Damage to the T1-T3 regions of the spinal cord is responsible for drooping of the eyelids (ptosis), constriction of the pupil (miosis), and sinking of the eyeball (Enophthalmos).
Aside from cancer general symptoms such as malaise, fever, weight loss and fatigue, Pancoast tumour can include a complete Horner's syndrome in severe cases: miosis (constriction of the pupils), anhidrosis (lack of sweating), ptosis (drooping of the eyelid) and enophthalmos (sunken eyeball).