A black spot, or pulmonary nodule, on a lung X-ray is sometimes an early warning sign of lung cancer, but this is not always the case, reports Healthline. Other causes include benign nodules caused by fungal or bacterial infections, including pneumonia and meningitis. Tuberculosis also causes black spots.
Scarring from previous lung infections is also a source of spots on the lungs, according to Healthline. Benign tumors, or hamartoma, are an additional cause.
Doctors generally order a chest X-ray as an initial test to determine if there are masses or spots on the lungs, notes Healthline. Although it is not always possible to detect lung cancer via a chest X-ray, normal X-ray studies can usually determine whether or not lung cancer is a likely cause of symptoms.