In the case of primary surgery, in patients with sentinel node involvement, it has already been shown that omitting axillary lymph node dissection (ALND), often combining axillary radiotherapy (RT), does not worsen the prognosis and does significantly reduce the appearance of lymphedema. However, patients who have received neoadjuvant systemic treatment cannot benefit from this option, even though in the majority of those who have responded well to treatment, a residual disease in the armpit is low, but there are no studies yet published that supports the possibility of not performing lymphadenectomy.

The primary endpoint is to evaluate wether axillary radiotherapy (ART) presents a lower risk of lymphedema with respect to lymphadenectomy (ALND) in patients with breast cancer who, after neoadjuvant systemic treatment (NST), present the sentinel node affected. Likewise, we will evaluate recurrences and overall survival in both groups. Finally, we will analyze the quality of life of these patients.

A prospective, randomized, open-label, parallel-assigned, multicenter study. The estimated sample size is 820 patients (410 patients in neoadjuvant chemotherapy and 410 in neoadjuvant hormone therapy), over 5 years. Patients will be stratified and analyzed independently according to the neoadjuvant treatment regimen, whether chemotherapy (CT) +/- hormonal therapy (HT).

A pilot phase of the study was carried out with the first 200 patients (Until 1 May 2023), and an interim analysis will also be performed with these first 200 patients.

Inclusion Criteria:

• T1-T4 N0/ T0-T4 N1 at diagnosis and subsidiary of neoadjuvant treatment
• Post-CT SLN with ≤2 macrometastasis/micrometastasis or ITCs
• Post-CT axillary response by ultrasound or MRI
• Complete at least 70% of neoadjuvant chemotherapy and 6 months of endocrine treatment.

Exclusion Criteria:

• cN2
• ypN0
• History of breast surgery for ipsilateral cancer in the last 10 years
• History of other cancer in the last 5 years, except squamous carcinoma of the skin.