• Variably cohesive groups of uniform, moderately pleomorphic malignant cells

• Singly dispersed malignant cells are seen.

• The malignant cells have vesicular, occasionally eccentric nuclei, prominent nucleoli and generally scant cytoplasm.
• Smaller lymphocytes are seen in the background.
• No granulomas or necrosis present.

Diagnostic considerations at this point

• Metastatic poorly differentiated/undifferentiated carcinoma
• Non-Hodgkin lymphoma with medium to large cell morphology
• Metastatic melanoma

• Cell block shows singly scattered and very small clusters of tumour cells.

• The tumour cells are positive for AE1/3.

Nasoendoscopy shows diffuse postnasal space irregular prominence extending to bilateral fossa of Rosenmuller. A biopsy of the left postnasal space was taken and shows the following:

• Diffuse sheets of tumour cells with crush artefact

• The better-preserved tumour cells show enlarged and irregular vesicular nuclei, prominent nucleoli and scant cytoplasm.
• Admixed lymphocytes are seen.

• The tumour is positive for AE1/3 and EBER-ISH (as shown above).
• It is also positive for CAM5.2 and CD99 (the latter showing only cytoplasmic staining with no diffuse strong membranous staining).
• The tumour is negative for CD3, CD20, p63, p40, synaptophysin, chromogranin, CD56, S100, desmin and NUT1. INI1 is retained.

Diagnosis

Left postnasal space, biopsy: Non-keratinizing (nasopharyngeal) carcinoma, undifferentiated type (EBER-ISH positive)

• The tumour cells in the cervical lymph node FNA morphologically resemble those seen in the postnasal space biopsy.
• Like the postnasal space tumour, the tumour cells in the cervical lymph node FNA are also AE1/3 positive.

DIAGNOSIS

Left level II cervical lymph node, FNA:

Poorly differentiated/undifferentiated malignant cells present, compatible with metastatic non-keratinizing (nasopharyngeal) carcinoma, undifferentiated subtype