Cancer of Unknown Primary Presenting as Isolated FDG-Avid Cervical Lymph Node Metastasis: Diagnostic Escalation after...

Cancer of unknown primary (CUP) remains a diagnostic and therapeutic challenge, particularly when presenting as isolated cervical lymph node disease. Adequate tissue sampling is crucial, and escalation to excisional biopsy may be necessary when minimally invasive procedures are inconclusive.

A 62-year-old man with a history of long-term tobacco use presented with a right-sided neck mass. Otolaryngologic examination and fiberoscopy revealed no mucosal abnormalities. Fine-needle aspiration suggested metastatic poorly differentiated carcinoma, while core needle biopsy yielded scant, nondiagnostic material. Contrast-enhanced CT demonstrated pathological right cervical lymph nodes (level III 29 × 29 mm, level IIa 20 × 15 mm). 18F-Fluorodeoxyglucose positron emission tomography/computed tomography showed an FDG-avid right cervical nodal package at the level IIB/III border (SUVmax 21.1) and an incidental focal uptake in the left thyroid lobe (SUVmax 4.4), with no other suspicious lesions. Thyroid ultrasound revealed a small, well-demarcated hypoechoic lesion (3.5 × 2.6 × 4.5 mm); repeated ultrasound-guided FNAC was benign (Bethesda II), and calcitonin was within the reference range. The patient underwent excisional lymph node biopsy and comprehensive endoscopic evaluation under general anesthesia (panendoscopy with bilateral tonsillectomy and directed biopsies), without identification of a primary tumor. Histopathology and immunohistochemistry confirmed nodal metastasis of undifferentiated carcinoma, most consistent with carcinoma with sarcomatoid features, confined within the lymph node capsule. Because no primary site was identified after imaging, endoscopic evaluation, thyroid workup, and histopathological assessment of the lymph node, the diagnosis remained CUP. The patient was subsequently referred for radiotherapy.

In cervical lymph node metastasis from CUP, adequate tissue sampling remains essential for definitive diagnosis. When fine-needle aspiration suggests malignancy but core needle biopsy is nondiagnostic, early excisional biopsy should be considered to enable reliable histopathological and immunohistochemical classification. PET/CT may guide the diagnostic pathway and identify incidental findings requiring verification, but imaging should not delay escalation to representative tissue sampling.