2874 - A Multi-Institutional Pooled Analysis of Women with pT1-2N1 Breast Cancer after Mastectomy and Sentinel Lymph Node Biopsy Only and Adjuvant Post-Mastectomy Radiation
Presenter(s)
S. M. C. Sittenfeld1, E. Zabor2, S. N. Hamilton3, H. M. Kuerer4, M. El-Tamer5, G. E. Naoum6, A. Nichol7, B. D. Smith8, W. A. Woodward9, T. A. Moo10, S. N. Powell6, J. Kocsis11, A. G. Taghian12, I. Abu-Gheida13, and R. D. Tendulkar11; 1Department of Radiation Oncology, University of Cincinnati Cancer Center, Cincinnati, OH, 2Cleveland Clinic, Cleveland, OH, 3BC Cancer, Vancouver, BC, Canada, 4MDACC, Houston, TX, 5MSKCC, New York, NY, 6Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, 7BC Cancer - Vancouver, Vancouver, BC, Canada, 8Department of Breast Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 9MD Anderson Cancer Center, Houston, TX, 10Memorial Sloan Kettering Cancer center, New York, NY, 11Department of Radiation Oncology, Cleveland Clinic Foundation, Cleveland, OH, 12Harvard Medical School, Boston, MA, 13The University of Texas MD Anderson Cancer Center, Houston, TX
Purpose/Objective(s): To evaluate recurrence and mortality outcomes in women with pT1-2N1 breast cancer undergoing mastectomy + sentinel lymph node biopsy (SLNB) without axillary lymph node dissection (ALND), with adjuvant post-mastectomy radiation (PMRT), as recommended by 2025 ASCO guidelines.
Materials/Methods: Data from five North American institutions were pooled to include women who underwent mastectomy without neoadjuvant therapy, with pT1-2N1M0 disease from 1995-2015. Only patients undergoing SLNB who then received PMRT were included. Competing risks methods were used and cumulative incidence (CI) of locoregional recurrence (LRR) was estimated at 5- and 10-years.
Results: A total of 532 patients met criteria. Median age at diagnosis was 54 years, median tumor size was 2.3 cm, and 93% (n=493) had 1-2 positive lymph nodes (LN) with a median of 3 removed. Most tumors were ER+ or PR+ (90%), Her2- (85%), and 92% of patients received optimal systemic therapy (endocrine therapy if ER+, trastuzumab if Her2+, and chemotherapy if ER-). Typical radiation fields included chest wall + regional lymph nodes, most commonly to a dose of 50 Gy/25 fractions. At a median follow up of 4.9 years (IQR 3.6-6.4 years) there were only five LRRs, with 5- and 10-year CIs of LRR of 0.6% (95% CI 0.2-1.6%) and 1.7% (95% CI 0.5-4.1%). The 5- and 10- year CIs of any recurrence were 6.4% (95% CI 4.4-9%) and 9.1% (95% CI 6.2-13%), with larger tumor size, grade 3, lymphovascular invasion (LVI), and inner quadrant tumor location associated with increased hazard of any recurrence, whereas ER+ was associated with decreased hazard of any recurrence as compared to ER- (all p<0.05). There were 26 patients who died from breast cancer, with 5- and 10-year CIs of breast cancer mortality (BCM) of 4.5% (95% CI 2.8-6.8%) and 9.6% (95% CI 5.2-16%). Larger tumor size, grade 3, LVI, and inner quadrant tumor location were associated with increased hazard of BCM, whereas ER+ was associated with decreased hazard of BCM as compared to ER- (all p<0.05).
Conclusion: Adjuvant PMRT to the chest wall and regional nodes in patients with pT1-2N1 breast cancer after mastectomy and SLNB, in the absence of axillary dissection, is highly effective and associated with very low rates of locoregional recurrence, supporting the 2025 ASCO guideline recommendations.