Assessment of recurrent colorectal cancer following 5-fluorouracil chemotherapy using both 18FDG and 18FLT PET

Combined imaging biomarkers for therapy evaluation in glioblastoma multiforme: correlating sodium MRI and F-18 FLT PET on a voxel-wise basis

We evaluate novel magnetic resonance imaging (MRI) and positron emission tomography (PET) quantitative imaging biomarkers and associated multimodality, serial-time-point analysis methodologies, with the ultimate aim of providing clinically feasible, predictive measures for early assessment of response to cancer therapy. A focus of this work is method development and an investigation of the relationship between the information content of the two modalities. Imaging studies were conducted on subjects who were enrolled in glioblastoma multiforme (GBM) therapeutic clinical trials. Data were acquired, analyzed and displayed using methods that could be adapted for clinical use. Subjects underwent dynamic [(18)F]fluorothymidine (F-18 FLT) PET, sodium ((23)Na) MRI and 3-T structural MRI scans at baseline (before initiation of therapy), at an early time point after beginning therapy and at a late follow-up time point after therapy. Sodium MRI and F-18 FLT PET images were registered to the structural MRI. F-18 FLT PET tracer distribution volumes and sodium MRI concentrations were calculated on a voxel-wise basis to address the heterogeneity of tumor physiology. Changes in, and differences between, these quantities as a function of scan timing were tracked. While both modalities independently show a change in tissue status as a function of scan time point, results illustrate that the two modalities may provide complementary information regarding tumor progression and response. Additionally, tumor status changes were found to vary in different regions of tumor. The degree to which these methods are useful for GBM therapy response assessment and particularly for differentiating true progression from pseudoprogression requires additional patient data and correlation of these imaging biomarker changes with clinical outcome.

Gemcitabine alone or in combination with cisplatin in patients with advanced or metastatic cholangiocarcinomas or other biliary tract tumours: a multicentre randomised phase II study - The UK ABC-01 Study

BACKGROUND

We assessed the activity of gemcitabine (G) and cisplatin/gemcitabine (C/G) in patients with locally advanced (LA) or metastatic (M) (advanced) biliary cancers (ABC) for whom there is no standard chemotherapy.

METHODS

Patients, aged > or =18 years, with pathologically confirmed ABC, Karnofsky performance (KP) > or =60, and adequate haematological, hepatic and renal function were randomised to G 1000 mg m(-2) on D1, 8, 15 q28d (Arm A) or C 25 mg m(-2) followed by G 1000 mg m(-2) D1, 8 q21d (Arm B) for up to 6 months or disease progression.

RESULTS

In total, 86 patients (A/B, n=44/42) were randomised between February 2002 and May 2004. Median age (64/62.5 years), KP, primary tumour site, earlier surgery, indwelling biliary stent and disease stage (LA: 25/38%) are comparable between treatment arms. Grade 3-4 toxicity included (A/B, % patients) anaemia (4.5/2.4), leukopenia (6.8/4.8), neutropenia (13.6/14.3), thrombocytopenia (9.1/11.9), lethargy (9.1/28.6), nausea/vomiting (0/7.1) and anorexia (2.3/4.8). Responses (WHO criteria, % of evaluable patients: A n=31 vs B n=36): no CRs; PR 22.6 vs 27.8%; SD 35.5 vs 47.1% for a tumour control rate (CR+PR+SD) of 58.0 vs 75.0%. The median TTP and 6-month progression-free survival (PFS) (the primary end point) were greater in the C/G arm (4.0 vs 8.0 months and 45.5 vs 57.1% in arms A and B, respectively).

CONCLUSION

Both regimens seem active in ABC. C/G is associated with an improved tumour control rate, TTP and 6-month PFS. The study has been extended (ABC-02 study) and powered to determine the effect on overall survival and the quality of life.

(18)F-FDG and (18)F-FLT uptake early after cyclophosphamide and mTOR inhibition in an experimental lymphoma model

To be a reliable predictor of response, tracer uptake should reflect changes in the amount of active tumor cells. However, uptake of (18)F-FDG, the most commonly used PET tracer, is disturbed by the inflammatory cells that appear early after cytotoxic therapy. The first aim of this study was to investigate whether 3'-(18)F-fluoro-3'-deoxy-l-thymidine ((18)F-FLT), a marker of cellular proliferation, is a better tracer for response assessment early after cytotoxic therapy. A second objective of this study was to investigate whether (18)F-FDG and (18)F-FLT responses were comparable early after mammalian target of rapamycin (mTOR) inhibition, as an example of proliferation-targeting therapies.

