Shoulder pain could be a sign of lung cancer.
Lung cancer can cause shoulder pain in different ways. The cancerous growth that appears in the upper half of the lung is called a Pancoast tumor, and it can put pressure on some of the nerves that reach the shoulders, arms, spine and head.
This can cause a group of symptoms referred to as "Horner syndrome," and the symptoms of that syndrome include the following:
Sharp soreness in the shoulder, weakness in one of the eyelids, reduced size of the pupil in one eye and decreased sweating on the affected side of the face.