The diagnosis of an occult primary tumor is made only if no primary tumor is detected after careful search and does not appear during therapy. Patients with cervical lymph node metastases histologically related to a previously treated primary tumor and patients with lymphomas and adenocarcinoma are excluded. If the biopsy is an undifferentiated carcinoma (in particular, a lymphoepithelioma), the most probable primary site is in Waldeyer ring; for example, the nasopharynx, base of tongue, or tonsil. Most epidermoid carcinomas metastatic to lymph nodes of the upper half of the neck will originate from a head and neck primary site. Squamous carcinomas metastatic to the lower neck may represent a primary site in the head and neck, esophagus, lung, or genitourinary tract. A search for primaries in these areas must be undertaken before assuming that the primary is occult. Primary tumors arising in the nasopharynx may be secondary to Epstein-Barr Virus (EBV) infection, and EBV genomic material may be detectable in cervical nodal tissue after DNA amplification using the polymerase chain reaction. Such a finding should lead to an in-depth search for a primary in the nasopharynx.
The extent of investigation and type of treatment must be individualized depending on the patient's age and wishes, and on the site, histology, and extent of metastatic lymph node involvement of the tumor. When a patient qualifies as having squamous carcinoma of the neck with occult primary, he or she should be checked for other obvious metastatic disease, such as lung, liver, or bone, since this would affect the locoregional approach to therapy.
Three-year, disease-free survival rates following surgery and/or radiation therapy for unknown squamous primaries range from 40% to 50% in patients with N1 disease to 38% and 26% for patients with N2 and N3 disease, respectively. Patients who later develop primary lesions have poor survival rates compared to those patients whose primaries remain occult, for example 30% versus 60%.
Patients with neck metastases from an undetectable primary should be given the benefit of definitive treatment. Despite the ominous situation of an undiscovered primary, a significant number of patients do achieve cure by both surgical and radiotherapeutic approaches. In some patients, long-term repeat examinations will eventually disclose the primary tumor, and at a treatable stage.
Feinmesser R, Miyazaki I, Cheung R, et al.: Diagnosis of nasopharyngeal carcinoma by DNA amplification of tissue obtained by fine-needle aspiration. N Engl J Med 326 (1): 17-21, 1992.
de Braud F, al-Sarraf M: Diagnosis and management of squamous cell carcinoma of unknown primary tumor site of the neck. Semin Oncol 20 (3): 273-8, 1993.