My wife Tammy has also had several blood clots due to her CC. They were in the area around the portal vein, and 2 other areas as well. This caused her a great deal of discomfort and helped the doctors diagnosis her CC. She has been on Fragmin every day since February 2007. Once they got the situation under control, (about 2 weeks), the pain has subsided. Her body created many hundreds of extra pathways for the blood to travel and this is causing additional difficulty to see the area around the portal vein and the actual area of the CC tumor. Just a few weeks ago she had to go for a special test (Contrast Enhanced Ultrasound), where they inject air bubbles into her veins so they stand out on an ultrasound.
I understand that this is quite common with CC as well.