18F-FLT and 18F-FDG positron emission tomography for the imaging of advanced well-differentiated gastro-entero-pancreatic endocrine tumours

18F-FLT PET/CT imaging for early monitoring response to CDK4/6 inhibitor therapy in triple negative breast cancer

PURPOSE

Our study was to investigate 18F-FLT PET/CT imaging monitor the early response of CDK4/6 inhibitor therapy in triple negative breast cancer (TNBC).

METHODS

MDA-MB-231 and MDA-MB-468 cell lines and corresponding subcutaneous tumor models in CB17-SCID mice were used. Cell viability assay, cell-cycle analysis, and western blotting were performed in vitro experiments. 18F-FLT PET/CT imaging was performed and the value of tumor/muscle (T/M) of mice was measured before and 1-3 days after treatment in vivo experiments. Then, the tumor volume was recorded every day for 15 days.

RESULTS

In the presence of Palbociclib (CDK4/6 inhibitor), the results of in vitro experiments showed that protein pRB and E2F levels were significantly down-regulated in MDA-MB-231 cells leading to G0/G1 arrest with consumption in S phase compared with MDA-MB-468 cells. In PET/CT imaging, the 18F-FLT T/M ratio of treatment group was a significant and sustained reduction from 1 to 3 days (all p < 0.05) compared with control group in MDA-MB-231 section. However, there was no significant difference between treatment and control groups in MDA-MB-468 section. Compared with the control group, the tumor volume of the treatment group was significantly reduced from the 11th day in MDA-MB-231 section, but not in MDA-MB-468 section until 15 days.

CONCLUSION

18F-FLT PET/CT imaging can immediately and effectively monitor the early treatment response of CDK4/6 inhibitors in TNBC.

18F-FLT PET imaging of cellular proliferation in pancreatic cancer

Pancreatic ductal adenocarcinoma is known for its poor prognosis. Since the development of computerized tomography, magnetic resonance and endoscopic ultrasound, novel imaging techniques have struggled to get established in the management of patients diagnosed with pancreatic adenocarcinoma for several reasons. Thus, imaging assessment of pancreatic cancer remains a field with scope for further improvement. In contrast to cross-sectional anatomical imaging methods, molecular imaging modalities such as positron emission tomography (PET) can provide information on tumour function. Particularly, tumour proliferation may be assessed by measurement of intracellular thymidine kinase 1 (TK1) activity level using thymidine analogues radiolabelled with a positron emitter for use with PET. This approach, has been widely explored with [(18)F]-fluoro-3'-deoxy-3'-L-fluorothymidine ((18)F-FLT) PET. This manuscript reviews the rationale and physiology behind (18)F-FLT PET imaging, with special focus on pancreatic cancer and other gastrointestinal malignancies. Potential benefit and challenges of this imaging technique for diagnosis, staging and assessment of treatment response in abdominal malignancies are discussed.

18F-FLT PET/CT in the Evaluation of Pheochromocytomas and Paragangliomas: A Pilot Study

(18)F-FDG PET/CT has been proven to be a highly sensitive method for pheochromocytomas/paragangliomas (PHEOs/PGLs) associated with succinate dehydrogenase (SDH) mutations. This finding has been attributed to altered tumor cell metabolism resulting from these mutations and does not provide additional prognostic information to genotype. Therefore, identification of new biomarkers for aggressiveness is needed. A high Ki-67 index was proposed to be an additional prognostic factor. This pilot study aimed to evaluate 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) PET/CT, a PET proliferation tracer, as a potential imaging agent in a series of 12 PHEO/PGL patients with different genetic backgrounds, to compare (18)F-FLT uptake with (18)F-FDG PET/CT, and to evaluate classic factors of aggressiveness.

METHODS

Twelve patients (7 metastatic and 5 nonmetastatic) were prospectively evaluated with (18)F-FDG and (18)F-FLT and followed for at least 2 y after the initial imaging work-up. Uptake was assessed at a lesion level, visually and quantitatively by maximum standardized uptake values (SUVmax) for both tracers. (18)F-FLT uptake was compared with risk factors known to be linked with a poor prognosis in PGLs (SDHB-mutated status, lesion size, dopaminergic phenotype) and with (18)F-FDG uptake.

RESULTS

In 12 patients, 77 lesions were assessed. All lesions had low (18)F-FLT uptake (median SUVmax, 2.25; range, 0.7-4.5). There was no apparent superiority of (18)F-FLT uptake in progressive lesions, and most of the lesions showed a mismatch, with high (18)F-FDG uptake (median SUVmax, 10.8; range, 1.1-79.0) contrasting with low (18)F-FLT uptake.

