Diagnostic performance of fine-needle aspiration in soft tissue tumors: Application of the World Health Organization System for Reporting Soft Tissue Cytopathology and risk of malignancy assessment.

Background: Recently, a new World Health Organization Reporting System for Soft Tissue Cytopathology (WHO System) was introduced. To analyze the value of this system, routine fine-needle aspiration soft tissue tumor (STT) cases were reviewed.

Methods: Cytology samples of STTs collected between 1954 and 2022 at the Institut Curie were used (2214 cases, including 1376 primary tumors). All specimens were classified according to the predominant cytomorphological pattern and the WHO System. The diagnostic accuracy and risk of malignancy (ROM) in each category were calculated.

Results: Final diagnoses revealed 1236 malignancies and 978 benign or low-risk tumors. The original cytological evaluation led to 21 false-negative results (0.85%) and 29 false-positive results (1.17%). Sensitivity, specificity, positive predictive value, and negative predictive value were 98.3%, 92.1%, 97.5%, and 94.2%, respectively. Overall diagnostic accuracy was 94.2%. The ROM calculated according to the WHO System was 29.87%, 2.49%, 39.62%, 51.43%, 68.42%, and 97.69% in the nondiagnostic, benign, atypical, soft tissue neoplasm of uncertain malignant potential, suspicious for malignancy, and malignant categories, respectively; however, it varied broadly depending on the morphological pattern (62.78% in spindle cell tumors, 84.58% in myxoid tumors, 3.00% in lipomatous tumors, 78.15% in epithelioid tumors, 94.26% in pleomorphic tumors, and 100% in round cell tumors).

Conclusions: Cytology of STTs is a powerful diagnostic method. Some cytological patterns overlap in different morphological groups, and the possibility of false-negative and false-positive diagnoses may persist. This analysis evidenced utility of the WHO System, especially when combined with morphological pattern assessment. Subclassification in particular diagnostic categories allowed for calculation of the ROM, which is crucial for optimal patient management.