low ca 27,29

DX: invasive duct carcinoma, 2.5cm tumor.  Neg node, neg hormone recpt, neg her2, grade 3, intermediate vascu invasion.
Treatment: 4ac, 4 taxol followed by radiation.
Ca27.29 was 16.8 at the end of chemo.  One year 4mos after the end of treatment it is 3.5 (or less as it can not be measured at less than 3.5).  Can it be assumed that all cancer cells are gone since the antigen can not be measured?  Do cancer cells ever return from a near 0 score?

[CCF-RN,MSN-rf]

Dear honeybee:  There is much controversy over the use of the CA27.29 tumor marker.  We do not use this test at our institution.  You have had appropriate adjuvant therapy.  I would assume, based on this, that you are currently free of disease.  Unfortunately, there is no guarantee that this cancer will not return.  You have early stage disease - and that is good.  The longer you are disease free, the better.  You have a very good chance of beating this long term.