The emerging role of 18F-fluorodeoxyglucose positron emission tomography in the management of primary and recurrent rectal cancer

A systematic review of the predictive value of 18F-fluoro-2-deoxyglucose positron emission tomography on survival in locally advanced rectal cancer after neoadjuvant chemoradiation

AIM

Treatment of locally advanced rectal cancer (LARC) includes preoperative radiation therapy with or without chemotherapy followed by radical surgery, but the clinical outcome is uncertain. A systemic review was carried out to determine the predictive value of (18)F-fluoro-2-deoxyglucose positron emission tomography ((18)FDG-PET) for assessing disease-free (DFS) and overall survival (OS) in LARC.

METHOD

A literature search (PubMed/MEDLINE, EMBASE, Cochrane) up to January 2012 to identify full papers with sequential (18)FDG-PET and survival data, using indexing terms and free text words. The inclusion criteria were: a study of at least 10 patients, having sequential (18)FDG-PET imaging before and after adjuvant chemoradiation and a minimal follow-up of 24 months. Studies were selected by two of the authors. A meta-analysis was performed for DFS and OS using the hazard ratio (HR) as the primary outcome.

RESULTS

Five eligible studies were identified including 330 patients (mean age 63 years, 64% men), in which PET-CT or PET imaging was used. The American Joint Committee on Cancer stage distribution was as follows: Stage I, 2%; Stage II, 44%; Stage III, 52%; Stage IV, 1%. The pooled HRs for complete metabolic response versus partial or no response were 0.39 (95% CI 0.18-0.86; P = 0.02) for OS and 0.70 (95% CI 0.16-3.14; P = 0.64) for DFS. The lack of significance for DFS might be explained by different follow-up characteristics. There was also clinical heterogeneity among the different studies.

CONCLUSION

This systematic review indicates that complete metabolic response on sequential (18)FDG-PET data after preoperative chemoradiation of LARC is predictive of OS, but not of DFS.

Role of the standardized uptake value of 18-fluorodeoxyglucose positron emission tomography-computed tomography in detecting the primary tumor and lymph node metastasis in colorectal cancers

PURPOSE

To assess the role of positron emission tomography-computed tomography (PET-CT) and multidetector-row CT (MD-CT) in detecting the primary lesion and lymph node metastasis in patients with colorectal cancers.

METHODS

A collective total of 80 lesions resected from 77 patients were examined pathologically. We analyzed the significance of the standardized uptake value (SUV) and its relationship with the clinicopathologic findings of primary lesions and lymph node metastasis. The detectability of primary lesions and lymph node metastases on PET-CT images was compared with that on MD-CT images.

RESULTS

The detectability of primary lesions was better on PET-CT images than on MD-CT images (p = 0.0023). We observed no significant differences in the SUV with respect to staging, tumor grade, lymphatic or vessel invasion, and macroscopic type; however, primary tumor size analysis revealed that tumors larger than 3 cm had a higher SUV than those smaller than 3 cm. The sensitivity of PET-CT for detecting lymph node metastasis was lower than that of MD-CT, but the specificity of PET-CT was higher than that of MD-CT.

CONCLUSIONS

The SUV of primary cancers tends to increase in proportion to tumor size. Although the value of PET-CT in detecting lymph node metastasis is limited, PET -positive lymph nodes can be considered metastatic.

Complete clinical response after neoadjuvant chemoradiation for distal rectal cancer

Multimodality treatment of rectal cancer, with the combination of radiation therapy, chemotherapy, and surgery has become the preferred approach to locally advanced rectal cancer. The use of neoadjuvant chemoradiation therapy (CRT) has resulted in reduced toxicity rates, significant tumor downsizing and downstaging, better chance of sphincter preservation, and improved functional results. A proportion of patients treated with neoadjuvant CRT may ultimately develop complete clinical response. Management of these patients with complete clinical response remains controversial and approaches including radical resection, transanal local excision, and observation alone without immediate surgery have been proposed. The use of strict selection criteria of patients after neoadjuvant CRT has resulted in excellent long-term results with no oncological compromise after observation alone in patients with complete clinical response. Recurrences are detectable by clinical assessment and frequently amenable to salvage procedures.

