29. F-18 FDG PET for Suspected or Confirmed Regional Recurrence of Colon Cancer. A Prospective Study of Impact and Outcome

Imaging of Tumor Metabolism Using Positron Emission Tomography (PET)

Molecular imaging employing PET/CT enables in vivo visualization, characterization, and measurement of biologic processes in tumors at a molecular and cellular level. Using specific metabolic tracers, information about the integrated function of multiple transporters and enzymes involved in tumor metabolic pathways can be depicted, and the tracers can be directly applied as biomarkers of tumor biology. In this review, we discuss the role of F-18-fluorodeoxyglucose (FDG) as an in vivo glycolytic marker which reflects alterations of glucose metabolism in cancer cells. This functional molecular imaging technique offers a complementary approach to anatomic imaging such as computed tomography (CT) and magnetic resonance imaging (MRI) and has found widespread application as a diagnostic modality in oncology to monitor tumor biology, optimize the therapeutic management, and guide patient care. Moreover, emerging methods for PET imaging of further biologic processes relevant to cancer are reviewed, with a focus on tumor hypoxia and aberrant tumor perfusion. Hypoxic tumors are associated with poor disease control and increased resistance to cytotoxic and radiation treatment. In vivo imaging of hypoxia, perfusion, and mismatch of metabolism and perfusion has the potential to identify specific features of tumor microenvironment associated with poor treatment outcome and, thus, contribute to personalized treatment approaches.

Doing more harm than good? Do systematic reviews of PET by health technology assessment agencies provide an appraisal of the evidence that is closer to the truth than the primary data supporting its use?

Health technology assessment (HTA) has the objective of providing individual patients, clinicians, and funding bodies with the highest-quality information on the net patient benefits and cost effectiveness of medical interventions. Founded on systematic reviews of the available evidence, HTA aims to reduce bias and thereby provide a more valid evaluation of the benefits of new medical interventions than the primary studies themselves. Competing with the traditional role of medical experts, HTA agencies have gained considerable influence over public opinion and policy. The fundamental tenets of evidence-based medicine mandate that this influence should be used first and foremost for the benefit of patients. Over nearly 2 decades, multiple HTA systematic reviews in many countries have discredited most or all of the evidence pertaining to the ability of PET to improve patient-important outcomes. These determinations have delayed, restricted, and, in many cases, prevented access to this technology, especially by cancer patients. HTA systematic review findings are very much at variance with the opinion of clinicians. Our scrutiny of these reviews, benchmarking them against the core values of science and evidence-based medicine, has revealed errors of fact, inappropriate exclusion of pertinent data, and injudicious appraisal of the clinical relevance of evidence, potentially introducing bias into these reviews and compromising the validity of their conclusions about the net patient benefits of PET. We believe that our findings mandate that the molecular imaging community actively engage institutionalized HTA agencies to ensure appropriate representation of our primary data and adherence to the highest principles of evidence-based medicine.

FDG PET and PET/CT for colorectal cancer

The evaluation of patients with known or suspected recurrent colorectal carcinoma is now an accepted indication for positron emission tomography using (18)F-fluorodeoxyglucose (FDG-PET) imaging. PET and CT are complimentary, and therefore, integrated PET/CT imaging should be performed where available. FDG-PET/CT is indicated as the initial test for diagnosis and staging of recurrence, and for preoperative staging (N and M) of known recurrence that is considered to be resectable. FDG-PET imaging is valuable for the differentiation of posttreatment changes from recurrent tumor, differentiation of benign from malignant lesions (indeterminate lymph nodes, hepatic, and pulmonary lesions), and the evaluation of patients with rising tumor markers in the absence of a known source. The addition of FDG-PET/CT to the evaluation of these patients reduces overall treatment costs by accurately identifying patients who will and will not benefit from surgical procedures. This new powerful technology provides more accurate interpretation of both CT and FDG-PET images and therefore more optimal patient care. PET/CT fusion images affect the clinical management by guiding further procedures (biopsy, surgery, and radiation therapy), excluding the need for additional procedures, and changing both inter- and intramodality therapy.

FDG-PET in colorectal cancer

[18F]Fluorodeoxyglucose (FDG) positron emission tomography (PET) is a useful imaging tool in the evolving management of patients with colorectal carcinoma. This technique is able to measure and visualize metabolic changes in cancer cells. This feature results in the ability to distinguish viable tumor from scar tissue, in the detection of tumor foci at an earlier stage than possible by conventional anatomic imaging and in the measurement of alterations in tumor metabolism, indicative of tumor response to therapy. Nowadays, FDG-PET plays a pivotal role in staging patients before surgical resection of recurrence and metastases, in the localization of recurrence in patients with an unexplained rise in serum carcinoembryonic antigen and in assessment of residual masses after treatment. In the presurgical evaluation, FDG-PET may be best used in conjunction with anatomic imaging in order to combine the benefits of both anatomical (CT) and functional (PET) information, which leads to significant improvements in preoperative liver staging and preoperative judgment on the feasibility of resection. Integration of FDG-PET into the management algorithm of these categories of patients alters and improves therapeutic management, reduces morbidity due to futile surgery, leads to substantial cost savings and probably also to a better patient outcome. FDG-PET also appears to have great potential in monitoring the success of local ablative therapies soon after intervention and in the prediction and evaluation of response to radiotherapy, systemic therapy, and combinations thereof. This review aims to outline the current and future role of FDG-PET in the field of colorectal cancer.

