free survival (median, 11.5 vs. 4.6 months; P = 0.044) and a trend toward longer overall survival (median, 31.8 vs. 18.4 months; P = 0.14) than nonresponders. [(18)F]-FDG uptake was significantly higher in thymic carcinoma than in thymoma (P = 0.0004-0.0010).

CONCLUSION

In patients with advanced TETs, early metabolic response closely correlates with outcome of therapy. [(18)F]-FDG PET may be used to monitor treatment efficacy and assess histologic differences in patients with advanced TETs.