My last CA 27-29 was 625 and they still can’t find any new cancer so not sure how great a test this is

The tumor markers can respond to all kinds of things in the body, especially inflammation. A rise in the test result does not necessarily mean that there is cancer activity. My oncologist includes the blood test along with others because a rise in the number, especially a continuing upward rise, might reflect cancer so can be an early warning signal. And a decrease or no-change is good. But, for example, my cardiologist discounts the CRP test can indicate inflammation in the body because there myriad possible reasons for non-significant inflammation. He told me dieting or any significant change in eating patterns can trigger temporary inflammation of no importance.

Having noted that, there are people who've posted on Mayo Connect that their lives were saved because elevated tumor markers were the only sign that a cancer might have recurred. So I'm glad that my oncologist tracks the results because more data is better than less I think.

Had pet scan, cancer cell search, bone scan, brain MRI and CT chest and abdomen

I have or they told me I have node recurring breast cancer but ca27/29 is 9...!!!!

The tumor marker test is imperfect in that markers things other than cancers can cause the number to rise and not all cancers trigger an increase. Some doctors don't have them done at all because of that though mine includes them because a rise in the result can merit attention. But as @dianemh can testify, finding the reason for the rising number isn't always clear either.

Did they find anything?