Preoperative Accelerated Partial Breast Irradiation in Patients With Locally Recurrent or Second Primary Breast Cancer

This study evaluates the acute toxicity and feasibility of repeat breast conserving therapy with preoperative accelerated partial breast re-irradiation (PAPBI) in female patients aged 51 years or older with ipsilateral recurrent or second primary low-risk breast cancer or DCIS.

Inclusion Criteria: * Female patients ≥ 51 years * Ipsilateral breast cancer; recurrence or second primary * Either histologically proven invasive adenocarcinoma (invasive adenocarcinoma with DCIS component is also accepted) or DCIS alone (calcification associated on imaging) * Histologically proven estrogen receptor positive * HER2neu negative * In case of invasive adenocarcinoma: tumor size ≤ 3 cm. In case of DCIS alone: affected area ≤ 2.5 cm * Grade I or grade II (biopsy) * cN0M0 (No evidence of nodal or distant metastases on axillary ultrasound and, if indicated, positron emission tomography-computed tomography (PET-CT) scan) * Unifocal lesions on mammogram and MRI (small satellite lesions adjacent to the tumor are accepted as long as it is suitable for local excision) * Interval since completion of local treatment of primary tumor \> 12 months * Previous radiotherapy (whole breast or partial) of the ipsilateral breast * Repeat breast conserving surgery feasible * World Health Organization (WHO) performance ≤ 2 * Written informed consent * The patient is legally competent Exclusion Criteria: * ≥ grade 3 radiotherapy toxicity in the breast after treatment of the primary tumor * Previous boost radiotherapy is not allowed, UNLESS the protocol tumor lies outside of the original boost area * Distant metastases and/or synchronous contralateral invasive or in situ carcinoma * Invasive lobular carcinoma (ILC) or pleiomorphic lobular carcinoma in situ (LCIS) * ER negative subtype * Lymphovascular invasion in biopsy * Neoadjuvant systemic treatment for the protocol tumor (except for pre-surgery hormonal therapy ≤ 2 months) * (Planned) oncoplastic surgery with major tissue displacement * Participation in another clinical trial that interferes with the locoregional treatment of this protocol. * It is expected that dosimetric constraints cannot be met, such as lung/heart constraints. * Patients with proven BRCA-mutations