IMPORTANCE: Current practices in axillary treatment for patients with breast cancer who receive a mastectomy for node-positive disease are unknown. For patients who receive postmastectomy radiotherapy (PMRT), the addition of axillary lymph node dissection (ALND) may result in significant overtreatment. OBJECTIVES: To evaluate trends in axillary treatment for patients with limited nodal metastases who receive a mastectomy and identify factors that can be targeted to reduce axillary overtreatment. DESIGN, SETTING, AND PARTICIPANTS: A retrospective cohort study was conducted of patients identified from the National Cancer Database who received a diagnosis of breast cancer from January 1, 2012, to December 31, 2021. Patients included were women aged 18 years or older with clinical (c) T1-T2N0 breast cancer who underwent mastectomy with axillary staging with sentinel lymph node biopsy (SLNB) and/or ALND and had 1 to 2 positive lymph nodes. Patients who received neoadjuvant therapies were excluded. Statistical analysis was performed from December 2023 to July 2024. EXPOSURE: Axillary management based on ALND and PMRT receipt: (1) ALND alone, (2) PMRT alone, (3) both ALND and PMRT, and (4) neither ALND nor PMRT. MAIN OUTCOMES AND MEASURES: Axillary management strategies were evaluated, and clinicopathologic characteristics based on treatment type were compared with multivariable analysis. RESULTS: In total, 62 332 patients were included (median age, 58 years [IQR, 48-68 years]
82.2% with Charlson-Deyo comorbidity score 0). The proportion of patients who received ALND alone decreased from 47.1% to 17.6% from 2012 to 2021, while the percentage of patients who received PMRT alone increased from 9.8% to 36.8%. Overall, 21.3% of patients received treatment with both ALND and PMRT, with little change over time (from 21.7% in 2012 to 17.7% in 2021). Most patients (88.4%) who received both PMRT and ALND underwent ALND at the same operation as SLNB. Younger age (odds ratio [OR] per year increase, 0.98 [95% CI, 0.98-0.98]
P <
.001), high-grade tumors (grade 2: OR, 1.18 [95% CI, 1.09-1.29]
P <
.001
grade 3: OR, 1.34 [95% CI, 1.22-1.48]
P <
.001), presence of lymphovascular invasion (OR, 1.26 [1.19-1.33]
P <
.001), and larger tumor size (cT2 tumors compared with cT1: OR, 1.10 [95% CI, 1.03-1.17]
P = .004
upstaging to pathologic T3 tumors: OR, 2.29 [95% CI, 1.15-4.99]
P = .03) were associated with increased likelihood of concurrent treatment with ALND and PMRT. CONCLUSIONS AND RELEVANCE: In this retrospective cohort study of patients with breast cancer who received a mastectomy, a substantial proportion of those with 1 to 2 positive lymph nodes were treated with both ALND and PMRT. Delaying the decision for ALND until after multidisciplinary input may reduce overtreatment.