<s>[INST] context: (a) Source: GAS 888-889; GA 108-109Miosis, partial ptosis, and anhydrosis are a clinically important constellation of symptoms possibly indicating Horner syndrome. Horner syndrome is a lesion of the cervical sympathetic chain and sympathetic chain ganglia and is often a result of a Pancoast tumor, also known as a superior pulmonary sulcus tumor of the apex of the lung. The pupil, eyelid (superior tarsal muscle), and sweat glands are all under sympathetic nervous system control. The arch of the aorta and phrenic nerve are not part of the autonomic nervous system. The vagus nerve does carry parasympathetic fibers to muscles of the trachea, bronchi, digestive tract, and heart but not to any structure in the head and neck (laryngeal supply, and Von Ebner's glands in the tongue). A lesion to the phrenic nerve would result in paralysis of the diaphragm. The cardiopulmonary nerves are splanchnic nerves that are postganglionic and sympathetic. They originate in cervical and upper thoracic ganglia and innervate the thoracic cavity. The cardiopulmonary plexus is the autonomic supply to the heart. [/INST] question: A 45-year-old woman is admitted to the hospital with severe dyspnea. Radiographic examination confirms the presence of a Pancoast tumor. Physical examination reveals that the patient has miosis of the pupil, partial ptosis of the eyelid, and anhydrosis of the face. Which of the following structures has most likely been injured? | options: A: Sympathetic chain B: Vagus nerve C: Phrenic nerve D: Arch of aorta | answer: A </s>