[Lani]

The amount of cancer seen in the breast and the lymph nodes at the time of your surgery will be one way they tell if your treatment has worked--however, recent papers have shown that the absence of cancer seen at the time of surgery is less of a predictor of how you will do if your her2+ cancer is also ER+ than if it were also ER-/

That said, I have advocated previously for serial sampling of the bone marrow ie before and after treatment to see if disseminated cancer cells are there.
RESEARCHERS work seem to show that whether or not there are cells hiding out in the bone marrow after treatment has more to do with whether cancer returns than circulating tumor cells. Of course the former takes a marrow biopsy and the latter takes only a blood draw. Marrow biopsies are presently only done as part of clinical trials. I personally wish that would change, as I suspect there is a lot to discover earlier as to whether the treatments so far have worked and hopefully, changing/adding treatment if it has not will improve treatment results.

That said, you MIGHT be able to talk your doctor into a CTC test but there is only one FDA approved way to test and it may not be as accurate as other methods when all is said and done

Rest assured, at SABCS they repeatedly said her2+ breast cancer (early) has turned from one of the worst (with triple negative) to one of the best breast cancers to have. There are more and more and better drugs available and someday there may even be ways to detect a few residual cancer cells to tell if treatment did all they hope for (using supermagnetic iron nanoparticles fused or herceptin or herceptin affibodies) It is a work in progress and not all the "tricks" are available yet, but they are coming along much more quickly than in the past.

I am in no way qualified to give advice, being only well-read. I rarely voice opinions, except on my inability to understand why they don't look more at the bone marrow.

Best of luck