The expanding role of PET technology in the management of patients with colorectal cancer

The metabolic parameters based on volume in PET/CT are associated with clinicopathological N stage of colorectal cancer and can predict prognosis

Background

A combination of positron emission tomography and computed tomography (PET/CT) is an important modality for the diagnosis of carcinoma. Metabolic tumor volume (MTV) and total lesion glycolysis (TLG) have been reported as metabolic parameters in PET/CT since the late 1990s, and they are expected to be useful in diagnosing diverse cancers and as prognostic biomarkers. We evaluated the potential of these parameters in the prognosis of colorectal cancer (CRC) by comparing them with conventional parameters, including the maximum standardized uptake value (SUVmax). We enrolled 84 patients who underwent surgery for CRC without distal metastasis between April 2015 and April 2019. SUVmax, MTV, and TLG were measured by ¹⁸F-fluorodeoxyglucose (FDG)-PET/CT. To find an optimal threshold value related to prognosis, the volume of interest in the primary carcinoma was measured at fixed relative and absolute thresholds based on SUVmax (30%, 40%, and 50%; 2.5, 3.0, and 3.5, respectively), tumor-to-liver standardized uptake ratios, TLR (1.0, 1.5, and 2.0), and SUV normalized to lean body mass, SUL (2.0, 2.5, and 3.0). After classifying the patients into two groups according to pathological N stage, the optimal threshold values of all metabolic parameters were compared between groups using a non-parametric comparison test.

Result

The most suitable thresholds for MTV were a SUVmax of 3.5 and a TLR 2.0. TLG with a SUVmax value of 40% showed the most significant difference. The MTV standard uptake ratio of 2.0 was significantly associated with pathological N stage.

Conclusion

Our results suggest that an MTV TLR 2.0 on PET/CT reflects pathological N stage in local patients with CRC.

Practice and prospects for PET/CT guided interventions

During the past 10 years, performing real-time molecular imaging with positron emission tomography (PET) in combination with computed tomography (CT) during interventional procedures has undergone rapid development. Keeping in mind the interest of the nuclear medicine readers, an update is provided of the current workflows using real-time PET/CT in percutaneous biopsies and tumor ablations. The clinical utility of PET/CT guided biopsies in cancer patients with lung, liver, lymphoma, and bone tumors are reviewed. Several technological developments, including the introduction of new PET tracers and robotic arms as well as opportunities provided through acquiring radioactive biopsy specimens are briefly reviewed.

Application and Indication of Carcinoembryonic Antigen Triggered 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography Scanning in the Detection of Relapse of Colorectal Cancer Patients After Curative Therapy

OBJECTIVE

This study aimed to explore the characteristics of patients with colorectal cancer (CRC) following curative therapy that may benefit from fluorine-18-2-uoro-2-deoxy-D-glucose positron emission tomography/computed tomography (F-FDG PET/CT) scanning, evaluate the application of carcinoembryonic antigen (CEA)-triggered F-FDG PET/CT scanning, and provide referential indicators.

METHODS

This retrospective study included 56 CRC patients who received a PET/CT scan as a primary examination because of rising CEA levels after curative therapy and who had not received any other radiological examinations previously.

RESULTS

The rate of recurrence or metastasis was 75.0% by PET/CT scan but was 69.6% with follow-up treatment. The sensitivity, specificity, accuracy, positive predictive value, and negative predictive value were 94.9%, 70.6%, 87.5%, 88.1%, and 85.7%, respectively. TNM (tumor, node, metastasis) stage, body mass index, and CEA level were significant prognostic factors.

CONCLUSIONS

Positron emission tomography/CT can be selectively applied as a primary examination in CRC patients with asymptomatic elevation of CEA. High CEA levels, increased body mass index, and advanced TNM staging are risk factors for relapse.

[Modern imaging of liver metastases]

CLINICAL/METHODICAL ISSUE

The liver is the second most common location of metastases following the lymph nodes. The accurate characterization of focal liver lesions in oncology patients is especially important because of the high prevalence of benign liver lesions and the possibility of co-existing benign and malignant lesions. The exact interpretation of these lesions is crucial for therapeutic decisions and thus for the prognosis of the patient.

STANDARD RADIOLOGICAL METHODS

It is essential to detect all focal liver lesions and to distinguish benign from malignant lesions, especially in the management of oncology patients. Numerous imaging modalities are available for these challenges in the daily routine. An extensive understanding of the advantages and limitations of the various imaging modalities and knowledge of the morphology and the typical and atypical appearances of the different metastases is important.