18-Fluorodeoxyglucose positron emission tomography has limited sensitivity for colonic adenoma and early stage colon cancer

BACKGROUND

18-Fluorodeoxyglucose positron emission tomography (PET) is used clinically to detect recurrent colon cancer after surgical resection, but the sensitivity of PET for premalignant colon lesions and early stage colon cancer is not well defined.

METHODS

In a prospective study, 45 patients with a total of 58 colonic neoplasms, including premalignant polyps, premalignant, flat lesions, and early stage cancers, were evaluated by PET.

RESULTS

The sensitivity of PET for cancer was 62% (8/13). PET detected 100% (7/7) of cancers 2 cm or larger but only 17% (1/6) of cancers smaller than 2 cm. PET detected 23% (3/13) of flat, premalignant lesions; 70% (7/10) of protruded, premalignant lesions 3 cm or larger; 38% (3/8) of protruded, premalignant lesions between 2 and 2.9 cm; and 14% (2/14) of protruded, premalignant lesions between 1 and 1.9 cm. There was no false-positive PET reading.

CONCLUSIONS

PET has limited sensitivity for flat, premalignant lesions; protruded, premalignant lesions smaller than 3 cm; and colon cancers smaller than 2 cm.

PET and PET-CT for evaluation of colorectal carcinoma

The evaluation of patients with known or suspected recurrent colorectal carcinoma is now an accepted indication for positron emission tomography using (18)F-fluorodeoxyglucose (FDG-PET) imaging. FDG-PET does not replace imaging modalities such as computed tomography (CT) for preoperative anatomic evaluation but is indicated as the initial test for diagnosis and staging of recurrence and for preoperative staging (N and M) of known recurrence that is considered to be resectable. FDG-PET imaging is valuable for the differentiation of posttreatment changes from recurrent tumor, differentiation of benign from malignant lesions (indeterminate lymph nodes, hepatic and pulmonary lesions), and the evaluation of patients with rising tumor markers in the absence of a known source. The addition of FDG-PET to the evaluation of these patients reduces overall treatment costs by accurately identifying patients who will and will not benefit from surgical procedures. Although initial staging at the time of diagnosis is often performed during colectomy, FDG-PET imaging is recommended for a subgroup of patients at high risk (with elevated CEA levels) and normal CT and for whom surgery can be avoided if FDG-PET shows metastases. Screening for recurrence in patients at high risk has also been advocated. FDG-PET imaging seems promising for monitoring patient response to therapy but larger studies are necessary. The diagnostic implications of integrated PET-CT imaging include improved detection of lesions on both the CT and FDG-PET images, better differentiation of physiologic from pathologic foci of metabolism, and better localization of the pathologic foci. This new powerful technology provides more accurate interpretation of both CT and FDG-PET images and therefore more optimal patient care. PET-CT fusion images affect the clinical management by guiding further procedures (biopsy, surgery, radiation therapy), excluding the need for additional procedures, and changing both inter- and intramodality therapy.

Positron emission tomography for evaluation of colorectal carcinoma

Evaluation of patients with known or suspected recurrent colorectal carcinoma is now an accepted indication for FDG PET imaging. FDG PET does not replace imaging modalities such as CT for preoperative anatomic evaluation but is indicated as the initial test for diagnosis and staging of recurrence and for preoperative staging (N and M) of known recurrence that is considered to be resectable. FDG PET imaging is valuable for differentiation of posttreatment changes from recurrent tumor, differentiation of benign from malignant lesions (indeterminate lymph nodes, hepatic and pulmonary lesions), and evaluation of patients with rising tumor markers in the absence of a known source. Addition of FDG PET to the evaluation of these patients reduces overall treatment costs by accurately identifying patients who will and will not benefit from surgical procedures. Although initial staging at the time of diagnosis is often performed during colectomy, FDG PET imaging is recommended for a subgroup of patients at high risk (with elevated CEA levels) and normal CT and for whom surgery can be avoided if FDG PET shows metastases. Screening for recurrence in patients at high risk has also been advocated. FDG PET imaging seems promising for monitoring therapy, but larger studies are necessary.