Fine-needle aspiration biopsy of growing teratoma syndrome as a diagnostic pitfall of metastatic adenocarcinoma

Growing teratoma syndrome (GTS) is a rare clinical entity that can occur in patients with a history of treatment for germ cell tumors (GCTs) and normalized serum tumor markers. Owing to the assortment of tissue types found in teratomas that may exhibit atypical features, distinguishing GTS from metastatic cancer in extragonadal masses can be challenging. Fine-needle aspiration biopsy (FNAB) can be useful for the rapid diagnosis of metastatic masses and has been effective in distinguishing GCTs from one another. However, discrepancies in cytologic and histologic diagnoses have been reported in the evaluation of GCTs by FNAB. The potential incomplete sampling of metastatic teratomas in GTS by FNAB along with features of cellular atypia commonly found in teratomas can lead to a misdiagnosis of metastatic carcinoma and drastically affect treatment. Correlation of cytologic, histologic, clinical, and radiographic findings are essential in evaluating metastatic masses in patients with a history of GCT. We report a case of a 46-year-old man with GTS originally diagnosed on FNAB as metastatic adenocarcinoma compatible with a colorectal primary tumor.