A Rare Case of Metastatic Extragonadal Yolk Sac Tumor – A Challenging Diagnosis on Cytomorphology

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Abstract Introduction/Objective Yolk sac tumors are characterized by variable histologic patterns and broad cytologic spectrum; thereby making the distinction from a poorly differentiated adenocarcinoma in a metastatic site extremely challenging. We present cytology and histology of a metastatic extragonadal germ cell tumor with predominant solid yolk sac component. Methods/Case Report 36-year-old male presented with bilateral supraclavicular masses (right: 6 x 7 cm, left: 3 x 4 cm). CT chest and abdomen revealed large mediastinal and hilar nodal mass (11.6 cm), right hilar mass (8.5 cm), bilateral heterogeneous adrenal masses (right: 11.4 cm, left: 3.1 cm), and an enhancing retroperitoneal implant. Differential diagnoses of lymphoma, adrenocortical carcinoma, small cell lung carcinoma, and metastatic germ cell tumor were considered. Testicular ultrasound revealed no masses. Fine needle aspiration of supraclavicular lymph nodes showed highly cellular smears comprised of tumor cells, dispersed singly and in clusters, with irregular nuclear contours, increased nuclear to cytoplasmic ratio, coarse chromatin, occasional prominent nucleoli, and vacuolated cytoplasm. Tumor cells were positive for KRT7 and TTF-1, and negative for p40 and PAX8. A diagnosis of metastatic poorly differentiated carcinoma was rendered. Subsequent excisional biopsy of the lymph node showed a metastatic tumor with tumor cells similar to those seen in cytology, appearing in solid sheets with focal papillary architecture, replacing the entire lymph node. Additional immunohistochemistry showed expression of SALL4, Glypican 3, with lack of expression for OCT3/4, AFP, hCG, and CD30, supporting the diagnosis of metastatic yolk sac tumor, solid pattern. Results (if a Case Study enter NA) NA. Conclusion Aggressive clinical presentation, broad clinical differential diagnoses, rarity of a primary mediastinal yolk sac tumor, non-diagnostic cytomorphology along with expression of divergent differentiation markers (TTF-1 in our case) makes a definitive diagnosis of metastatic extragonadal yolk sac tumor extremely challenging. High index of clinical suspicion is required for a definitive diagnosis on cytomorphology.