In addition to the epithelial tumors of the nasopharynx, cancers of the nasopharynx can also originate from minor salivary glands, most commonly adenoid cystic and mucoepidermoid carcinomas. Cancer of unknown primary of the head and neck represents 1% to 4% of patients with malignant tumors of the head and neck and is diagnosed after identification of metastatic lymphadenopathy in which no primary is evident [9]. When the pathology is positive for EBV, the primary site is presumed to localize to the nasopharynx. Patients often present with a neck mass or findings secondary to local invasion of structures, with symptoms such as epistaxis or nasal blockage, hearing loss secondary to Eustachian tube dysfunction, or findings of cranial nerve involvement [76]. Advanced local disease in NPC is common at presentation with skull base involvement in 25% to 35% of cases and intracranial invasion in 3% to 12% of cases [77]. Accurate staging of the primary tumor includes evaluation of involvement of osseous structures, including the skull base and extension into the adjacent soft issues such as the pterygoid musculature, which are upstaging features. NPC has a high rate of regional nodal disease at presentation, including retropharyngeal and cervical lymph nodes, with as many as 75.8% of patients presenting with nodal mass at initial presentation [78]. Identification of nodal disease is critical in staging because it confers decreased survival, and the presence of nodal disease or advanced local disease is associated with increased risk for distant metastases. NPC also has a relatively high rate of distant metastases compared with other head and neck cancers, and distant metastases are found in 5% to 11% of patients at the time of diagnosis. The most common sites of metastasis are bone (20%), lung (13%), and liver (9%) [79,80].
Staging and Post Therapy Assessment of Head and Neck Cancer. In addition to the epithelial tumors of the nasopharynx, cancers of the nasopharynx can also originate from minor salivary glands, most commonly adenoid cystic and mucoepidermoid carcinomas. Cancer of unknown primary of the head and neck represents 1% to 4% of patients with malignant tumors of the head and neck and is diagnosed after identification of metastatic lymphadenopathy in which no primary is evident [9]. When the pathology is positive for EBV, the primary site is presumed to localize to the nasopharynx. Patients often present with a neck mass or findings secondary to local invasion of structures, with symptoms such as epistaxis or nasal blockage, hearing loss secondary to Eustachian tube dysfunction, or findings of cranial nerve involvement [76]. Advanced local disease in NPC is common at presentation with skull base involvement in 25% to 35% of cases and intracranial invasion in 3% to 12% of cases [77]. Accurate staging of the primary tumor includes evaluation of involvement of osseous structures, including the skull base and extension into the adjacent soft issues such as the pterygoid musculature, which are upstaging features. NPC has a high rate of regional nodal disease at presentation, including retropharyngeal and cervical lymph nodes, with as many as 75.8% of patients presenting with nodal mass at initial presentation [78]. Identification of nodal disease is critical in staging because it confers decreased survival, and the presence of nodal disease or advanced local disease is associated with increased risk for distant metastases. NPC also has a relatively high rate of distant metastases compared with other head and neck cancers, and distant metastases are found in 5% to 11% of patients at the time of diagnosis. The most common sites of metastasis are bone (20%), lung (13%), and liver (9%) [79,80].