PET and [18F]-FDG in oncology: a clinical update

A small breast cancer detected by PET

A small breast cancer was detected by positron emission tomography (PET) in an asymptomatic individual. Physical examination, mammography and magnetic resonance imaging all failed to identify the tumor. Treatment was partial resection of the breast. Based on the resected specimen, the tumor was 6 mm in diameter. Although previous studies have shown PET to be highly sensitive for the detection of primary breast cancer, detectability of tumors smaller than 1 cm is uncertain. Our case suggests the potential utility of PET for the early detection of primary breast cancer.

In vivo evaluation of the biodistribution of 11C-labeled PD153035 in rats without and with neuroblastoma implants

The biodistribution of 11C-labeled 4-(3-bromoanilino)-6,7-dimethoxyquinazoline, an inhibitor of the epidermal growth factor (EGF) receptor tyrosine kinase, has been evaluated in vivo in rats using positron emission tomography (PET). Time-activity data obtained after i.v. administration in one rat revealed that the radiotracer rapidly cleared from plasma with subsequent uptake in major organs of the body (brain, heart, liver, gastrointestinal tract and bladder). Uptake in proliferating tissue in rats with human neuroblastoma xenografts indicate that [O-11C-methyl]PD153035 shows promise as a new agent for in vivo imaging of tumors with PET.

Usefulness of positron emission tomography imaging in the management of lung cancer

Positron emission tomography imaging is useful for the characterization of the solitary pulmonary nodule and mediastinal staging. Potential future applications include extrathoracic staging to help to determine the ideal site for possible tissue diagnosis, to guide treatment plans, and to monitor the response to therapy and recurrence. Positron emission tomography may also predict prognosis. This review discusses the uses of positron emission tomography, the current literature, and the clinical guidelines for positron emission tomography imaging.

Uncoupling of fatty acid and glucose metabolism in malignant lymphoma: a PET study

Increased use of glucose through glycolysis is characteristic for neoplastic growth while the significance of serum-free fatty acids for regulation of energy metabolism in cancer is poorly understood. We studied whether serum-free fatty acids (FFA) interfere with glycolytic metabolism of lymphoproliferative neoplasms as assessed with 2-F18-fluoro-2-deoxy-D-glucose ([F18]FDG) and positron emission tomography (PET). Twelve patients with newly diagnosed non-Hodgkin's lymphoma (n = 9) or Hodgkin's disease (n = 3) participated in this study before start of oncologic treatment. Each patient underwent two [F18]FDG PET studies within 1 week after overnight fast: once during high fasting serum FFA concentrations and once after reduction of serum FFA by administration of acipimox. Acipimox is a nicotinic acid derivative that inhibits lipolysis in peripheral tissues and induces a striking reduction in circulating FFA concentration. In all cases, dynamic PET imaging over the tumour area was performed for 60 min after injection of [F18]FDG. Both graphical analysis (rMR(FDG)) and single scan approach (SUV) were used to compare tumour uptake of [F18]FDG under high fasting FFA concentrations and after pharmacologically decreased FFA concentrations. Serum FFA concentrations were reduced significantly from 0.92+/-0.42 mmol I(-1)at baseline to 0.26+/-0.31 mmol I(-1) after acipimox administration (P = 0.0003). Plasma glucose, serum insulin and lactate concentrations were similar during both approaches. The retention of glucose analogue [F18]FDG in tumour was similar between baseline and acipimox studies. Median rMR(FDG) of a total of 12 involved lymph nodes in 12 patients was 21.9 micromol 100 g(-1) min(-1) (range 8.7-82.5) at baseline and 20.1 micromol 100 g(-1) min(-1)(range 10.7-81.7) after acipimox. The respective values for median SUV were 7.8 (range 3.6-18.6) and 6.0 (range 4.1-20.2). As expected, [F18]FDG uptake in myocardium was clearly enhanced by acipimox due to reduction of circulating FFAs. In conclusion, blood fatty acids appear to have minor significance for [F18]FDG uptake in lymphoma. This suggests that glucose utilization is uncoupled of FFA metabolism and indicates that glucose-free fatty acid cycle does not operate in lymphomatous tissue. Glucose appears to be the preferred substrate for energy metabolism in tumours, in spite of the high supply of FFAs in the fasting state. Although acipimox and other anti-lipolytic drugs have potential for treatment of catabolic state induced by cancer, they are not likely to interfere with tumour energy metabolism which is fuelled by glucose.

