Fine needle aspiration cytology of metastatic carcinomas with papillary architecture: A systemic assessment of clinical, cytological and immunohistochemical parameters

Background Papillary structures are frequently encountered in metastatic carcinomas from various organs and tumours of different histotypes. This study aims to investigate the predictive value of fine needle aspiration cytology (FNAC), immunohistochemistry (IHC) and the clinical parameters which can be examined in the assessment of the primary sites of metastatic carcinomas with papillary architecture. Methods FNAC samples of metastatic carcinomas with papillary architecture were evaluated for overall cellularity, epithelial cohesion, background features, papillary architecture, cytology and IHC. The corresponding clinical information was also reviewed. Results A total of 130 cases were included. The most common primary sites were thyroid (38.5%), lung (30.8%) and gynecological organs (22.3%); the others were pancreaticobiliary, urothelial, colorectal, and esophageal. Age (P = 0.039), biopsy site (P < 0.001) and laterality (P = 0.006) correlated with primary site. Papillary structures were confirmed on biopsy/excision of most cases (n = 85/87, 97.7%). Thyroid primaries exhibited broad papillary stalks, thin lining epithelium, fewer epithelial polymorphs, and the presence of background giant cells and histiocytes (P = 0.021- < 0.001). Low-grade cytological features, nuclear grooves and inclusions (P < 0.001) were seen in thyroid primaries. High-grade features (P < 0.001-0.49), multinucleated tumour cells, apoptotic bodies and mitoses (P < 0.001-0.49) were more common in lung/gynecological primaries. Multivariate analysis identified nuclear/cytoplasmic ratio, chromatin character, the presence of nuclear grooves and mitosis as independent features (P = 0.001-0.024). TTF1/TGB/PAX8 panel results showed good agreement with the cytological assessment and site of primary. Conclusion Papillary structures and cytological features are reproducible in FNAC assessment of metastases and their corresponding primary sites. Cytological features, IHC and clinical information are invaluable in determining the primary site.