Is it necesary that a mastectomy or quadrantectomy be required after complete pathological response to breast cancer?

Yes and depends: We have never been able to prove that leaving breast cancer in place after chemo or hormone treatment alone with complete path response is safe. We could shrink to perform breast conserving surgery but at times mastectomy may be indicated. We look forward to a trial that is looking at radiation vs not in complete responders who present with more advanced breast cancer.

Yes. : The problem is you will not know it is a complete pathological response until the area is removed, proving that there was no microscopic cancer left. Theoretically, if we somehow knew it was a complete pathological response prior to surgery, then maybe it would not be necessary, but that is not possible at this time without surgery.