Tumour Thrombus in Non-Classical Malignancies: A Multitracer PET/ CT Case Series

Tumour thrombus (TT) indicates intravascular extension of tumour into adjacent blood vessels, which is particularly common with renal, adrenocortical carcinoma and hepatocellular carcinomas. The presence of TT indicates an advanced disease course, markedly worsening the prognosis and impacting treatment approach in most malignancies. Differentiation of TT from bland thrombus remains a critical diagnostic challenge on conventional imaging, particularly when intravascular filling defects occur within major vessels. In this case series, we illustrate the complementary role of positron emission tomography/computed tomography (PET/CT) using multiple radiotracers in accurately characterising TT across diverse malignancies. Increased radiotracer uptake within intraluminal filling defects associated with vessel expansion on PET/CT enabled confident distinction of TT from bland thrombus using 18 F-FDG, 68 Ga-DOTATATE, and 68 Ga-FAPI. Histopathological confirmation of intravascular tumour extension is often impractical due to the location of thrombi within critical vascular structures, including the portal vein, inferior vena cava, renal vein, and cardiac chambers. In this context, multitracer PET/CT serves as a robust, non-invasive alternative, offering whole-body assessment of disease burden, accurate staging, and meaningful impact on clinical decision-making. This case series highlights the expanding role of molecular imaging in the detection and characterisation of TT in malignancies with a traditionally low incidence of vascular invasion.