Medical examinations can be divided into:
- imaging tests, i.e. x-ray, CT, PET, scintigraphy, magnetic resonance, echography etc.
- blood tests, including tumor markers.
With regard to imaging tests, a small nodule of a few millimeters in the lung of a person who has had bronchitis in the past is no cause for alarm, while a lung nodule of 3 cm that was not seen in previous imaging tests will sound an alarm bell. In this latter case, the “signal” is given both by the size of the nodule and by its evolution.
A danger signal may also come from blood tests. However, it is very unlikely that blood tests alone, in the absence of symptoms or major radiological findings, will provide a strong signal.
With regard to blood tests, tumor markers constitute a particular case. Tumor markers are proteins produced by tumors, and can be measured in the blood. Their importance is obvious. A sample of blood is taken; if the marker is detected in the sample, presumably there is a tumor; if the marker is absent, presumably there is no tumor.
Unfortunately, however, it’s not as simple as that; if it were, the entire healthy population could be screened for these markers, tumors could be diagnosed as early as possible and an extremely high percentage of patients would be cured by surgery alone. But that’s not the way it is.
In fact, testing for tumor markers is not recommended by the international cancer prevention guidelines (THE “ABC” OF PREVENTION). Indeed, many tumors do not produce markers, the levels of which will therefore remain normal even if there is a tumor. On the other hand, many noncancerous conditions can raise the level of these markers even if there is no tumor. This means that tumor markers are only used as an aid to diagnosis, and that the diagnosis must be based on several elements, not only on an increased level of markers.