Transforming growth factor beta (TGFbeta) plays an important role in cancer, but accurate measurement of circulating TGFbeta is complicated by the high TGFbeta content of platelets which can release TGFbeta ex vivo. We evaluated the use of citrate-theophylline-adenosine-dipyridamole (CTAD) tubes to reduce preanalytical variation in TGFbeta measurements caused by ex vivo platelet activation. CTAD substantially reduced ex vivo platelet activation relative to traditional plasma collections in normal donors, which correlated with a decrease in measured TGFbeta levels. We show that TGFbeta levels are elevated in the majority of cancer patients with skeletal metastases, and that within-patient variability of these levels is relatively low over several weeks. Patients with elevated TGFbeta could be subdivided into groups with or without evidence of platelet contribution to measured TGFbeta levels. The use of CTAD tubes allows a better determination of a patient's TGFbeta status, and may improve classification of patients with oncologic disease.
Keywords: CTAD; TGFβ; biomarker; cancer.