Proliferative activity (MIB‐1 index) is an independent prognostic parameter in patients with high‐grade soft tissue sarcomas of subtypes other than malignant fibrous histiocytomas: a retrospective immunohistological study including 216 soft tissue sarcomas

AIMS: To evaluate the prognostic value of tumour proliferative activity, p53 accumulation and bcl-2 expression in a retrospective series of 216 patients with soft tissue sarcomas (STS). METHODS AND RESULTS: The immunohistochemical analyses were performed on formalin-fixed, paraffin-embedded tissue. The proliferative activity was assessed by use of the monoclonal antibody MIB-1 and evaluated in multiple, random systematic sampled fields of vision. The percentage of proliferating cells (the MIB-1 index) ranged between 1% and 85% (median 12%). A significant increase in mean MIB-1 index was seen with increasing histological malignancy grade. Variation in the incidence of p53 accumulation and bcl-2 positivity among different histological subtypes was observed. p53 accumulation was frequent in synovial sarcomas and leiomyo- and rhabdomyosarcomas, whereas bcl-2 preferentially was expressed in synovial sarcomas. Univariate analysis identified patient age, tumour size, histological grade of malignancy, MIB-1 index and p53 accumulation as significant prognostic parameters. Multivariate Cox analysis, including tests for interaction terms between histological subtypes and MIB-1 index, showed independent prognostic effect of MIB-1 index and tumour size in patients with high-grade tumours of other subtypes than malignant fibrous histiocytoma (MFH). CONCLUSIONS: Histopathological malignancy grading is the most important single prognostic factor for overall survival in STS, but estimation of MIB-1 index is useful for identifying the least favourable subgroup of high grade STS of other subtypes than MFH, for whom adjuvant therapy may be indicated.