Screening and early diagnosis

Colorectal Cancer: What has Changed in Diagnosis and Treatment over the Last 50 Years?

Aims and background

This overview focuses on what has changed in the diagnosis and treatment of colorectal cancer over the last 50 years.

Methods

The most important international registers (SEER, European and Italian) as well as the literature have been consulted. Furthermore, many prognostic factors are analyzed with the aim to understand the reasons why 5-year survival has improved over the last two decades.

Results

Since the biologic characteristics of the tumor cannot be changed, improved survival must be supported by concomitant multiple factors, such as earlier diagnosis (as given by a more informed educational behavior and the advent of screening) as well as the wide use of colonoscopy and the technical improvement of surgical and medical treatment. However, it seems that the greatest improvement in survival is limited to 5-year controls, whereas long-term survival does not appear to show any significant improvement.

Conclusions

We can hypothesize that our efforts have just delayed the inevitable end: death. Nevertheless, further research should be done to confirm this hypothesis, perhaps in the field of molecular biology, which may also be the right approach to understanding the biologic aggressiveness of each tumor.

Cancer screening: the importance of outcome measures

Cancer screening is attracting greater attention as a growing number of studies and practice guidelines exhort physicians to screen for an increasing number of malignancies. Central to the evaluation of these studies is both the quality of the evidence and the impact of screening upon clinically relevant outcomes. Although much has been written about the optimal study design for screening studies, surprisingly little has been written about evaluating specific outcome measures employed in such studies. This paper reviews the strengths and limitations of common outcomes employed in cancer screening studies. The relationship between study design and outcome measure is explored. Three key biases (lead-time, length-time, and volunteer) associated with screening studies and methods to minimize them are also reviewed. Potential harms associated with screening are outlined. Although disease-specific mortality may be the most robust and relevant traditional outcome measure, increasing attention is being paid to composite health outcome measures for older populations, including quality of life and cost-based measures.

Mathematical models for the early detection and treatment of colorectal cancer

Colorectal cancer is a major cause of death for men and women in the Western world. When the cancer is detected through an awareness of the symptoms by a patient, typically it is at an advanced stage. It is possible to detect cancer at an early stage through screening and the marked differences in survival for early and late stages provide the incentive for the primary prevention or early detection of colorectal cancer. This paper considers mathematical models for colorectal cancer screening together with models for the treatment of patients. Illustrative results demonstrate that detailed attention to the processes involved in diseases, interventions and treatment enable us to combine data and expert knowledge from various sources. Thus a detailed operational model is a very useful tool in helping to make decisions about screening at national and local levels.

99mTc labeled VIP analog: evaluation for imaging colorectal cancer

Early and reliable diagnosis of colorectal cancer continues to be demanding and challenging. Colorectal cancer cells express Vasoactive Intestinal Peptide (VIP) receptors in high density. We have prepared a VIP analog (TP3654), labeled it with (99m)Tc, and evaluated it in experimental animals as an agent for imaging colorectal cancer. The tissue distribution of (99m)Tc-TP3654 has been compared with that of (111)In-DTPA-Octreotide and (99m)Tc-anti-CEA scan in nude mice bearing human colorectal cancer LS174T. Finally, pharmacokinetic and tissue distribution studies of (99m)Tc-TP3654 have been performed in four normal human volunteers. Data suggest that (99m)Tc-TP3654 can be prepared efficiently without loss of its receptor specificity and biological activity. Although the 24 hr tumor uptake of (99m)Tc-TP3654 in the animal model used was modest (0.21 +/- 0.07% I.D./g), the tissue distribution profile was more favorable than that of (111)In-DTPA-Octreotide or (99m)Tc-anti-CEA scan. Human studies indicated that (99m)Tc-TP3654 had no adverse effect in any subject. Within 24 hours, approximately 70% of the injected dose cleared through the kidneys, and approximately 20% through the hepatobiliary system. In these non-fasting volunteers hepatobiliary clearance was slow and in cancer patients tumor uptake was rapid. Data suggest that (99m)Tc-TP3654 is a promising agent for imaging colorectal cancer.

Use of guanylyl cyclase C for detecting micrometastases in lymph nodes of patients with colon cancer

INTRODUCTION

Guanylyl cyclase C appears to be expressed only in colorectal cancer cells in extraintestinal tissues. Thus, guanylyl cyclase C may be useful as a marker to detect colorectal cancer micrometastases not detectable by histopathology in lymph nodes of patients.

METHODS

Twelve patients with colon adenocarcinoma, Dukes Stages A through C2, and one patient with a tubulovillous adenoma were included in this study. Forty-two lymph nodes were collected from fresh surgical specimens, and each was examined by histopathology and reverse transcription followed by polymerase chain reaction using guanylyl cyclase C-specific primers. Histopathology identified colon cancer cells in 6 of 16 lymph nodes from five Dukes Stage C patients but not in lymph nodes from the patient with a tubulovillous adenoma, the Dukes Stage A patient, or six Dukes Stage B patients. Reverse transcription followed by polymerase chain reaction using guanylyl cyclase C-specific primers was performed on all 42 lymph nodes.

