Although caspase-9 are executors of apoptosis, little is known of their prognostic value in primary tumours. Irisflorentin Expression of cleaved caspase-9 protein correlates with a longer OS in patients with Hodgkin��s lymphoma, although the clinical significance of low caspase-9 expression in colon carcinoma, medulloblastoma and gastric carcinoma remains unclear. Expression of caspase-10 is also low in gastric carcinoma, rectal and colorectal cancers. The aims of this study were to examine PI, AI and expression of caspases-8, -9 and -10 in a panel of primary ESFT to evaluate and compare their prognostic power. An investigation was carried out into the optimal cut-point choice for PI. PI was investigated as a continuous 3-Cyano-7-ethoxycoumarin covariate within a Cox model; the log-rank value was calculated over the whole range of cut-points to visualise any patterns, and the cut-point log rank values were compared to those when the data is described as a continuous covariate. Fractional polynomials were calculated to investigate how the data could best be described as a continuous covariate, using a series of predefined transformations of predictor variables. If the cut-point describes the data significantly better than a fitted model, it is likely that the cut-point effect is real; otherwise the survival may be related to the PI on a continuous scale. The number of apoptotic cells was low in the majority of primary ESFT, and AI did not predict prognosis in the univariate or multivariate models. This is the first study to describe this relationship in ESFT. AI has been correlated with survival in other cancers with contradictory findings, however analysis has been based values above and below cut points rather than as a continuous variable. An increase in AI in tumours posttreatment may be a useful surrogate tumour marker of response to chemotherapy. For example, AI has been shown to correlate with pathological response in breast cancer biopsies collected after therapy. Some studies have suggested that immunohistochemistry for cleaved caspase-3 might replace measures of apoptosis such as TUNEL, and absence or low numbers of cleaved caspase-3 positive cells have been associated with a worse prognosis in patients with nasopharyngeal carcinoma and glioma.