<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q: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 left upper 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 is the most likely site of the primary neoplasm in this patient?? A: Skin, B: Brain, C: Nerve sheath, D: Bone, E: Muscle,  <response>: This is a clinical vignette describing a 43-year-old man with weight loss and an enlarged, firm, immobile cervical lymph node that is positive for cytokeratin on biopsy. This indicates metastasis of a carcinoma to the cervical lymph node. Cytokeratin positivity suggests the primary tumor is of epithelial origin. The location in an upper cervical lymph node suggests drainage from the head and neck region. Of the choices given, skin cancer in the head and neck region e.g. squamous cell carcinoma would be the most likely primary site to metastasize to an upper cervical lymph node. Brain, nerve sheath, bone and muscle tumors are less likely to present with cervical lymphadenopathy.A: Skin 