METHODICAL INNOVATIONS

This review explains the radiological criteria for various metastases in different modalities. To evaluate the individual prognosis and risk assessment preoperatively, functional imaging is necessary. These personalized pretherapeutic diagnostics are discussed.

Performance of intra-procedural 18-fluorodeoxyglucose PET/CT-guided biopsies for lesions suspected of malignancy but poorly visualized with other modalities

PURPOSE

We sought to evaluate the safety and the diagnostic success rate of percutaneous biopsies performed under intra-procedural (18)F-deoxyglucose (FDG) positron-emission tomography/computed tomography (PET/CT) guidance for lesions difficult to see with conventional cross-sectional imaging.

METHODS

From 2011 to 2013, consecutive clinically indicated percutaneous PET/CT-guided biopsies of 106 masses (mean size, 3.3 cm; range, 0.7-15.9 cm; SD, 2.9 cm) in bones (n = 33), liver (n = 26), soft tissues (n = 18), lung (n = 15) and abdomen (n = 14) were reviewed. The biopsy procedures were performed following injection of a mean of 255 MBq (SD, 74) FDG. Mean maximal standardized uptake value (SUV) of lesions was 8.8 (SD, 6.3). A systematic review of the histopathological results and outcomes was performed.

RESULTS

Biopsies were positive for malignancy in 76 cases (71.7%, 76/106) and for benign tissue in 30 cases (28.3%, 30/106). Immediate results were considered adequate for 100 PET/CT biopsies (94.3%, 100/106) requiring no further exploration, and for the six others (5.7%, 6/106) benign diagnoses were confirmed after surgery (n = 4) or follow-up (n = 2). The consequent overall sensitivity and the diagnostic success of biopsy were therefore 100%. No significant differences in terms of detection of malignancy were observed between the different locations. Lesions > 2 cm or with SUV > 4 were not significantly more likely to be malignant. Complications occurred after four biopsies (3.7%, 4/106).

CONCLUSION

Intra-procedural PET/CT guidance appears as a safe and effective method and allows high diagnostic success of percutaneous biopsies for metabolically active lesions.

Predictors of initial 18F-fluorodeoxyglucose-positron emission tomography indication among patients with colorectal cancer

OBJECTIVES

To evaluate the determinants of initial F-fluorodeoxyglucose (F-FDG)-PET indication following primary colorectal cancer diagnosis among patients who underwent surgery between January 2000 and December 2007 and who were observed at a single institution for at least 2 years after diagnosis.

METHODS

Of the 530 patients who underwent colorectal cancer resection, 113 patients received at least one F-FDG-PET following diagnosis. Outcome variables included indication and time of the first F-FDG-PET following diagnosis. Potential predictors included disease-level and patient-level characteristics. Univariate and multivariate regression analyses were performed.

RESULTS

Patients diagnosed later in the study period and patients with higher-stage disease were more likely to receive their first F-FDG-PET for initial staging (P<0.001 and P=0.016, respectively). Patients with lower-stage disease were more likely to receive their initial F-FDG-PET for suspected recurrence on conventional imaging. When performed more than 2 years after diagnosis, F-FDG-PET was more likely to be ordered for suspected recurrence either on the basis of conventional imaging or on the basis of patient symptoms/tumor markers (P=0.003 and 0.031, respectively). F-FDG-PET demonstrated disease progression in at least 50% of patients referred for each indication (P=0.037).

CONCLUSION

Higher utilization of F-FDG-PET may be appropriate among patients referred for a number of indications including: initial staging, particularly among those with higher-stage disease; suspected recurrence on conventional imaging among patients with lower-stage disease; and suspected recurrence more than 2 years after diagnosis. Further research is needed to verify these findings.

More than one pulmonary resections or combined lung-liver resection in 79 patients with metastatic colorectal carcinoma

BACKGROUND

The way to select patients who will benefit from surgical resection of pulmonary metastases of colorectal carcinoma (CRC) remains unclear.

METHODS

We analyze overall survival and potential prognostic factors in 101 pulmonary resections of CRC metastases in 79 patients, focusing on cases with repeated pulmonary resection or with hepatic metastasectomy.

RESULTS

Number of pathological pulmonary metastases was higher than that of preoperatively suspected pulmonary nodules in 18% of the resections. Morbidity rate was 16.5%. There was no mortality. Five-year survival rates from the resection of the CRC and from the first pulmonary metastasectomy were 74.6% and 53.3%, respectively. Prognosis did not decrease in patients with history of hepatic metastasectomy or in those in which repeated pulmonary resection was performed. Age ≥70, preoperative carcinoembrionary antigen (CEA) ≥5 ng/dl and mediastinal lymph node involvement entailed worse prognosis. Pathological lymph node involvement and age were shown as independent prognostic factors in the multivariate analysis.

