Soft tissue sarcomas: pattern diagnosis or entity?

Soft tissue sarcomas (STS) are a diverse and heterogeneous group of tumours. The sub-classification of these tumours is of importance for both prognosis and treatment. Classically, sub-categorization is based purely on histomorphological grounds, but as new techniques evolve, a more conclusive and accurate diagnosis can be made. This study describes the prevalence of soft tissue sarcomas in adults diagnosed at The Aga Khan University Hospital (AKUH) and the impact of immunohistochemistry (IHC) on the precise sub-categorization of these tumours. The study included 364 adults (age 16+) who were diagnosed as soft tissue sarcoma in the past six years (May 1991-July 1997) at the Histopathology lab of the AKUH. Where indicated, tumours were stained with a panel of antibodies using the PAP technique. Of these, 237 (65%) were male and 127 (35%) were female. The median age at which all sarcomas were diagnosed was 39.5 years. The most common site was the lower extremity (29%). The most frequently diagnosed sarcoma was leiomyosarcoma (13%), followed by malignant nerve sheath tumour (12%), rhabdomyosarcoma (10%) and liposarcoma (10%). Cases were further analyzed by dividing them into two groups, each group comprised of all sarcomas diagnosed during the specified period. In the period 1991-1994, only 16% of cases were further analyzed using IHC, while in the period 1995-1997, IHC was performed on 59% of cases. In the 1991-1994 group, a conclusive diagnosis was made in 57% of the cases and in the 1995-1997 group in 78%. A Chi-square test was performed, which proved that these results were statistically significant. Soft tissue sarcoma is one of the key areas in surgical pathology where immunohistochemistry plays an important role in both precise diagnosis and sub-categorization.