The effect of preoperative radiation therapy on glucose utilization and cell kinetics in patients with primary rectal carcinoma

BACKGROUND

Proliferating cells in neoplasms usually show rapid cell cycle times and high rates of glycolysis. Tumor glucose utilization (TuGluc), potential cell doubling time (Tpot), and the effect of radiotherapy (RT) were evaluated in patients with primary rectal carcinoma.

METHODS

2-[18F]-fluoro-2-deoxy-glucose (18F-FDG) was administered and dynamic positron emission tomography (PET) performed to determine TuGluc. Cell kinetics were measured with flow cytometry after labeling with iodo-deoxy-uridine. Two groups of patients were investigated prospectively: 1) those patients undergoing surgery only and 2) those patients undergoing surgery after receiving 30 gray of RT. Twenty consecutive patients with a cT3-NX-M0 tumor and age > 50 years were selected and randomized. One patient was excluded because of unexpected liver metastases and another had incomplete data.

RESULTS

At baseline, the TuGluc for Group 1 was 222+/-104 nmol/mL/minute (mean +/- 1 standard deviation), and was 215+/-126 nmol/mL/minute for Group 2 (P > 0.8). After RT TuGluc decreased to 77+/-39 nmol/mL/minute (P = 0.008). Tpot was 3.4+/-1.2 days for Group 1 and 2.6+/-2.0 days for Group 2 at baseline (P > 0.2). Two weeks after RT, Tpot slowed to 5.7+/-3.6 days (P = 0.04). A weak negative correlation (correlation coefficient = -0.36) was found between TuGluc and Tpot. After RT, the proportion of labeled cells had not changed from baseline levels (P > 0.2), suggesting undisturbed proliferation, but the DNA synthesis time had increased. The significant decrease of TuGluc indicated cell loss.

CONCLUSIONS

Tumor FDG uptake and cell kinetics are not correlated strongly in rectal carcinoma. Preoperative RT results in an overall loss of tumor cells (tumor reduction) and an increase in Tpot, although proliferation of the viable cell fraction is maintained.

F-18-FDG uptake in tuberculosis

Two patients are described who showed abnormal fluorine-18 fluorodeoxyglucose (F-18 FDG) uptake that was due to benign disease, specifically tuberculous lymphadenitis and pneumonitis. The first patient had ulceration and oozing of the left nipple that was related to Paget's disease. An F-18 FDG PET, whole-body scan, which was performed for staging, showed no breast uptake. However, there was intense multifocal uptake in mediastinal, supraclavicular, and para-aortic areas that was confirmed radiologically to represent widespread lymphadenopathy. Pathologic examination of a mediastinal lymph node showed active tuberculosis. The second patient showed intense focal F-18 FDG uptake in mediastinal and supraclavicular areas and para-aortic lymphadenopathy due to non-Hodgkin's lymphoma. In addition, there was abnormal F-18 FDG lung uptake that revealed the presence of acid-fast bacilli on bronchial lavage. Intense focal F-18 FDG uptake in widespread lymphadenopathy or in the lung could be caused by infectious diseases such as tuberculosis. This possibility should be considered when whole-body scans of patients with cancer are interpreted, especially in those with a high incidence of infectious disease.

Applications of PET in lung cancer

An estimated 180,000 new cases of lung cancer will be diagnosed in the United States this year, and lung cancer accounts for approximately 25% of all cancer deaths. The overall 5-year survival rate is 14%, and this has not changed over the past several decades. Lung cancer diagnosis and treatment is a major health problem globally. Most lung cancers are detected initially on chest radiographs, but many benign lesions have radiologic characteristics similar to malignant lesions. Thus, additional studies are required for further evaluation. Computed tomography (CT) is most frequently used to provide additional anatomic and morphologic information about the lesion, but it is limited in distinguishing benign from malignant abnormalities in the lung, pleura, and mediastinum. Because of the indeterminate results from anatomic imaging, biopsy procedures including thoracoscopy and thoracotomy may be used even through one-half of the lesions removed are benign and do not need to be removed. FDG-PET imaging provides physiologic and metabolic information that characterizes lesions that are indeterminate by CT and that accurately stages the distribution of lung cancer. Exploiting the fundamental biochemical differences between cancer and normal tissues, FDG imaging takes advantage of the increased accumulation of FDG in transformed cells. FDG-PET is very sensitive (approximately 95%) for the detection of cancer in patients who have indeterminate lesions on CT. The specificity (approximately 85%) of PET imaging is slightly less than the sensitivity because some inflammatory processes such as active granulomatous infections accumulate FDG avidly. The high-negative predictive value of PET suggests that lesions considered negative on the study are benign, biopsy is not needed, and radiographic follow-up is recommended. Several studies have documented the increased accuracy of PET compared with CT in the evaluation of the hilar and mediastinal lymph node status in patients with lung cancer. If the mediastinum is normal on PET imaging and there is no other evidence of metastatic disease, the patient has a thoracotomy. If the mediastinum is abnormal on PET imaging, mediastinoscopy is performed with the PET images providing the lymph node stations to target. Whole-body PET studies detect metastatic disease that is unsuspected by conventional imaging and demonstrate some of the anatomic abnormalities detected by CT to be benign lesions. Management changes have been reported to occur in up to 41% of patients based on the results of the whole-body studies.

