Cytologic-histologic correlation of musculoskeletal lesions: examination of the proposed World Health Organization Reporting System for Soft Tissue Cytopathology

Introduction: In June 2019, the World Health Organization Reporting System for Soft Tissue Cytopathology (WHORSSTC) was proposed at the European Congress of Cytology in Malmö, Sweden, for reporting soft tissue cytology. In this retrospective review, we evaluate the diagnostic categories of the proposed WHORSSTC. Materials and methods: Five hundred ninety-two fine needle aspiration cytology and touch preparation specimens from core needle biopsies from musculoskeletal lesions were identified (2015–2021), of which 62 cases (10%) had an associated surgical resection. Of these cases, 15 cases with resection were diagnosed with fine needle aspiration, and 47 cases with resection were diagnosed with touch preparation samples. Cytology specimens were reclassified into the proposed WHORSSTC Categories: I) nondiagnostic/unsatisfactory, II) benign, III) atypical, IV) soft tissue neoplasm of uncertain malignant potential, V) suspicious for malignancy, and VI) malignant. The rate of malignancy was calculated based on corresponding surgical resections where a malignant resection diagnosis was considered a positive result. Results: The observed rate of malignancy within the tested categories were as follows: Category I: nondiagnostic (5/17, 29%), Category II: benign (1/14, 7%), Category III: atypical (0/2, 0%), Category IV: soft tissue neoplasm of uncertain malignant potential (7/10, 70%), Category V: suspicious for malignancy (1/1, 100%), and Category VI: malignant (18/18, 100%). Our study showed a sensitivity of 96%, a specificity of 83%, a positive predictive value of 90%, and a negative predictive value of 94%. Conclusions: Our results support the potential utility of a standardized soft tissue reporting system for cytology to improve the clinical management of patients.