METHODS

Severe combined immunodeficient mice were subcutaneously inoculated with Granta-519 cells, a human cell line derived from a leukemic mantle cell lymphoma. Half the mice were treated with cyclophosphamide and the other half with mTOR inhibition. (18)F-FDG and (18)F-FLT uptake was evaluated by small-animal PET on day 0 (D0; before treatment), D+1, D+2, D+4, D+7, D+9, D+11, and D+14. At each time point, 2 mice of each treatment condition were sacrificed, and tumors were excised for histopathology.

RESULTS

After cyclophosphamide, (18)F-FDG and (18)F-FLT uptake decreased, with a maximum reduction of -29% for (18)F-FDG and -25% for (18)F-FLT uptake at D+2, compared with baseline. Although (18)F-FDG uptake increased from D+4 on, with a maximum on D+7, (18)F-FLT uptake remained virtually stable. Histology showed an increase in apoptotic or necrotic tumor fraction, followed by an influx of inflammatory cells. In mTOR-inhibited mice, (18)F-FDG uptake dropped until D+2 after therapy (-43%) but increased at D+4 (-27%) to form a plateau on D+7 and D+9 (-14% and -16%, respectively). Concurrently, (18)F-FLT uptake decreased to -31% on D+2, followed by an increase with a peak value of +12% on D+7, after which (18)F-FLT uptake decreased again. Cyclin D1 expression dropped from D+1 until D+4 and returned to baseline at D+7.

CONCLUSION

Because (18)F-FLT uptake is not significantly influenced by the temporary rise in inflammatory cells early after cyclophosphamide, it more accurately reflects tumor response. However, a formerly unknown temporary rise in (18)F-FLT uptake a few days after the administration of mTOR inhibition was defined, which makes it clear that drug-specific responses have to be considered when using PET for early treatment monitoring.

Conventional and novel PET tracers for imaging in oncology in the era of molecular therapy

In the last ten years, the development of several novel targeted drugs and the refinement of state of the art technologies such as the genomics and proteomics and their introduction to clinical practice have revolutionized the management of patients affected by cancer. However, everyday practice points out several clinical questions: the difficulty of response assessment to new drugs especially using standard RECIST criteria that do not provide information on biological, vascular or metabolic variations; the inadequate selection of patients who are likely to benefit from a targeted therapy excluding those with breast cancer and gastrointestinal stromal tumours; the need to know the global biological background of diseases especially in metastatic setting using repeatable non-invasive procedures. Molecular imaging could provide information on in vivo distribution of biological markers in response to targeted therapy and could improve the selection of patients before therapies. The aim of this review is to analyze the current role of conventional and innovative positron emission tomography (PET) radiotracers in clinical practice and to explore the promising perspectives of molecular imaging in cancer research.

18F-fluorothymidine kinetics of malignant brain tumors

PURPOSE

18F-labeled deoxy-fluorothymidine (FLT), a marker of cellular proliferation, has been used in PET tumor imaging. Here, the FLT kinetics of malignant brain tumors were investigated.

METHODS

Seven patients with high-grade tumors and two patients with metastases had 12 studies. After 1.5 MBq/kg 18F-FLT had been administered intravenously, dynamic PET studies were acquired for 75 min. Images were reconstructed with iterative algorithms, and corrections applied for attenuation and scatter. Parametric images were generated with factor analysis, and vascular input and tumor output functions were derived. Compartmental models were used to estimate the rate constants.

RESULTS

The standard three-compartment model appeared appropriate to describe 18F-FLT uptake. Corrections for blood volume, metabolites, and partial volume were necessary. Kinetic parameters were correlated with tumor pathology and clinical follow-up data. Two groups could be distinguished: lesions that were tumor predominant (TumP) and lesions that were treatment change predominant (TrcP). Both groups had a widely varying k1 (transport across the damaged BBB, range 0.02-0.2). Group TrcP had a relatively low k3 (phosphorylation rate, range 0.017-0.027), whereas k3 varied sevenfold in group TumP (range 0.015-0.11); the k3 differences were significant (p < 0.01). The fraction of transported FLT that is phosphorylated [k3/(k2+k3)] was able to separate the two groups (p < 0.001).

CONCLUSION

A three-compartment model with blood volume, metabolite, and partial volume corrections could adequately describe 18F-FLT kinetics in malignant brain tumors. Patients could be distinguished as having: (1) tumor-predominant or (2) treatment change-predominant lesions, with significantly different phosphorylation rates.

