Diagnostic methods
Useful tests for the early detection and staging of tumors include X-ray, endoscopy, isotope scan, computed tomography scan, and magnetic resonance imaging, but the single most important diagnostic tool is a biopsy for direct histologic study of tumor tissue. Biopsy tissue samples can be taken by curettage, fluid aspiration (pleural effusion), fine-needle aspiration biopsy (breast), dermal punch (skin or mouth), endoscopy (rectal polyps), and surgical excision (visceral tumors and nodes).
Tumor markers are assuming a growing role in all aspects of cancer care, starting from screening to follow-up after treatment.
A tumor marker is a substance found in the blood, urine, or body tissues that can be elevated in cancer, among other tissue types. There are many different tumor markers, each indicative of a particular disease process, and they are used in oncology to help detect the presence of cancer. An elevated level of a tumor marker can indicate cancer; however, there can also be other causes of the elevation.
Tumor markers can be produced directly by the tumor or by non-tumor cells as a response to the presence of a tumor. Most tumor markers are tumor antigens, but not all tumor antigens can be used as tumor markers.
Examples of tumor markers include alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA), human chorionic gonadotropin (HCG), lactate dehydrogenase (TDH), prostate-specific antigen (PSA) and neuron-specific enolase (NSE) (Image 9.1).
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| Image 9.1 Tumor markers |
Uses of tumor markers can broadly be classified as follows:
§ Screening for common cancers on a population basis. Example: elevated PSA suggests prostate cancer.
§ Monitoring of cancer survivors after treatment.
Example: elevated AFP in a child previously treated for teratoma suggests relapse with endodermal sinus tumor.
§ Diagnosis of specific tumor types, particularly in certain brain tumors and other instances where biopsy is not feasible.
Note! Each diagnostic method has false positive and false negative results. At a false positive finding of the tumor marker is positive, although there is no tumor. With a false negative result of the finding is negative, although there is a tumor. Both possibilities are found among the vast majority of fatally tumor markers so frequently that the oncology professional societies, the determination of tumor markers for targeted tumor diagnosis (except for very few exceptions) strictly reject! There are some diseases that can lead to an increase in tumor markers, although there is no tumor. In smokers, some of these markers are always elevated, although there is no cancer.
The ideal tumor marker would be produced exclusively by a malignant tissue, or would be elevated in tissue predisposed to progressing towards a malignancy. Such a tumor marker would be elevated in the blood of all patients with this particular cancer. This tumor marker would be highly sensitive to detect early stage disease. It would also be sufficiently specific to safe guard against false-positive results. Unfortunately so far this ideal tumor marker does not exist.
Why did the societies reject the tumor marker screening? Because the probability is too small to detect a tumor in a more well-treatable stage. The benefits are much smaller than the harm that is caused by this.
Tumor markers have an advantage?
Only when a particular tumor has occurred, it makes sense to determine the matching or the tumor markers.