Seems there is a lot more, and growing, support for the
CTC test. Again...larger swings may be more indicative. But you won't know unless you have results to compare. Could be one of a number of factors that gives a heads up. Even if lacking in nuance, the serum her2 could also be helpful if number was extreme.
Regarding biopsy, even different locations within the same tumor can give slightly different results. More stringent guidelines for processing time of paraffin slides have recently been suggested as important to results. Methinks too many variables make a 4 year old pathology less relevant, and perhaps misleading.
Treatments themselves seem to change the tumor behavior/pathology. Might be wise to make sure insurance issues aren't clouding diagnostic choices.