The contribution of PET/CT to improved patient management

With the introduction of both SPET/CT and PET/CT, multimodality imaging has truly entered routine clinical practice. Multiple slice spiral CT scanners have been incorporated with multiple detector gamma cameras or PET systems, such that the benefit of these modalities can be achieved in one patient sitting. The subject of this manuscript is PET/CT and its impact on patient management. Applications of PET/CT span the whole field of medical and surgical oncology since very few cancers do not take up the labelled glucose tracer, (18)F-FDG. Given the contrast achieved, high-quality data can be obtained with FDG PET/CT. This technology has now spread worldwide and has been the subject of intense interest, as witnessed by the vast body of published evidence. In this short overview, only a brief discussion of the main clinical applications is possible. Novel applications of PET/CT outside the field of oncology are expected in the near future.

How often do patients undergo repeat PET or PET/CT examinations? Experience from a UK institution

BACKGROUND AND AIM

According to the report of the Intercollegiate Standing Committee on Nuclear Medicine, the UK requires 40-60 positron emission tomography (PET) machines in the next decade (Intercollegiate Standing Committee on Nuclear Medicine). Positron Emission Tomography: a Strategy for Provision in the UK. London: Royal College of Physicians of London; 2003, pp. 1-9). This figure is based mainly on patients receiving only one examination and restricting the clinical indication to three primary diagnoses. The aim of this study was to assess the appropriateness of this figure and the assumptions made in the Intercollegiate report on UK PET provision.

METHODS

We examined retrospectively our institution's entire PET and PET/computed tomography (CT) database, which spans 4 years and 9 months. We recorded the number of patients who received repeat examinations.

RESULTS

Reports were available for 3354 PET/CT or PET-only studies; 418 of 2268 patients (18.4%) received at least one repeat PET/CT examination. The three main indications for PET examination in the Intercollegiate report only accounted for approximately 60% of the examinations undertaken.

CONCLUSION

Our records suggest that basing the UK's future PET provision on a single examination and on three clinical indications only is no longer realistic.

Clinical relevance of imaging proliferative activity in lung nodules

PURPOSE

Recently, the thymidine analogue 3'-deoxy-3'[18F]fluorothymidine (FLT) has been introduced for imaging proliferation with positron emission tomography (PET). In this prospective study, we examined the accuracy of FLT for differentiation of benign from malignant lung lesions and for tumour staging.

METHODS

A total of 47 patients with newly diagnosed pulmonary nodules on chest CT suspicious for malignancy were examined with FLT-PET in addition to routine staging procedures. A total of 43 patients also underwent 2-[18F]fluoro-2-deoxy-D-glucose (FDG) PET imaging. Within 2 weeks, patients underwent resective surgery or core biopsy of the pulmonary lesion.

RESULTS

Histopathology revealed malignant lung tumours in 32 patients (20 non-small cell lung cancer, 1 small cell lung cancer, 1 pulmonary carcinoid, 1 non-Hodgkin's lymphoma, nine metastases from extrapulmonary tumours) and benign lesions in 15 patients. Increased FLT uptake was exclusively related to malignant tumours. FLT-PET was false negative in two patients with non-small cell lung cancer, in the patient with a pulmonary carcinoid and in three patients with lung metastases. The sensitivity of FLT-PET for detection of lung cancer was 90%, the specificity 100% and the accuracy 94%. Fifteen out of 21 patients with lung cancer had mediastinal lymph node metastases. FLT-PET was true positive in 7/15 patients, resulting in a sensitivity of 53% for N-staging (specificity 100%, accuracy 67%). Clinical TNM stage was correctly identified in 67% (20/30) patients, compared to 85% (23/27) with FDG-PET.

CONCLUSION

FLT-PET has a high specificity for the detection of malignant lung tumours. Compared with FDG, FLT-PET is less accurate for N-staging in patients with lung cancer and for detection of lung metastases. FLT-PET therefore cannot be recommended for staging of lung cancer.

PET imaging in assessing gastrointestinal tumors

The clinical usefulness of FDG-PET imaging is now firmly established in various situations, such as the preoperative staging of esophageal cancer and recurrent colorectal carcinoma and the detection and staging of recurrent colorectal cancer when there is a clinical or biologic suspicion with inconclusive conventional findings. Encouraging results were obtained in the evaluation of the therapeutic response of various gastrointestinal malignancies, either during the treatment or after its completion. There is no firm consensus regarding its role in pancreatic cancer, either proved or suspected, but it may be valuable in selected clinical situations. Its role seems fairly limited in patients with hepatocellular carcinoma, although PET findings may have prognostic implications. Evaluation of cholangiocarcinoma is an emerging indication, albeit with limited data to date. Finally, PET/CT is very likely to enhance the role of FDG imaging further in the work-up of patients with gastrointestinal tumors.