CONCLUSIONS

Resection of pulmonary metastases of CRC is a safe procedure, with 5-year survival rates over 50%. History of resected hepatic metastases or needs for more than one pulmonary resection do not seem to decrease survival rates. Only lymph node involvement and age seem to be clearly associated to worse prognosis.

FDG-PET/CT-guided biopsy of bone metastases sets a new course in patient management after extensive imaging and multiple futile biopsies

A 73-year-old man with a history of prostate and bladder carcinoma and persistent back pain was diagnosed by MRI with multiple vertebral metastases including a compression fracture of T7. He received radiotherapy for pain relief and for vertebral instability with incipient spinal stenosis, but additional targeted systemic therapy was intended. Therefore, multiple attempts at minimally invasive and open biopsies for histological characterisation of the bone metastases were performed, but failed to provide a conclusive specimen, although CT, MRI and bone scintigraphy were used for biopsy planning. Only histopathological analysis of an (18)F-fluorodeoxyglucose-positron emission tomography (FDG-PET)/CT-guided additional biopsy at a site with high metabolic activity yielded the final diagnosis of bone metastases of a neuroendocrine small cell cancer of unknown origin; hence, the patient had a third malignancy requiring a different therapy regimen and diagnostic work-up.

Strict follow-up programme including CT and ¹⁸F-FDG-PET after curative surgery for colorectal cancer

AIM

The risk of local recurrence following curative surgery for colorectal cancer (CRC) is up to 50%. A rigorous follow-up program may increase survival. Guidelines on suitable methods for scheduled follow up examinations are needed. This study evaluates a strict follow-up program including carcinogenic embryonic antigen (CEA), chest X-ray, abdominal ultrasound (US), computed tomography (CT) and (18)F-FDG positron emission tomography (FDG-PET).

METHOD

A cohort of 132 patients, treated by surgery with curative intent for CRC, was included. Patients were followed prospectively with scheduled controls at 3, 6, 12 and 24 months after curative surgery. CEA, chest X-ray, US, CT and FDG-PET supplemented by clinical examination. The end-point was recurrence. Sensitivity and specificity was estimated 2 years after surgery.

RESULTS

Of the 132 patients included in the study, 25 experienced recurrence, detected at scheduled controls (n = 18) and at intervals between them (n = 7). The results of CT and FDG-PET were correlated with recurrence. CT combined with FDG-PET had the highest specificity and sensitivity.

CONCLUSION

A total of 72% of recurrences were detected at scheduled controls. The findings supported a strict follow-up program following curative surgery for colorectal cancer. FDG-PET combined with CT should be included in control programs.

Comparison of magnetic resonance imaging–fluorodeoxy- glucose positron emission tomography fusion with pathological staging in rectal cancer

Background

This study represents an initial experience with combined magnetic resonance imaging (MRI) and [18F]fluorodeoxyglucose positron emission tomography (FDG PET) (MRI–PET fusion) in the primary staging of rectal carcinoma.

Methods

A retrospective analysis of data recorded on patients with rectal cancer was undertaken. Patients requiring long-course radiotherapy were excluded. Chest radiography, abdominal computed tomography and endorectal ultrasonography were performed. In addition, MRI of the pelvis, whole-body FDG PET and MRI–PET fusion were carried out. All patients subsequently underwent anterior resection.

Results

Twenty-three patients with rectal carcinoma (15 men), of median age 60 (range 46–75) years, were enrolled. In tumour (T) assessment, MRI correctly staged 14 of 22 T2/T3 tumours. In lymph node assessment, MRI–PET fusion had a sensitivity of 44 per cent, with a specificity and positive predictive value of 100 per cent. No additional information was acquired from MRI–PET fusion over MRI plus abdominal computed tomography and chest radiography.

Conclusion

MRI–PET fusion adds little to conventional investigations for staging rectal carcinoma.

Functional imaging of colorectal cancer: positron emission tomography, magnetic resonance imaging, and computed tomography

In the past 10 years, overall survival and disease-free survival of patients with colorectal cancer (CRC) has improved substantially because of a combination of factors: (1) more accurate staging as a result of advances in imaging technology; (2) refinements in surgical technique; (3) 'curative' metastasectomy for patients with limited metastatic disease; (4) improvements in radiation therapy planning and greater precision of radiation therapy delivery; and (5) increasing chemotherapeutic options, including antiangiogenic and vascular targeting drugs. In this era of 'personalized medicine,' the increasingly individualized treatment of patients with CRC has highlighted the need for functional imaging techniques in addition to conventional anatomic-based imaging. This review discusses the contribution of positron emission tomography to the clinical management of CRC. In addition, evolving techniques such as dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), DCE computed tomography (perfusion CT), diffusion-weighted MRI, and blood oxygenation level-dependent MRI that might have a future role will be covered.

