Omission of SLNB in Triple-negative and HER2-positive Breast Cancer Patients with RCR and PCR in the Breast After NAST

Inclusion Criteria:

• Written informed consent prior to breast-conserving surgery, including expectedcooperation of the patients for follow-up, must be obtained and documented accordingto the European regulatory requirements

• Histologically confirmed unilateral primary invasive carcinoma of the breast (corebiopsy). Multifocal or multicentric tumors are allowed if breast-conserving surgeryis planned.

• Age at diagnosis at least 18 years

• imaging techniques with estimated tumor stage between cT1-T3 prior to NAST

• triple-negative or HER2-positive invasive breast cancer

• clinically and sonographically tumor-free axilla prior to core biopsy (cN0/iN0)

• in cases with cN0 and iN+, a negative core biopsy or fine needle aspiration (FNA)biopsy of the sonographically suspected lymph node is required

• no evidence for distant metastasis (M0)

• standard NAST with radiologic complete response (rCR)

• planned breast-conserving surgery with postoperative external whole-breastirradiation (conventional fractionation or hypofractionation)

Exclusion Criteria:

• History of malignancy within last 5 years, except curatively treated basalioma ofthe skin and carcinoma in situ of the cervix

• Time since last cycle of NAST >3 months (optimal <1 month)

• histologically non-invasive breast carcinoma before NAST

• ER-positive (>=10% positive cells on IHC)/HER2-negative disease (triple-positivetumors are allowed)

• cT4 or iT4 tumors

• pregnant or lactating patients

• no radiologic complete response at the end of NAST

• planned total mastectomy after NAST

• planned intraoperative radiotherapy (e.g. Intrabeam) or postoperative partial breastirradiation (e.g. multicatheter technique) alone; both procedures are allowed asboost techniques

• male patients