Histopathological diagnoses in soft tissue tumours: an experience from a tertiary centre in Malaysia.

Soft tissue tumours are a group of remarkably diverse neoplasms that frequently pose significant diagnostic challenges to general pathologists. This study aimed to compare the agreement of histopathological diagnoses between general pathologists from various referral institutes and the referred soft tissue pathologist in a tertiary centre. The common discrepancies and their causes are also presented here. A retrospective study was conducted on 243 cases of potential soft tissue tumours referred to Hospital Kuala Lumpur, Malaysia over a period of 5 years. Reports by the referring pathologists and the soft tissue pathologist were compared based on tumour classification and tumour behaviour. Overall, there was moderate agreement in soft tissue tumour diagnoses in both tumour classification (weighted κ = 0.423) and tumour behavior (weighted κ = 0.548). The highest agreement of tumour classification was seen in the adipocytic tumours (21/28 cases), Ewing sarcoma (5/7 cases) and smooth-muscle tumours (3/5 cases). The highest rates of discrepancies were the so-called fibrohistiocytic tumours (7/11 cases), vascular tumours (9/15 cases) and undifferentiated/ unclassified sarcomas (19/32 cases). Full agreement for tumour behaviour was seen in 178 cases and there were 21 cases of zero agreement. Liposarcoma, alveolar soft part sarcoma and benign fibrous histiocytoma were the most frequent benign/malignant diagnostic discrepancies. The most common causes of discrepancy were wrong morphological interpretation followed by insufficient immunohistochemical stains performed. In conclusion, review of diagnosis by a pathologist specialized in soft tissue improves the quality of diagnosis in these heterogenous and rare tumours. A good panel of immunohistochemical stains with additional molecular study is crucial in the general hospital laboratories practice.