Metastasis means that cancer has spread to a site that is separate from the original cancer. Finding metastasis carries a worse prognosis. Metastasis can go to various sites in the body and are sometimes discovered on X-ray. X-rays a re however limited in identifying metastasis.
Can X-rays diagnose metastasis?
Metastasis can occur in various sites like the lymph nodes, bones, lungs, various organs, brain, in addition to many others. The diagnosis of metastasis often requires a biopsy. The appearance on X-ray is not diagnostic in many cases. Biopsy is especially important when it will change the management, prognosis and treatment.
Where can X-rays show metastasis?
X-rays will can show metastasis in places like the bones and lungs. X-rays are poor for showing metastasis in organs. X-rays can not tell normal from abnormal soft tissue. X-rays can not show an abnormality within an organ. Both will be white and can not be seen. We can not detect metastasis to the brain on X-rays because we do not see the brain on X-rays. Same goes for organs like the liver, kidneys, etc.
Metastasis to bones
X-rays can sometimes identify metastasis to the bones. Metastasis to the bone will usually be a lytic or sclerotic lesion. Lytic lesion means that there is missing bone or a hole in normal bone. A sclerotic bone lesion is whiter then normal bone. Abnormalities other then metastasis can have this appearance, including benign bone lesions. Many metastasis will not show on X-ray at all, or only if they are big or have significantly replaced the bone.
In the setting of a cancer diagnosis, a bone lesion becomes concerning. This is particularly true if there are multiple bone lesions. A biopsy may be needed to confirm that there is a metastasis to the bone. This is done when the management and treatment changes. A nuclear medicine bone scan or PET scan can be done to evaluate the entire skeleton for additional metastasis.
Metastasis to lungs
Metastasis to the lungs can sometimes be detected on X-ray. Metastasis will usually appear as nodules or round white spots amidst the dark lungs. Metastasis to the lungs can occur from many types of cancers like gastrointestinal, kidney, sarcomas, melanomas in addition to many others.
Nodules in the lungs can represent other diagnosis like infections, septic emboli, inflammatory diseases and scarring from prior infections. In the setting of a cancer diagnosis, lung nodules become concerning. A biopsy can be done to confirm the diagnosis. A PET CT scan can be done for more complete staging.
X-rays can not show metastasis in many places in the body
X-rays can not show metastasis to lymph nodes, organs, and other soft tissues. The density or appearance of metastasis has to be significantly different then the tissue it’s in to show on X-ray. That’s why nodules in the lungs show. You have soft tissue metastasis located in dark air filled lung. Soft tissue metastasis in a soft tissue organ will not show.
X-rays are usually not done as a primary staging test because they are limited in showing metastasis, particularly in the soft tissues like organs. Even in bone and lung, we will only see metastasis some of the time.
CT, MRI and PET scans are used for staging and monitoring cancer for this reason. X-rays are however done very frequently and can sometimes identify abnormalities which become concerning. This will almost always require further testing since abnormalities on X-ray are not diagnostic for cancer.