you may find this publication interesting 

http://www.ncbi.nlm.nih.gov/pubmed/14673041

it is a retrospective study that indicates that In patients achieving a clinical complete response to neoadjuvant chemotherapy, radiotherapy alone achieved survival rates as good as with surgery, but with higher local recurrence rates.

A provocative question. Zardavas D nicely provided a good research attached above which was published in 2003 by the Royal Marsden Hospital. More than 10 years have lapsed but oncologists now still don't know when and by what criteria, "NOT" to submit patients for surgical resection particularly total mastectomy + axillary lymph node dissection (ALND) after a successful neoadjuvant chemotherapy. Theoretically, with a pCR (ypTis or ypT0 + ypN0) rate, let say, of 30%, probably, at least a quarter of women may safely avoid mastectomy + ALND. If "radical" radiotherapy is added for amenable residual tumors, much greater proportion of women can skip the mastectomy to continue adjuvant systemic treatment. So far, the above statements should require clinical trials to prove.

the problem is that for pWhatever response we need excision of the tumor.... the point is, in which cases can we avoide excision?

I was thinking on designing a trial starting on mice, do not know if viable...

Probably using the criteria of complete response by post-neoadjuvant ultrasound or post-neoadjuvant PET-CT scan.

and what if we go rt before surgery? I mean think on rectal cancer and complete pathologic response after neoadjuvant treatment. Are there any cases we could avoid surgery?Or do CDis low grade, limited disease need surgery? Can we just Tamoxifene and wait and see?

Indeed hard question but it is an open window!

I think, A study is already in progress; tumour localizer before chemotherapy. post chemotherapy biopsy of tumour bed (guidance by localizer). If Biopsy negative radiation and follow up. If Biopsy positive of course surgery is mandatory.

I personally used this approach since 1993.Some patients with complete clinical response following primary chemotherapy for breast cancer refuse surgery.The microscopic rest might cause local recurrence only if it is radioresistant.I treated nearly 25 cases like that.Only a few of them recurred during long term follow up.And no one of them developed metastasis.I eagerly advice this approach to suitable and cooperating patients...

There is no need to know whether CTC+ or not in cases with clinically complet result after primary chemoterapy...Can surgery relieve CTC positivity ?No..

Without pathologic staging ,may only cause to underestimate the prognosis .

Despite these,prognosis will not be worse.Only disease-free survival may be decreased..

The study of reliability of Biopsy post NACT is out. Clinical Complete resposnse include radiologically no evidence of tumour. These patients were biopsied in tumour bed, guided by tumour marker placed when tumour was palpable!

It turn out that such biopsies are unreliable to detect possible viable tumour!

So for Now, one cannot avoid surgery post NACT, even if there is clinical complete response! Surgery remains most important tool for cure of breast cancer.