GPT and cancer: Although this approach sounds appealing, it should be noted that only 45% of ATRX-deficient STSs appear to be ALT positive, while only 55% of ALT-positive tumour are ATRX deficient.63 Furthermore, certain malignant tumours also show no evidence of either telomerase or ALT activity, which in some series number up to 50% of STSs.16 These cases suggest that current assays are either not sensitive enough to detect telomerase or ALT in these tumours, or that a yet undiscovered TMM is activated.