Most malignant tumours are not visible and are detected by an examination or preventive check-up by X-rays, CT, sonography, nuclear spin or PET (positron emission tomography). If the tumour is malignant or not, cannot be seen, beside of an indication in PET. The next step is to control growth and/or get a tissue sample that is examined by a pathologist being specialized in cancer. Most people (and many physicians) think he will be able to decide with a nearly absolute certainty, whether it is cancer or not.
The facts are different however. In all good labs from time to time a second examination of the same sample is performed, to know how certain are my results. In the reference centre for bone tumours in Basel 8464 samples had been examined a second time by another pathologist. These second examiners came to a different result in 3440 cases (40%) (Universitätsspital Basel). All examinations had been performed by specialized experts. In other second examinations in England the results even had been worse. As a result of these examinations breast and legs are amputated and therapies with highly poisonous substances are started.
Our advices to all afflicted persons: ask for a second diagnosis independent from the first. It is your life.
Another important diagnostic instrument is tumour markers.
Except of thyroglobulin and prostate specific antigen (PSA) these markers are not really specific for an organ and can be caused by other reasons as well. Specificity of PSA is only 53% (Partin, Oesterling 1994; Zellweger, Gasser 2003). By flipping a coin you will get a specificity of 50%. No tumour marker really mirrors the development of a tumour, neither positively nor negatively. Please be not confused by these laboratory parameters.