18F-FDG PET/CT imaging in oncology

Accurate diagnosis and staging are essential for the optimal management of cancer patients. Positron emission tomography with 2-deoxy-2-[fluorine-18]fluoro-D-glucose integrated with computed tomography (18F-FDG PET/CT) has emerged as a powerful imaging tool for the detection of various cancers. The combined acquisition of PET and CT has synergistic advantages over PET or CT alone and minimizes their individual limitations. It is a valuable tool for staging and restaging of some tumors and has an important role in the detection of recurrence in asymptomatic patients with rising tumor marker levels and patients with negative or equivocal findings on conventional imaging techniques. It also allows for monitoring response to therapy and permitting timely modification of therapeutic regimens. In about 27% of the patients, the course of management is changed. This review provides guidance for oncologists/radiotherapists and clinical and surgical specialists on the use of 18F-FDG PET/CT in oncology.

Management of recurrent rectal cancer

BACKGROUND

Here we present a concise review on the evaluation and management of locally recurrent rectal cancer, which despite marked reductions in the rate of recurrent rectal cancer remains an important problem.

METHODS

This educational review discusses the diagnosis, evaluation, and management of recurrent rectal cancer.

RESULTS

Despite improvements in both the neoadjuvant and surgical management of rectal cancer, local recurrence is still an important problem, with documented recurrence rates of 4% to 8%. The local management of recurrence requires a team of specialist. Accurate detection and diagnosis followed by chemoradiotherapy and surgical resection may result in 5-year survival rates of up to 35%.

CONCLUSIONS

We discuss the diagnosis, evaluation, and management of locally recurrent rectal cancer. Locally recurrent rectal cancer can be successfully managed with multimodal therapy leading to successful palliation and often cure.

Recent advances in the management of carcinoma of the rectum

In the last two decades rectal cancer has changed from a surgically managed disease into a multidisciplinary treatment model resulting in considerable improvements in the survival and outcome. This has been made possible by better understanding of the tumor biology and oncogenesis, advances in diagnostic and staging investigations, and the changing concepts in surgical excision; from the days of abdominoperineal resection to the concept of "zone of upward spread" and low anterior resection to the era of total mesorectal excision and transanal excision. Efforts are on the way to risk stratification and identification of predictors of nonoperative management. Impressive advances in the adjuvant therapies have seen a sea change in the form of postoperative radiotherapy to preoperative radiotherapy to preoperative chemoradiotherapy and postoperative adjuvant chemotherapy. This multidisciplinary approach is the key to impressive local control rates, decreased metastatic rates, overall survival, and enhancement in quality of life. Newer ideas in the understanding of genetic differences in rectal cancers have stemmed from the observation that these cancers differ in their response to the adjuvant treatment. The present day research has focused these areas of biologic differences in cancers and aims to target the specific loci in malignant cells with monoclonal antibodies directed against various growth factors, key enzyme inhibition, and genetic manipulation. The future research lies in the study of gene expression, micro-array techniques, molecular markers, and better understanding of the predictors of tumor response to therapy.

Radiation changes do not interfere with postchemoradiation restaging of patients with rectal cancer by FDG PET/CT before curative surgical therapy

PURPOSE

Changes in F-18 fluorodeoxyglucose (FDG) uptake in normal tissues after chemoradiation therapy (CRT) potentially limit the ability of positron emission tomography (PET) to provide early assessment of therapeutic response. This study evaluated whether such changes negatively impact interpretation of posttherapy PET performed within 6 weeks of CRT completion and before definitive surgery in patients with locally advanced rectal cancer. The positive predictive value (PPV) and specificity of post-CRT PET, read clinically, was determined in 63 consecutive rectal cancer patients who had undergone preoperative CRT.

METHODS AND MATERIALS

A schema for identifying and scoring postradiation effects on PET was prospectively defined and applied in a blinded manner. This was compared with initial clinical reporting of response. Histologic assessment of the operative specimens was used as the reference standard. Correlation between clinical proctitis during CRT and radiation changes on subsequent PET was also assessed.

RESULTS

Clinical reporting of post-CRT PET yielded a high PPV (94%; 95% confidence interval, 89--100%) but may have been exaggerated by the low prevalence of complete tumor clearance (16%). The specificity was 80% with only two false-positive results. On blinded reading, significant post-CRT effects on PET were recorded in 4 of 63 patients (6% 95% confidence interval, 0-13%), but pattern recognition converted both false-positive PET results to a complete metabolic response. Clinical CRT proctitis was not correlated with PET findings.

CONCLUSION

Postradiation effects do not appear to significantly compromise the interpretation of PET for therapeutic response assessment. The proposed PET pattern of response may further improve the specificity of PET.

The impact of 18-fluorodeoxyglucose positron emission tomography-computed tomography on the staging and management of primary rectal cancer

PURPOSE

18-Fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET-CT) has a role in recurrent colorectal cancer. This study was designed to assess the impact of PET-CT on management of primary rectal cancer.

