Evaluating Fine Needle Aspiration Cytology for Diagnostics of Soft Tissue and Bone Tumours.

OBJECTIVE: There is a wide spectrum of tumour and tumour-like lesions in soft tissue and bone. Fine needle aspiration cytology (FNAC) is a cheap and accessible method that can provide a rapid diagnosis in most instances. We have evaluated the usefulness of FNAC for bone and soft tissue lesions at the Karolinska University Hospital, and we have identified diagnostic pitfalls for FNAC when compared to histopathology. METHODS: Between 2018 and 2019, 503 patients with FNAC and corresponding histopathological specimens were identified using digital pathology records. The pathology reports were manually studied and compared. All soft tissue FNACs were reclassified according to the WHO Reporting System for Soft Tissue Cytopathology and risk of malignancy (ROM) was calculated. RESULTS: FNAC correctly predicted malignancy in 85% of the samples. The sensitivity and specificity of detecting malignancy were 89% and 93% for soft tissue lesions, and 87% and 100% for bone lesions. Correspondingly, the PPV and NPV were 94% and 88% in soft tissue, and 100% and 83% in bone. Non-representative sampling was the most important factor for missing malignancy. CONCLUSION: In the right hands, FNAC is a useful method for diagnosing soft tissue and bone lesions. Its primary use should be to initiate and guide further care rather than provide an exact subtype in a preoperative setting. The limitations of negative FNACs need to be clearly communicated in pathology reports and multidisciplinary conferences to achieve safe tumour investigations.