Impact Of Imaging Diagnostics On Cancer In Relation With Tumor Markers

Tumor biomarkers have improved with time for prognosis and monitoring purposes mainly, but for earlier detection and risk assessment their development have not yet reached a level adequate for clinical applications. In the past two decades, noninvasive imaging technology based on various platforms for cancer diagnostics has made significant advances with the surrounding computer-aided technologies, not only for clinical applications but also for basic research (13).

In the case of lung cancer, early detection is needed to improve prognosis because most cancers are metastasized when first detected by biomarkers or by cytological assessment of sputum. Mass screening for lung cancer with low-dose X-ray spiral computerized tomography (CT) in mobile units was performed on 5483 individuals from the general population in Japan (13). The detection rate with CT was 0.48%, including cancers of less then 10 mm in diameter, whereas that of standard mass screenings done previously in the same area were 0.03-0.05%, 10 times less sensitive. This high-resolution CT also constitutes an excellent tool for confirmatory discrimination of subtypes of small peripheral lung peripheral adeno-carcinomas (71). Magnetic resonance imaging (MRI) on preoperative local staging of patients with pancreatic cancer was applied to discriminate resectability. MRI results showed 98% sensitivity, 92% specificity, and 96% accuracy in patients with suspected pancreatic tumor (72). MRI-guided intervention is now expanding to diagnosis and treatment of prostate cancer, as in the case of fiber-guided endoscopy for colorectal or gastric cancer.

A recently developed method, optical coherence tomography (OCT) combined with optical fiber may differentiate flat malignant from inflammatory lesions, without requiring biopsy. Ultrasonography with improved resolution is now a common screening tool for the physical check-up of healthy individuals.

Ultrasonography used as a second-line test to serum CA125 shows an increased detection sensitivity in ovarian cancer (73), similar to the combination of occult blood testing with fiber endoscope in colorectal cancer.

Positron emission tomography (PET), which produces images by detecting the radiation given off by tracer molecules, has improved in terms of sensitivity; its applications have also been expanded through the development of new tracers responding to specific targets. PET using tracers responding to target genes are being adapted to gene expression study in experimental animals (14). PET imaging of HSV1-tk expression using thymidine analog called FIAU labeled with radioisotope was used in a clinical gene-therapy trial.

Imaging technologies in diagnostics of cancer have acquired a strong position in relation to molecular and biomarkers in serum or tissue. Advancements in imaging technology will soon lead to the development of a downsized and more cost-effective system with higher resolution that will be easier to use. Without additional improvement, most tumor markers could serve as supplemental tools to imaging diagnosis in the near future. The development of tumor markers as possible tracers with the intervention of imaging analysis, a form of functional molecular imaging analysis, and the development of new primary test markers prior to the application of imaging diagnostics, are promising paths to explore for cancer testing. However, imaging technologies are limited in the sense that they cannot predict cancer risk or provide information on the aggravation of the disease (74).

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