Early prediction of response to first-line chemotherapy by sequential [18F]-2-fluoro-2-deoxy-D-glucose positron emission tomography in patients with advanced colorectal cancer

BACKGROUND

To evaluate [(18)F]-2-fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET), for early evaluation of response to palliative chemotherapy and for prediction of long-term outcome, in patients with metastatic colorectal cancer (mCRC).

PATIENTS AND METHODS

In a randomized trial, patients with mCRC received irinotecan-based combination chemotherapy. FDG-PET was carried out before treatment and after two cycles in 51 patients at two centers. Visual changes in tumor FDG uptake and changes measured semi-automatically, as standard uptake values (SUVs), were compared with radiological response after four and eight cycles.

RESULTS

The mean baseline SUV for all tumor lesions per patient was higher in nonresponders than in responders (mean 7.4 versus 5.6, P = 0.02). There was a strong correlation between metabolic response (changes in SUV) and objective response (r = 0.57, P = 0.00001), with a sensitivity of 77% and a specificity of 76%. There was no significant correlation between metabolic response and time to progression (P = 0.5) or overall survival (P = 0.1).

CONCLUSIONS

Although metabolic response assessed by FDG-PET reflects radiological tumor volume changes, the sensitivity and specificity are too low to support the routine use of PET in mCRC. Furthermore, PET failed to reflect long-term outcome and can, thus, not be used as surrogate end point for hard endpoint benefit.

STa peptide analogs for probing guanylyl cyclase C

Guanylyl cyclase C (GC-C), universally overexpressed on primary and metastatic colorectal carcinoma cells, is activated by endogenous ligands, guanylin, and uroguanylin, and by exogenous 18-residue heat-stable enterotoxins (STa) produced by diarrheagenic bacteria. Two 12-residue STa analogs with alternate combinations of two interlocked disulfide bonds, peptides 3 and 6, were synthesized by orthogonal solid phase synthesis routes. Peptides 3 and 6 bound GC-C with a rank order potency of STa > peptide 3 > peptide 6. Peptides 3 and 6 behaved as agonists in stimulating cGMP production. The results reveal that the toxic domain of STa can be reduced to 12 amino acids.

Evaluating mesorectal lymph nodes in rectal cancer before and after neoadjuvant chemoradiation using thin-section T2-weighted magnetic resonance imaging

PURPOSE

To apply thin-section T2-weighted magnetic resoance imaging (MRI) to evaluate the number, size, distribution, and morphology of benign and malignant mesorectal lymph nodes before and after chemoradiation treatment compared with histopathologic findings.

METHODS AND MATERIALS

Twenty-five patients with poor-risk adenocarcinoma of the rectum treated with neoadjuvant chemoradiation were evaluated prospectively. Thin-section T2-weighted MR images obtained before and after chemoradiation treatment were independently reviewed in consensus by 2 expert radiologists to determine the tumor stage, nodal size, nodal distribution, and nodal stage. Total mesorectal excision surgery after chemoradiation allowed MR nodal stage to be compared with histopathology using kappa statistics. Nodal downstaging was compared using the Chi-square test.

RESULTS

Before chemoradiation, 152 mesorectal nodes were visible (mean, 6.2 mm; 100 benign, 52 malignant) and 4 of 52 malignant nodes were in contact with the mesorectal fascia. The nodal staging was 7/25 N0, 10/25 N1, and 7/25 N2. After chemoradiation, only 29 nodes (mean, 4.1 mm; 24 benign, 5 malignant) were visible, and none were in contact with the mesorectal fascia. Nodal downstaging was observed: 20/25 N0 and 5/25 N1 (p < 0.01, Chi-square test). There was good agreement between MRI and pathologic T-staging (kappa = 0.64) and N-staging (kappa = 0.65) after chemoradiation.

CONCLUSIONS

Neoadjuvant chemoradiation treatment resulted in a decrease in size and number of malignant- and benign-appearing mesorectal nodes on MRI. Nodal downstaging and nodal regression from the mesorectal fascia were observed after treatment. MRI is a useful tool for assessing nodal response to neoadjuvant treatment.