The importance of glucose transport activity as the rate-limiting step of 2-deoxyglucose uptake in tumor cells in vitro

Glucose transporter (GLUT) expression and hexokinase activity are thought to be related to high [18F]-fluorodeoxyglucose (FDG) uptake in tumor cells, but their relative importance is still unknown. To determine which is the predominant factor in FDG uptake in tumor cells, cultured tumor cell lines and a normal cell line were studied in vitro with respect to 2-deoxyglucose (DG) uptake, hexokinase activity, and the initial uptake rate of 3-O-methylglucose (3-O-MG) transport, which is generally accepted as indicating the amount of GLUT expressed on the plasma membrane. In 16 types of tumor cells and one fibroblast cell line, DG uptake was assessed for 60 min, the initial uptake rate of 3-O-MG transport was measured for 1 min, and total hexokinase activity, including that in the mitochondrial fraction, was determined. Across all 16 tumor cell lines, there was a significant correlation between DG uptake and 3-O-MG transport (p = 0.0012, F test), but not between DG uptake and hexokinase activity. Hexokinase activity of the tumor cells was comparable to that of the human fibroblast cells in the exponential growth phase. Most tumor cells showed higher DG uptake and 3-O-MG transport than the human fibroblast cells. The results suggest that DG uptake of cultured tumor cells is governed by GLUT expression, which may be a distinct characteristic of the neoplastic process.

Evaluating tumor biology and oncological disease with positron-emission tomography

The usefulness of positron-emission tomography (PET) for noninvasive assessment of several biological parameters of neoplastic tissue has been reviewed. Numerous radiotracers have been developed, whose particular distribution in the presence of cancer in vivo serves to distinguish medically relevant properties of the tumor cells with which they associate. That distribution is most accurately determined through use of a PET scanner, to localize and quantify the tracer molecules, in which have been incorporated positron-emitting isotopes. These tracers include hypoxia markers, receptor ligands, substrates for enzymatic modification by the products of expression of specific genes, and precursors of protein anabolism and carbohydrate catabolism. In addition, application of PET to evaluation of patients with some particular cancers has been examined, while placing special emphasis on the level of scientific rigor of the evidence underlying conclusions about appropriate use of PET in oncology.

FDG accumulation and tumor biology

The tumoral uptake of fluorine-18-deoxyglucose (FDG) is based upon enhanced glycolysis. Following injection, FDG is phosphorylated and trapped intracellularly. An important mechanism to transport FDG into the transformed cell is based upon the action of glucose transporter proteins; furthermore, highly active hexokinase bound to tumor mitochondria helps to trap FDG into the cell. In addition, enhanced FDG uptake may be due to relative hypoxia in tumor masses, which activates the anaerobic glycolytic pathway. In spite of these processes, FDG uptake is relatively aspecific since all living cells need glucose. Clinical use is therefore recommended in carefully selected patients.

Clinical evaluation of whole-body 18F-fluorodeoxyglucose positron emission tomography in the detection of liver metastases

BACKGROUND

Assessment of metastatic involvement of the liver remains a diagnostic challenge. The objective of this study was to evaluate the potential role of FDG PET in the detection of liver metastases.

PATIENTS AND METHODS

Sixty-four patients with malignancy and possible liver involvement were included. Liver metastases were present in 31 cases, demonstrated by histopathological analysis in 15 cases and by follow-up in 16 cases. The negative cases were confirmed by pathology in four cases, peroperative ultrasonography in 12 cases, and follow-up in 17 cases. Whole-body FDG PET was compared to CT (n = 53) and US (n = 43).

RESULTS

PET demonstrated a 97% sensitivity, an 88% specificity and a 92% accuracy, compared to 93%, 75% and 85%, respectively, for CT (P = NS). Concordant results were obtained in 44 of 64 patients (69%: 19 TP. 25 TN). PET provided new and accurate information in 15 of 64 patients (23.4%). PET demonstrated liver metastases in 11 patients in whom conventional methods yielded negative (two cases) or doubtful (nine cases) results. Four patients free of liver involvement were correctly staged with PET, while CT/US were equivocal. PET was erroneous in five of 64 cases (7.8%, four FP, one FN).