METHODS

Eighty-three patients with rectal cancer underwent PET-CT scan between 2002 and 2005. Referring physicians prospectively recorded stage and management plan after conventional imaging before PET-CT scan, which were compared to subsequent stage and management after PET-CT.

RESULTS

Staging PET-CT caused a change in stage from conventional imaging in 26 patients (31 percent). Twelve (14 percent) were upstaged (7 change in N stage; 4 change in M stage; 1 change in N and M stage), and 14 (17 percent) were downstaged (10 change in N stage; 3 change in M stage; 1 change in N and M stage). PET-CT scan altered management intent in seven patients (8 percent) (curative to palliative 6 patients; palliative to curative 1 patient). Management was altered in ten patients (12 percent). There was no difference in impact with respect to tumor height.

CONCLUSIONS

PET-CT scan impacts the management of patients with primary rectal cancer and influences staging/therapy in a third of patients and should be a component of rectal cancer workup.

Patterns of failure and survival for nonoperative treatment of stage c0 distal rectal cancer following neoadjuvant chemoradiation therapy

Neoadjuvant chemoradiation therapy (CRT) is the preferred treatment option for distal rectal cancer. Complete pathological response after CRT has led to the proposal of nonoperative approach as an alternative treatment for highly selected patients with complete clinical response. However, patterns of failure following this strategy remains undetermined. Three hundred sixty-one patients with distal rectal cancer were managed by neoadjuvant CRT including 5-FU, leucovorin, and 5040 cGy. Tumor response assessment was performed at 8 weeks following CRT. Patients with complete clinical response were not immediately operated on and were closely followed. One hundred twenty-two patients were considered to have complete clinical response after the first tumor response assessment. Of these, only 99 patients sustained complete clinical response for at least 12 months and were considered stage c0 (27.4%) and managed nonoperatively. Mean follow-up was 59.9 months. There were 13 (13.1%) recurrences: 5 (5%) endorectal, 7 (7.1%) systemic, and 1 (1%) combined recurrence. All 5 isolated endorectal recurrences were salvaged. Mean recurrence interval was 52 months for local failure and 29.5 months for systemic failure. There were five cancer-related deaths after systemic recurrences. Overall and disease-free 5-year survivals were 93% and 85%. Even though surgery remains the standard treatment for rectal cancer, nonoperative treatment after complete clinical response following neoadjuvant CRT may be safe and associated with good survival rates in a highly selected group of patients. Survival in these patients is significantly affected by systemic failure. Exclusive local failure occurs late after CRT completion and is frequently amenable to salvage therapy.

Patterns of failure and survival for nonoperative treatment of stage c0 distal rectal cancer following neoadjuvant chemoradiation therapy

Neoadjuvant chemoradiation therapy (CRT) is the preferred treatment option for distal rectal cancer. Complete pathological response after CRT has led to the proposal of nonoperative approach as an alternative treatment for highly selected patients with complete clinical response. However, patterns of failure following this strategy remains undetermined. Three hundred sixty-one patients with distal rectal cancer were managed by neoadjuvant CRT including 5-FU, leucovorin, and 5040 cGy. Tumor response assessment was performed at 8 weeks following CRT. Patients with complete clinical response were not immediately operated on and were closely followed. One hundred twenty-two patients were considered to have complete clinical response after the first tumor response assessment. Of these, only 99 patients sustained complete clinical response for at least 12 months and were considered stage c0 (27.4%) and managed nonoperatively. Mean follow-up was 59.9 months. There were 13 (13.1%) recurrences: 5 (5%) endorectal, 7 (7.1%) systemic, and 1 (1%) combined recurrence. All 5 isolated endorectal recurrences were salvaged. Mean recurrence interval was 52 months for local failure and 29.5 months for systemic failure. There were five cancer-related deaths after systemic recurrences. Overall and disease-free 5-year survivals were 93% and 85%. Even though surgery remains the standard treatment for rectal cancer, nonoperative treatment after complete clinical response following neoadjuvant CRT may be safe and associated with good survival rates in a highly selected group of patients. Survival in these patients is significantly affected by systemic failure. Exclusive local failure occurs late after CRT completion and is frequently amenable to salvage 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.

An update on imaging of colorectal cancer

Screening of asymptomatic average-risk patients for presence of colon cancer and early detection in precursor stages is of great interest to general population. Comprehensive evaluation of symptomatic or high-risk patients represents another important clinical focus. Available techniques for total colon imaging, rectal cancer staging and the role of positron emission tomography are discussed.