RESULTS

Guanylyl cyclase C messenger RNA was not detected by reverse transcription followed by polymerase chain reaction in lymph nodes from the patient with the tubulovillous adenoma or the patient with Dukes Stage A colon carcinoma. Seven lymph nodes from Dukes Stage C patients revealed guanylyl cyclase C messenger RNA including six lymph nodes containing histopathologically confirmed metastases. Of significance, guanylyl cyclase C messenger RNA was detected in 6 of 21 lymph nodes from Dukes Stage B patients. Indeed, clinical staging of two patients could be upgraded from B to C using reverse transcription followed by polymerase chain reaction and guanylyl cyclase C-specific primers.

CONCLUSION

Reverse transcription followed by polymerase chain reaction using guanylyl cyclase C-specific primers might be useful to more accurately assess micrometastases in lymph nodes of colorectal cancer patients undergoing disease staging.

Colorectal cancer screening

The decision whether to launch a screening program in asymptomatic patients of average risk for colorectal cancer and the selection of the appropriate protocol for screening are complex issues. There are still many unanswered questions. Many organizations such as the American Cancer Society, the World Health Organization Collaborating Center for the Prevention of Colorectal Cancer, and the U.S. National Cancer Institute advocate screening with annual Hemoccult tests and screening with flexible sigmoidoscopy every 3 to 5 years in patients more than 50 years of age. The U.S. Preventive Services Task Force, the Canadian Task Force on Periodic Health Examination, and the International Union Against Cancer have not recommended screening asymptomatic average-risk patients for colorectal cancer. One study showed a small but significant benefit (3 per 1000) of the rehydrated annual Hemoccult test in reducing mortality from colorectal cancer. To embark on a mass screening strategy as recommended, however, would require significant costs, increases in physician training, improved access to the requisite technology, and enhancements in patient and physician compliance. Furthermore, the high false-positive rates of the rehydrated Hemoccult tests would lead to many unnecessary tests, causing greater expense as well as patient discomfort and anxiety. It is, therefore, premature to recommend mass screening for colorectal cancer in asymptomatic individuals at this time. Further research is needed to identify risk factors (such as genetic markers) better and to develop and evaluate screening strategies targeted at those with high risk for colorectal cancer. In the meantime, efforts at primary prevention for the general population should be increased (through nutrition and exercise). Patients over the age of 50 who desire screening should be given information of the benefits and risks of screening and together with their physicians decide on a screening strategy that suits their needs and values.

The potential benefits and harms of screening for colorectal cancer

Australian guidelines for colorectal cancer screening for average-risk populations vary from recommendations for annual screening by faecal occult blood testing for those over 40 years to recommendations that screening may be appropriate if requested by an informed patient aged 50 to 75 years. There are five large screening trials, of which three have published mortality data. A meta-analysis of the mortality data suggests a 19 per cent reduction in colorectal cancer mortality (95 per cent confidence intervals 0.68 to 0.96) with Hemoccult screening. Because of the width of the confidence interval, decisions about the magnitude of the effect of screening should await further trial results, which should be available in the next few years. In the interim, we should examine issues of harm and costs in Australia. For example, in the major trials, over 80 per cent of positive results have been falsely positive and have required invasive investigation. Estimates of the cost-effectiveness of screening for the Australian health system are not yet available and are essential. If the benefits of screening outweight the harms and costs, a successful screening program would require provision of screening infrastructure and appropriate information to target populations, quality control for screening tests and investigations, recall mechanisms to ensure appropriate follow-up of persons with positive results and the active participation of the Australian public and health practitioners.

Nonsteroidal antiinflammatory agents in chemoprevention of colorectal cancer. At what cost?

The objective was to provide a comparison of the known toxicities of nonsteroidal antiinflammatory drugs (NSAIDS) and the likelihood of benefit from colorectal cancer (CRC) chemoprevention attributed to them. Chemoprevention trials require large numbers of subjects followed over many years and are therefore very expensive and difficult. Hence, it is important that agents tested in these trails have a realistic expectation of actual use in the population. Data sources were published literature on the toxicity and CRC chemopreventive activity of NSAIDS. Presently available NSAIDS, used at their usual therapeutic doses, have a serious toxicity rate that quickly exceeds any benefit from CRC prevention. In contrast, low-dose aspirin is worth evaluating, especially because of the potential for simultaneous cardiovascular risk reduction. Possibly, low doses of other NSAIDS may have benefit, but this remains unproven. Synthesis of other NSAIDS, with less toxicity, is another approach towards making the toxicity-benefit ratio more favorable for the use of these agents for CRC prevention.