Seeing that the proliferation rate is preoperatively not determined without a biopsy (which is contraindicated due to dissemination), all patients with colorectal liver metastases (with no signs of extrahepatic deposits) are resected, without knowledge of the proliferation. FLT is a marker that visualizes proliferation and thus seems an ideal candidate to determine the proliferation rate in a noninvasive method. As of yet no validation studies of FLT-PET in colorectal liver metastases have been described.