Ewing's sarcoma. A retrospective study of histological and immunohistochemical factors and their relation to prognosis.

Histological and immunohistochemical features of 87 patients with conventionally diagnosed Ewing's sarcoma were studied retrospectively on routinely processed material and evaluated with regard to prognostic significance. 74% were convincingly positive when stained for vimentin, 13% were doubtful, and 13% were negative. A varying degree of positivity for neuron-specific enolase (NSE) was found in 15%; these cases all co-expressed vimentin. A single tumour contained scattered cytokeratin-positive cells. Positivity for the leukocyte common antigen (LCA) could be demonstrated in three cases; these were excluded from the statistical analysis of prognostic factors. Growth pattern, soft tissue invasion, monomorphic or dimorphic cell population, and PAS-, NSE- or vimentin-positivity did not influence survival significantly. However, prognosis was increasingly poor with increasing degree of necrosis: median survival was 28 months for grade I necrosis (less than 10%), 16 months for grade II (10-50%), and 11 months for grade III (greater than 50%), p less than 0.0005. A mitosis count of less than 1 per high-powerfield (HPF) was correlated to a median survival of 26 months, greater than or equal to 1 per HPF to 12 months, p less than 0.05. The findings indicate some degree of heterogeneity in Ewing's sarcoma which may be related to primitive peripheral neuroectodermal tumours (PNETs), or be a true blastoma. In future trials, diagnostic criteria (including immunohistochemistry) should be clearly defined and materials should be large enough to allow for stratification according to prognostic factors.