Unveiling Occult Nasopharyngeal (Undifferentiated) Carcinoma: A Case Series Highlighting the Worth of Fine-Needle Aspiration Cytology as a Frontline Diagnostic Tool for Hidden Lethal Malignancies

This series highlights the indispensable role of FNAC with a dual-stain approach and intricate diagnostic challenges in deciphering occult undifferentiated NPC. To the best of our knowledge, this is the first series to formally document a significant observation - stain-dependent cytologic shift in undifferentiated NPC: tumor cells appeared as dispersed with hyperchromatic homogeneously dark-stained naked nuclei mimicking lymphoma on May-Grünwald-Giemsa (MGG), but as loosely cohesive clusters or syncytial sheets with vesicular nuclei on Papanicolaou. MGG alone risks mimicking lymphoma, and Papanicolaou alone risks mimicking metastatic carcinoma. Such perplexing cytomorphological variations with two stains risk erroneous diagnoses, yet offer a unique clue to undifferentiated NPC. Thus, extensive cytologic sampling with dual-stain strategy enables early recognition of an aggressive, elusive, and often misdiagnosed malignancy, significantly improving survival in cases that would otherwise be fatal.