Outcomes of Radiotherapy Boost in Breast Cancer Patients with Undissected Supraclavicular and/or Internal Mammary Lymph Node Metastasis

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<h3>Purpose/Objective(s)</h3> To evaluate the outcomes in breast cancer patients with clinically significant undissected supraclavicular (SCF) nodes and/or internal mammary lymph nodes (IMN) with or without nodal boost. <h3>Materials/Methods</h3> A retrospective study of 89 patients with clinically positive SCF and/or IMN metastasis treated with curative intent from January 2002 to December 2018 was done. Female breast cancer patients with no distant metastasis, previous history of any cancers, or any synchronous cancer were included. Clinically positive SCF and/or IMN metastasis was defined as radiological significant lymph node seen on imaging, including ultrasound and computed tomography scan, with or without biopsy confirmation. All patients received either neoadjuvant or adjuvant chemotherapy, and all patients underwent either mastectomy or breast conserving surgery, with axillary clearance. Post-operative RT to chest wall or whole breast and nodes included 50 Gy/25# or 40 Gy/15#, with or without a boost of 6-18 Gy. <h3>Results</h3> 89 patients were analyzed; 28 had IMN and 62 had SCF node involvement on diagnosis. 70 patients received neoadjuvant chemotherapy while 19 patients received adjuvant chemotherapy. 80 patients underwent mastectomy and 9 patients had breast conserving surgery. All patients received radiotherapy of which 40 patients had RT boost and 49 had no RT boost. After a median follow-up of 65 months, there were 30 (33.7%) deaths which were all breast cancer related. 32 patients had disease recurrence of which 14 patients had RT boost and 18 did not have RT boost. Of the 14 relapsed patients with RT boost, 7 (50%) patients had locoregional recurrence of which 3 (21%) were boost in-field recurrences. Of the 18 patients without RT boost with disease recurrence, 10 (56%) patients had locoregional recurrence. The 5-year overall survival (OS), disease free survival (DFS) and locoregional free survival (LRFS) rates of patients with RT boost compared to no RT boost were 57.9% vs 51.1% (p = 0.99), 42.1% vs 34.0% (p = 0.46) and 47.4% vs 38.3% (p = 0.66) respectively. Sub-group analysis of patients with SCF boost vs no SCF boost showed a 5-year OS, DFS and LRFS of 56.7% vs 48.3% (p = 0.70), 40% vs 31% (p = 0.64) and 43.3% vs 34.5% (p=0.52) respectively, while patients with IMN boost vs no IMN boost had a 5-year OS, DFS and LRFS of 62.5% vs 52.6% (p = 0.71), 50.0% vs 36.8% (p = 0.95) and 62.5% vs 42.1% (p = 0.33) respectively. <h3>Conclusion</h3> In patients with undissected SCF and/or IMN metastasis, there was a high rate of breast cancer related death. Of 40 patients who received RT boost, only 3 experienced in-field recurrence. We demonstrated a signal of better locoregional control for RT boost in clinically significant IMN or SCF nodes in breast cancer patients, although no statistical significance is achieved likely due to low rates of locoregional recurrences. Further study with a larger cohort is warranted.