A 21mm shadow on the lungs is not necessarily cancer, but may also be other benign diseases of the lungs. If cancer is suspected, a puncture biopsy can be performed for pathologic tests.
In addition to the occupation of lung cancer in the lungs, the presence of lung inflammation, tuberculosis, abscess and other benign tumors in the lungs may be manifested as the presence of shadows in the lungs under CT or X-ray.
If the patient finds a 21 mm shadow on the lung, he/she can do further enhanced CT examination and puncture biopsy to confirm the diagnosis if necessary.
The chances of lung cancer in a lung shadow are very low and further investigations are required. The nature of the shadows should be clarified, and if there are surgical indications, the patient needs to undergo aggressive surgical treatment.