CONCLUSION

This study suggests that PHEOs/PGLs-even those that progress-do not exhibit intense (18)F-FLT uptake. It provides the first in vivo demonstration that proliferation may not be a major determinant of (18)F-FDG uptake in these tumors. These findings provide new insight into the biologic behavior of PGL and suggest that antiproliferative agents may be suboptimal for treatment of these tumors.

Lymphoma as a second malignancy in a patient with neuroendocrine tumor: mimicking dedifferentiation on dual-tracer PET/CT with 68Ga-DOTANOC and 18F-FDG

Neuroendocrine tumors (NETs) are rare tumors which express somatostatin receptors (SSTRs). We here present a case of a 50-year-old female patient with metastatic bronchial carcinoid. She underwent 68Ga-DOTANOC PET/CT and 18F-FDG PET/CT which suggested a diagnosis of poorly differentiated NET. Biopsy of the lesion, however, revealed a second malignancy in the form of diffuse large B-cell lymphoma. Thus, very rarely, other primary tumors can mimic NETs on dual-tracer PET/CT, and biopsy is advised in doubtful cases.

A prospective multicenter phase II study of sunitinib in patients with advanced aggressive fibromatosis

Several studies have reported that imatinib may induce tumor responses and prolonged disease stabilization in aggressive fibromatosis (AF). This effect may relate to the PDGFR-β pathway and KIT mutations. Sunitinib not only inhibits PDGFRs, KIT, and FLT3, it also blocks VEGFRs and thus serves as an antiangiogenic agent. The aim of this prospective multicenter uncontrolled study was to evaluate the efficacy and safety of sunitinib in patients with advanced AF. Nineteen patients with pathologically proven AF were recruited between June, 2008, and March, 2012, from three centers. One treatment cycle consisted of 37.5 mg/day sunitinib for 4 weeks without a break. The primary endpoint was tumor response rate according to RECIST 1.0. Ten (53 %) patients were female and the median age was 30 years (range, 22-67). Most of the primary sites were intra-abdominal (12, 63.2 %), and AF associated with familial adenomatous polyposis in ten patients (52.6 %). With a median of six cycles per patients (range, 1-47 cycles), five patients (26.3 %) achieved a partial response and eight (42.1 %) had stable disease. The overall response rate was 26.3 % (95 % confidence interval [CI], 6.3-45.7) in intention-to-treat analysis. With a median follow-up time of 20.3 months (range, 1.8-50.7), the 2-year rates of progression-free and overall survival were 74.7 % and 94.4 %, respectively. Grade 3 or 4 adverse events of sunitinib that occurred in >5 % of patients were neutropenia (33.3 %), diarrhea (5.3 %), and hand-foot syndrome (5.3 %). In 3 of 12 patients with mesenteric AF, mesenteric mass bleeding (n = 1), bowel perforation (n = 1), and bowel fistula (n = 1) with tumor mass necrosis were observed early during sunitinib treatment. Therefore, sunitinib showed potential antitumor activity and may be useful for the management of non-mesenteric AF.

[Neuroendocrine carcinoma of the digestive tract: a literature review]

Neuroendocrine carcinoma is a rare and agressive malignant tumor, mainly developing at the expense of the respiratory and of the digestive tract. Among the digestive tract, appendix, small bowel, and pancreas are the preferential sites of involvement, other locations have been more rarely reported. Neuroendocrine digestive tumors may present with various symptoms in relationship with their localization and a complex pathophysiology. Diagnosis is often made at an advanced stage, explaining partly the bad prognosis of these tumors. The optimal management of digestive neuroendocrine tumors is rendered difficult by their rarity and by a low number of randomized trials. We review the literature regarding epidemiologic and prognostic features of these rare tumors, their diagnostic and therapeutic care. Potential complications are also discussed.

PET imaging of proliferation with pyrimidines

Several new tracers are being developed for use with PET to assess pathways that are altered in cancers, including energy use, cellular signaling, transport, and proliferation. Because increased proliferation is a hallmark of many cancers, several tracers have been tested to track the DNA synthesis pathway. Thymidine, which is incorporated into DNA but not RNA, has been used in laboratory studies to measure tumor growth. Because thymidine labeled with (11)C undergoes rapid biologic degradation and has a short physical half-life, tracers labeled with (18)F have been preferred in PET imaging. One such tracer is (18)F-labeled 3'-deoxy-3'-fluorothymidine ((18)F-FLT). (18)F-FLT is trapped after phosphorylation by thymidine kinase 1, whose expression is increased in replicating cells. Several studies on breast, lung, and brain tumors have demonstrated that retention of (18)F-FLT correlated with tumor proliferation. Although (18)F-FLT has been used to image and stage several tumor types, the standardized uptake value is generally lower than that obtained with (18)F-FDG. (18)F-FLT can be used to image many areas of the body, but background uptake is high in the liver, marrow, and renal system, limiting use in these organs. (18)F-FLT PET imaging has primarily been studied in the assessment of treatment response. Rapid declines in (18)F-FLT retention within days to weeks have been demonstrated in several tumor types treated with cytotoxic drugs, targeted agents, and radiotherapy. Further work is ongoing to validate this approach and determine its utility in the development of new drugs and in the clinical evaluation of standard treatment approaches.