CONCLUSIONS

FDG PET allows an accurate screening of liver involvement in patients with malignancy. Combined with CT, it provides additional diagnostic information that could directly affect the management of these patients.

Utility of FDG-PET for investigating unexplained plasma CEA elevation in patients with colorectal cancer

OBJECTIVE

To assess the potential role of positron emission tomography (PET) with 2-[18F]fluoro-2-deoxy-D-glucose (FDG) in patients with unexplained rising carcinoembryonic antigen (CEA) levels after the treatment of colorectal cancer.

BACKGROUND

A rising CEA level after the resection of colorectal cancer is an early indicator of tumor recurrence. However, conventional imaging techniques have limited sensitivity for detecting recurrent disease in such patients. Especially after surgical intervention, FDG-PET is rapidly gaining an important role in establishing the extent of disease in the oncology patient.

METHODS

Twenty-two patients with abnormal CEA levels and normal results of conventional methods of tumor detection were studied with FDG-PET. The PET results were compared with pathologic findings (n = 9) and long-term radiologic and clinical follow-up (n = 13).

RESULTS

FDG-PET was abnormal in 17 of 22 patients. Tissue sampling was available in 7 of these 17 patients; all of these had recurrent disease. Definitive curative surgical intervention was performed in four patients. Subsequent dedicated imaging findings and clinical course confirmed the presence of extensive disease in 8 of the remaining 10 patients; the PET results in the other 2 patients were considered falsely positive. FDG-PET was negative in 5 of 22 patients. No disease was found by tissue sampling (n = 2) and clinical follow-up (n = 3). Overall, the positive-predictive value for PET was 89%, (15 of 17) and the negative-predictive value was 100% (5 of 5).

CONCLUSIONS

When conventional examinations are normal, FDG-PET is a valuable imaging tool in patients who have a rising CEA level after colorectal surgery.

Detection of recurrent and metastatic colorectal cancer: comparison of positron emission tomography and computed tomography

BACKGROUND

This study evaluates the clinical value of positron emission tomography (PET) with 2-[F-18] fluoro-2-deoxy-D-glucose (FDG) as compared to computed tomography (CT) in patients with suspected recurrent or metastatic colorectal cancer (CRC).

METHODS

A retrospective review of the records of 58 patients who had FDG-PET for evaluation of recurrent or advanced primary CRC was performed. FDG-PET results were compared with those of CT and correlated with operative and histopathologic findings, or with clinical course and autopsy reports.

RESULTS

Recurrent or advanced primary CRC was diagnosed in 40 and 11 patients, respectively. The sensitivity and specificity of FDG-PET were 91% and 100% for detecting local pelvic recurrence, and 95% and 100% for hepatic metastases. These values were superior to CT, which had sensitivity and specificity of 52% and 80% for detecting pelvic recurrence, and 74% and 85% for hepatic metastases. FDG-PET correctly identified pelvic recurrence in 19 of 21 patients; CT was negative in 6 of these patients and equivocal in 4. FDG-PET was superior to CT in detecting multiple hepatic lesions and influenced clinical management in 10 of 23 (43%) patients.

CONCLUSION

FDG-PET is more sensitive than CT in the clinical assessment of patients with recurrent or metastatic CRC, and provides an accurate means of selecting appropriate treatment for these patients.

Improvement in staging of esophageal cancer with the addition of positron emission tomography

BACKGROUND

Positron emission tomography with the glucose analogue 2-[18F]fluoro-2-deoxy-D-glucose (FDG) has been used to detect and stage a variety of malignancies. We hypothesized that FDG-positron emission tomography would improve staging of patients with esophageal cancer and thereby facilitate selection of candidates for resection.

METHODS

Fifty-eight patients (42 men and 16 women) with biopsy-proven esophageal cancer were evaluated with both FDG-positron emission tomography and computed tomography.

RESULTS

In all but 2 patients, increased FDG uptake was identified at the site of the primary tumor. Six patients were not operative candidates. Seventeen patients were not candidates for resection because of metastatic disease. Positron emission tomography identified the metastatic disease in all 17 (12 of whom underwent confirmatory biopsy), whereas computed tomography was positive for metastases in only 5. The remaining 35 patients underwent surgical exploration, were judged to have resectable disease and had esophagectomy. Pathologic examination of resected specimens identified lymph node metastases in 21 patients. These nodes were detected by positron emission tomography in 11 patients and by computed tomography in 6.

CONCLUSIONS

Positron emission tomography improved staging and facilitated selection of patients for operation by detecting distant disease not identified by computed tomography alone.