Your TSH can go up for other reasons other than the return of cancer. All this means is that your patuitary gland (spelling) is not getting the proper amount of T3 hormone. This can be due to a few factors such as inadequate medication or a conflict with other meds. Are you taking your meds on at a regular time daily, and on an empty stomach? Are you taking other meds? have you changed your diet lately? Have you lost weight lately? Maybe its just your body becoming adjusted to the levels of your meds and you will just need to re-adjust. Did they check your TG level. That is the true test for cancer reaccurance, not TSH. Get that check before worrying.
Take care
Sancho