In line with many other examples in which biomarkers have a predictive value for individualized therapy strategies, such as steroid hormone expression in breast cancer or mutational analysis of tyrosine kinases in numerous tumor entities, malignant PEComas, too, should be examined for biomarkers that indicate an increased mTOR activity to obtain a scientific robust rationale to start mTOR inhibition therapy. This evidence concerns the gene MTOR and breast cancer.