Painful bending of the index finger is not related to lung cancer. Only a very small number of patients with non-small cell lung cancer will have lung hypoxia, which leads to enlargement of the finger end but does not cause painful bending of the index finger. Common causes of bending pain of index finger are as follows: 1. Tenosynovitis of index finger: patients may have tenosynovitis on the metacarpal side of index finger, which is manifested as painful nodules on the palmar side of the metacarpophalangeal joint of index finger to touch, and pain, popping and inability to move when flexing and extending. Severe patients may have inability to straighten the index finger when flexing or straightening; 2. Index finger arthritis: Some patients may have index finger arthritis with other joint pain and pain when flexing the index finger.