A 43-year-old man comes to the physician because of weight

loss and swelling on the left side of his neck. Physical examination shows a

firm, enlarged cervical lymph node that is immobile. Immunohistochemical

testing performed on a biopsy specimen from the lymph node stains positive

for cytokeratin. Which of the following organ is the most likely site of

the primary cytokeratin-positive neoplasm in this patient?