pet scan shows activity five weeks after oxi and 5FU Push

My son last fall had 6weeks radiation and six weeks 5 Fu Push then re-section, a month later a reversal of the illy and then four months oxi every other week ending in March.
The Onc Dr said she feels he is cured. Four weeks later he has the port removed. Just a couple of weeks later he has had a Pet Scan ( last Monday. The surgeon calls a week later and wants to do a sigmoidoscopy on Wed, May 5. He was told a week ago he has a tear (a guess a fissure). The surgeon stated that it is very early to be showing activity. Could this be inflamation from being constipated? Help. I believe that our prayers have shown us that he truely healed. What do you all think?