Pancoast tumor

A pancoast tumor is a type of lung cancer characterized by its position at the top of either lung. It's growth usually compresses one or more of the blood vessels or nerves in the area. It usually appears in smokers.
Horner's syndrome is one of the most common presentations - a constellation of symptoms each caused by the growing tumor - constriction of the pupils, failure to sweat, drooping of one or both eyelids, and one or more sunken eyeballs.
Surgery is contraindicated as it can damage the structures in the area. In most cases, radiation therapy is combined with chemotherapy.
Pancoast tumor at Wikipedia