Cerenkov Luminescence Imaging as a Modality to Evaluate Antibody-Based PET Radiotracers.

Antibodies, and engineered antibody fragments, labeled with radioisotopes are being developed as radiotracers for the detection and phenotyping of diseases such as cancer. The development of antibody-based radiotracers requires extensive characterization of their in vitro and in vivo properties, including their ability to target tumors in an antigen-selective manner. In this study, we investigated the use of Cerenkov luminescence imaging (CLI) as compared with PET as a modality for evaluating the in vivo behavior of antibody-based radiotracers. METHODS: The anti-prostate-specific membrane antigen (PSMA) huJ591 antibody (IgG; 150 kDa) and its minibody (Mb; 80 kDa) format were functionalized with the chelator 1,4,7-triazacyclononane-1-glutaric acid-4,7-diacetic acid (NODAGA) and radiolabeled with the positron-emitting radionuclide 64Cu (half-life, 12.7 h). Immunoreactive preparations of the radiolabeled antibodies were injected into NCr nu/nu mice harboring PSMA-positive CWR22Rv1 and PSMA-negative PC-3 tumor xenografts. Tumor targeting was evaluated by both PET and CLI. RESULTS: 64Cu-NODAGA-PSMA-IgG and 64Cu-NODAGA-PSMA-Mb retained the ability to bind cell surface PSMA, and both radiotracers exhibited selective uptake into PSMA-positive tumors. Under the experimental conditions used, PSMA-selective uptake of 64Cu-NODAGA-PSMA-IgG and 64Cu-NODAGA-PSMA-Mb was observed by CLI as early as 3 h after injection, with tumor-to-background ratios peaking at 24 (IgG) and 16 (Mb) h after injection. Targeting data generated by CLI correlated with that generated by PET and necropsy. CONCLUSION: CLI provided a rapid and simple assessment of the targeting specificity and pharmacokinetics of the antibody-based PET radiotracers that correlated well with the behavior observed by standard PET imaging. Moreover, CLI provided clear discrimination between uptake kinetics of an intact IgG and its small-molecular-weight derivative Mb. These data support the use of CLI for the evaluation of radiotracer performance.

Extranodal extension of metastatic papillary thyroid carcinoma: correlation with biochemical endpoints, nodal persistence, and systemic disease progression.

BACKGROUND: The impact of extranodal extension (ENE) of metastatic papillary thyroid carcinoma (PTC) on short- and long-term clinical outcomes, including biochemical testing, has not been reported. METHODS: This single-institution National Cancer Institute-designated Comprehensive Cancer Center cohort study included patients with macroscopic metastases and excluded patients with gross residual disease after surgery, distant disease, or poorly differentiated papillary carcinoma. A suppressed or stimulated thyroglobulin (Tg) < 1 ng/mL, without suspicious imaging or anti-thyroglobulin antibodies, after radioactive iodine (RAI) treatment was termed an excellent or "complete biochemical response" (CR). RESULTS: Of 89 subjects included, 60 previously untreated patients underwent total thyroidectomy and therapeutic neck dissection; 29 additional patients underwent a neck dissection for persistence or recurrence after prior surgery and RAI administration. ENE, identified in 29 patients (33%), was associated with T4 classification (p = 0.02) and involvement of a greater number of nodes (median 11 vs. 5, p = 0.03). ENE was associated with a 20% increased risk of nodal persistence necessitating additional surgery (p = 0.02). In a multivariable analysis, ENE, T4 classification, and recurrence/persistence proved to be independent predictors of systemic disease progression (ENE: hazard ratio [HR] 4.3 [95% confidence interval (CI) 1.2-15], p = 0.02; T4 classification: HR 4.2 [CI 1.3-14], p = 0.01; recurrent/persistent status: HR 3.6 [CI 1.1-12], p = 0.035). Nodal or systemic disease progression was rare after a biochemical CR; in contrast, in previously untreated patients, stimulated Tg levels (sTg) > 50 ng/mL prior to initial RAI administration, heralded the progression of nodal disease, and also predicted the eventual development of systemic disease (p = 0.0001). Of those with a sTg > 50 ng/mL, over 70% underwent surgery for nodal persistence within five years. The presence of ENE diminished the odds of a biochemical CR (odds ratio 3.5% [CI 1.3-10], p = 0.02), and increased the probability that the sTg levels after surgery will exceed 50 ng/mL (odds ratio 5 [CI 1.2-21], p = 0.03). Following surgery for tumor persistence, 25% of those with ENE were rendered biochemically free of disease. CONCLUSIONS: ENE diminishes the probability of a biochemical CR after treatment for regional metastatic PTC, and increases the probability of tumor persistence after initial resection, likely from abundant metastasis. ENE and nodal persistence independently predict eventual systemic disease progression.

