When doctors need to examine the inner workings of the body, they are most likely going to recommend a PET scan. A positron emission tomography (PET) scan shows images of organs and tissues and how they are functioning. It is used in the detection of several diseases including heart disease, cancer and brain disorders. Doctors introduce a tracer into the system and areas with high chemical activity show up on the screen as bright spots. These bright spots are usually the areas affected by disease.
With cancer cells, they appear as bright spots due to its higher metabolic rate compared to normal cells. A PET scan will help detect cancer and show how far it has spread. In some instances, cancers may not show on the scan. Possible reasons include:
- It is common for patients to receive a diagnosis for cancer of unknown primary. This means that the test has found cancer in areas where it spread to but hasn’t detected where it started from or the primary site. Cancers are classified and treated according to the primary site, such that cancer that starts in the breast and spreads to the lungs is known as breast cancer with lung secondaries or metastases.
- There is a possibility the primary cancer may be too small for the test to detect while the secondary cancer grows very fast and large, overshadowing the primary. Small cancers will also not cause any symptoms.
- It is also possible that the immune system successfully fought off the primary cancer while the secondary cancer continues growing. This is rare but it remains a possibility.
It may be worrisome to many but primary cancers sometimes don’t show up on scans. The scan may have missed it but the treatment plan will most likely take it down. As long as doctors are offering targeted treatment, treatment will reach the affected area and work accordingly.