الفهرس 
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Abstract
CRC is the third most common malignancy. Up to 60% of all patients diagnosed with CRC eventually develop metastases with approximately 90% had un-resectable liver metastases, and about 20-30% had metastatic diseases at the time of diagnosis. With new era of development of targeted therapy, the overall survival rate has been increased. Assessment of therapeutic response is of great concern especially with targeted therapy which are cytostatic agents, had limited affection on size yet dominant affection on metabolic activity.So, 18F-FDG PET/CT is believed to be more informative for the evaluation of treatment response than conventional radiological imaging (CT and /or MRI). Most studies assessing response of mCRC patients either early after one cycle or delayed after 3 cycles of chemotherapy ± target therapy, and comparing metabolic response with CT based response criteria and shown superiority and accuracy of PET/CT based metabolic response criteria on the morphological criteria that is beneficial for the patients for selecting who will complete or not complete to these agents, subsequently avoiding un-needed expensive drugs and its toxicity. KRAS molecular testing is currently the trend before using these targeted agents as it determines the candidate patients who will benefit from these drugs. Few studies with contradictory results comparing the KRAS status and quantitative parameters extracted from PET/CT either for the primary CRC or the metastatic lesions to act as a non-invasive biomarker for these patients especially with special hard circumstances causing difficulty to determine the molecular status. Limited data about the association between KRAS status and metabolic response of these patients. In our study, we compared PET/CT based metabolic response using EORTC criteria and CT based morphological criteria using RECIST1.1 and found a high statistical significant difference regarding EORTC response to re-classify the SD either to PMD or to less extent PMR We found that pulmonary metastasis is the worrying metastatic site which needs an extensive therapeutic management. We also compared the association between KRAS status and quantitative parameters extracted from PET/CT and we found that patients with mutant type has a higher mean tumour SUVmax rather than patients with wild type, however with no statistical significance. Finally we found a significant association between tumour marker level and DCR based on metabolic response and also PET/CT quantitative parameters (TLG and MTV). In conclusion, this work demonstrated the utmost role and superiority of 18F-FDG PET/CT in response assessment of mCRC patients receiving chemotherapy± target therapy compared to conventional radiological imaging (CT).