A 65 year old man presents with significant weight loss and complains of cough, SOB and chest pain. Exam: left pupil constricted, drooping of left eyelid. What is the most likely diagnosis?

The key is A. Pancoast tumor. [Pancoast tumour is the apical lung cancer that is associated with destructive lesions of the thoracic inlet and involvement of the brachial plexus and cervical sympathetic nerves (the stellate ganglion) leading to horner’s syndrome].