Diagnostic and prognostic application of positron emission tomography in breast imaging: emerging uses and the role of PET in monitoring treatment response

Positron emission tomography (PET) is an imaging modality that using radiotracers, permits real-time dynamic monitoring of biologic processes such as cell metabolic behavior and proliferation, and has proven useful as a research tool for understanding tumor biology. While it does not have a well-defined role in breast cancer for the purposes of screening, diagnosis, or prognosis, emerging PET technologies and uses could expand the applications of PET in breast cancer. Positron emission mammography may provide an alternative adjunct imaging modality for the screening and diagnosis of high-risk patients unable to tolerate MRI. The development of radiotracers with the ability to measure hormonal activity could provide a non-invasive way to assess hormone receptor status and functionality. Finally, the role of PET technologies in monitoring early treatment response may prove particularly useful to research involving new therapeutic interventions.

Hepatocellular carcinoma and gastroenteropancreatic neuroendocrine tumors: potential role of other positron emission tomography radiotracers

18F-Fluorodeoxyglucose avidity for gastroenteropancreatic neuroendocrine tumors and hepatocellular carcinoma is variable, depending on the underlying tumor biology. Experience with non-fluorodeoxyglucose (FDG) tracers (eg, 18F-labeled amine precursors l-dihydroxyphenylalanine and 68Ga-DOTA-peptides for gastroenteropancreatic neuroendocrine tumors and radiolabeled acetate or choline for hepatocellular carcinoma) is evolving and expanding rapidly. This article reviews the role of FDG and non-FDG radiotracers in the imaging evaluation of patients with gastroenteropancreatic neuroendocrine tumors or hepatocellular carcinoma.

Specificity and sensitivity of ⁹⁹mTc-EDDA/HYNIC-Tyr³-octreotide (⁹⁹mTc-TOC) for imaging neuroendocrine tumors

OBJECTIVES

Gastroenteropancreatic neuroendocrine tumors (NETs) are cancers originating from neuroendocrine organs such as the pancreas, pituitary, thyroid, and adrenal glands and tumors arising from the diffuse neuroendocrine cells that are widely distributed throughout the body. NETs express somatostatin (SS) and contain a high density of SS receptors; therefore, they can be specifically targeted with SS-based radiopharmaceuticals. The aim of this research was to determine the validity in terms of specificity, sensitivity, and the agreement beyond chance with the biopsy (gold standard) of the ⁹⁹mTc-EDDA-HYNIC-Tyr³octreotide (⁹⁹mTc-TOC) to image and localize NETs and their metastases.

MATERIALS AND METHODS

Freeze-dried kits containing 0.0125 mg HYNIC-octreotide and co-ligands were easily labeled and quality controlled within the hospital radiopharmacy. Fifty-six consecutive Mexican patients with a previous presumptive diagnosis of NETs underwent several clinical and laboratory studies and were referred to the Nuclear Medicine Department for a routine scan with ⁹⁹mTc-TOC. The patients were injected with 500-600 MBq ⁹⁹mTc-TOC, and whole-body images were obtained 2 h later with a SPECT or a SPECT/CT camera. Two nuclear medicine physicians observed the images and classified them as 17 negative and 39 positive. After correlating the image of each patient with our 'gold standard' (biopsy, clinical history, morphological images, and tumor marker assays), the ⁹⁹mTc-TOC images were classified by the same two physicians as 12 true negatives, five false negatives, 38 true positives and one false positive.

RESULTS

The validity of ⁹⁹mTc-TOC in terms of relative frequencies with corresponding 95% confidence intervals were as follows: 92.3% (64-100%) specificity; 88.4% (78-97%) sensitivity; and the agreement beyond chance was 73% (60-84%). The positive predictive value was 97.4% (87-100%); the negative predicted value was 70.6% (48-93%); the accuracy was 89.3% (89-97%); and the prevalence was 76.8% (64-87%).

CONCLUSION

Because of these high values, we strongly recommend scintigraphy with the Mexican-produced ⁹⁹mTc-TOC for the localization of NETs and their metastases, and we conclude that it is a good tool for detecting neuroendocrine disease in a Mexican population.