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Purpose: Positron emission tomography (PET) has gained widespread use in cancer diagnosis and treatment, but how many malignant cells are required for a tumour to be detected by PET? Methods: Three human cancer cell lines [glioblastoma and two subtypes of small cell lung cancer (SCLC)] in concentrations from 104 to 107 were seeded on six-well plates or plastic tubes and treated with [18F]fluorodeoxyglucose (FDG) in vitro. FDG retention was measured in a PET/CT scanner and in a calibrated well counter. The clinical situation was simulated using a cylinder phantom with a background concentration of FDG. Results: The theoretical detection limit was found to be around 105 malignant cells. In a cylinder phantom the detection limit was increased by a factor of 10. The FDG retention by the glioblastoma cell line was significantly higher than the activity of the SCLC cell line. FDG retention measured by PET and a gamma counter was closely correlated to the number of cells and a linear relationship was found. Discussion: The detection limit of PET is in the magnitude of 105 to 106 malignant cells. The experimental set-up was robust and well suited as a platform for further investigations of factors influencing the detection limit of PET. [ABSTRACT FROM AUTHOR]

Here we integrated multiphoton laser scanning microscopy and the registration of second harmonic generation images of collagen fibers to overcome difficulties in tracking stromal cell-matrix interactions for several days in live mice. We show that the matrix-modifying hormone relaxin increased tumor-associated fibroblast (TAF) interaction with collagen fibers by stimulating β1-integrin activity, which is necessary for fiber remodeling by matrix metalloproteinases. [ABSTRACT FROM AUTHOR]