The main purpose of the study is to evaluate the potential of a minimal invasive, vacuum-assisted biopsy (VAB) to reliably diagnose a pathological complete response (pCR) in the breast after neoadjuvant chemotherapy (NACT) in breast cancer patients.

The study is designed as a multicenter, confirmative, one-armed, intra-individually-controlled, open, diagnostic trial, in which we aim to confirm the applicability of preoperative VAB in patients after NACT. Furthermore, we aspire to quantify the rate of concordant pathological findings (pCR yes / no) in biopsy and surgical specimen.

In clinical routine surgical treatment follows the pre-operative chemotherapy (NACT). However, recent studies have demonstrated that shrinking tumors need less surgical treatment indicating that patients with pCR could potentially be spared of surgery in the future. However, up to now, prediction of pCR after NACT is only moderately accurate. This prospective, monocenter diagnostic trial aims to explore if minimal invasive biopsies (MIB) might overcome this diagnostic challenge.

Ultrasound guided VAB will be performed on 600 breast cancer patients after NACT and directly prior to surgery.

There are only two trial visits that are specific to the trial. All other visits will be routine visits.

1. The first trial visit will take place in order to provide the patient with detailed information on the study, its' aims, the VAB procedure, and its risks. The patient will be asked to sign a form of informed consent.

2. At the second trial visit the performance of the VAB (=index test) will take place. This trial visit may vary by patient, tumor, and trial site characteristics and may either be:

   1. An ultrasound guided VAB or
   2. A stereotactically / mammographically guided VAB. All possible VAB procedures and settings (in outpatient clinic, or in operating room directly before the surgery) are equally accepted. We will allow every trial site to choose the adequate setting to the trial site´s and to their patients' needs.

A visit for a follow up will not be necessary in this setting. Possible complications of the VAB procedure may occur while the biopsy is taken.

The pathological results of the VAB specimen will be generally categorized as follows:

1. Residual tumor cells in VAB specimen (=non-pCR)
2. No residual tumor cells in the VAB specimen and VAB representative of former tumor region (="pCR in VAB")
3. No residual tumor cells in the VAB specimen but VAB unclear or not representative of former tumor region (=possible sampling error). These VABs are categorized as uninformative for the primary endpoint of the clinical trial.

The results will be compared to those of the pathological examination of surgical specimen.

Inclusion Criteria

• Female patients with primary breast cancer after Neoadjuvant Chemotherapy (NACT) treatment which has been performed for at least 12 weeks and resulted in cPR or cCR (see below).
• >/=18 years
• any cT and cN stage, except cT4 stages
• any routine breast cancer surgical intervention planned according to guidelines (breast conservation or mastectomy)
• Residual intramammary target lesion or clip marker is visible in ultrasound and / or mammography
• Diagnosis of imaging complete or partial response according to RECIST 1.1 by at least mammography or ultrasound, according to local routine)
• Inclusion of only one breast per patient, in bilateral cancer one breast can be included
• In case of multicentric disease: confirmation of the same tumorbiological subtype defined by immunohistology in at least 2 lesions.
• Ability of subject to understand character and individual consequences of the clinical trial.
• Written informed consent (must be available before enrolment in the trial).

Exclusion Criteria

• Palliative or recurrent breast cancer
• in case of clip marker = target lesion: dislocation of marker (>5mm distance to the initial lesion border at the time of clip placement)
• contraindication for VAB or associated procedures (e.g. local anesthesia)
• Pregnancy and lactation
• held in an institution by legal or official order
• legally incapacitated.