Predicting pathological response to neoadjuvant chemoradiotherapy in locally advanced rectal cancer using 18FDG-PET/CT.

BACKGROUND: Pathologic complete response (pCR) after neoadjuvant chemoradiation (CRT) has been observed in 15-30% of patients with locally advanced rectal cancer (LARC). The objective of this study was to determine whether PET/CT can predict pCR and disease-free survival in patients receiving CRT with LARC. METHODS: This is a retrospective review of patients with EUS-staged T3-T4, N+rectal tumors treated with CRT, who underwent pre/post-treatment PET/CT from 2002-2009. All patients were treated with CRT and surgical resection. Standardized uptake value (SUV) of each tumor was recorded. Logistic regression was used to analyze the association of pre-CRT SUV, post-CRT SUV, %SUV change, and time between CRT and surgery, compared with pCR. Kaplan-Meier estimation evaluated significant predictors of survival. RESULTS: Seventy patients (age 62 years; 42M:28F) with preoperative stage T3 (n=61) and T4 (n=9) underwent pre- and post-CRT PET/CT followed by surgery. The pCR rate was 26%. Median pre-CRT SUV was 10.8, whereas the median post-CRT SUV was 4 (P=0.001). Patients with pCR had a lower median post-CRT SUV compared with those without (2.7 vs. 4.5, P=0.01). Median SUV decrease was 63% (7.5-95.5%) and predicted pCR (P=0.002). Patients with a pCR had a greater time interval between CRT and surgery (median, 58 vs. 50 days) than those without (P=0.02). Patients with post-CRT SUV<4 had a lower recurrence compared with those without (P=0.03). Patients with SUV decrease≥63% had improved overall survival at median follow-up of 40 months than those without (P=0.006). CONCLUSIONS: PET/CT can predict response to CRT in patients with LARC. Posttreatment SUV, %SUV decrease, and greater time from CRT to surgery correlate with pCR. Post-CRT, SUV<4, and SUV decrease≥63% were predictive of recurrence-free and overall survival.

Use of molecular imaging to predict clinical outcome in patients with rectal cancer after preoperative chemotherapy and radiation.

PURPOSE: To correlate changes in 2-deoxy-2-[18F]fluoro-d-glucose (18-FDG) positron emission tomography (PET) (18-FDG-PET) uptake with response and disease-free survival with combined modality neoadjuvant therapy in patients with locally advanced rectal cancer. METHODS AND MATERIALS: Charts were reviewed for consecutive patients with ultrasound-staged T3x to T4Nx or TxN1 rectal adenocarcinoma who underwent preoperative chemoradiation therapy at Fox Chase Cancer Center (FCCC) or Robert H. Lurie Comprehensive Cancer Center of Northwestern University with 18-FDG-PET scanning before and after combined-modality neoadjuvant chemoradiation therapy . The maximum standardized uptake value (SUV) was measured from the tumor before and 3 to 4 weeks after completion of chemoradiation therapy preoperatively. Logistic regression was used to analyze the association of pretreatment SUV, posttreatment SUV, and % SUV decrease on pathologic complete response (pCR), and a Cox model was fitted to analyze disease-free survival. RESULTS: A total of 53 patients (FCCC, n = 41, RLCCC, n = 12) underwent pre- and postchemoradiation PET scanning between September 2000 and June 2006. The pCR rate was 31%. Univariate analysis revealed that % SUV decrease showed a marginally trend in predicting pCR (p = 0.08). In the multivariable analysis, posttreatment SUV was shown a predictor of pCR (p = 0.07), but the test results did not reach statistical significance. None of the investigated variables were predictive of disease-free survival. CONCLUSIONS: A trend was observed for % SUV decrease and posttreatment SUV predicting pCR in patients with rectal cancer treated with preoperative chemoradiation therapy. Further prospective study with a larger sample size is warranted to better characterize the role of 18-FDG-PET for response prediction in patients with rectal cancer.