• Pauline T Truong, Mary Lesperance, Aydin Culhaci, Hosam A Kader, Caroline H Speers, and Ivo A Olivotto.
• Radiation Therapy Program, British Columbia Cancer Agency, Vancouver Island Centre, University of British Columbia, Victoria, BC, Canada. ptruong@bccancer.bc.ca
• Int. J. Radiat. Oncol. Biol. Phys. 2005 May 1; 62 (1): 175-82.

PurposeTo identify patient subsets with T1-T2N0 breast cancer at high risk of locoregional recurrence (LRR) who may warrant consideration for postmastectomy radiotherapy.Methods And MaterialsData were analyzed for 1505 women referred between 1989 and 1999 with pathologic T1-T2N0M0 breast cancer treated with mastectomy with clear margins and no adjuvant radiotherapy. Logistic regression analysis was performed to identify statistically significant factors associated with LRR. Recursive partitioning was used to develop a classification tree model for LRR given the prognostic variables.ResultsThe median follow-up was 7.0 years. The 10-year Kaplan-Meier LRR rate was 7.8%. On logistic regression analysis, the statistically significant factors predicting LRR were histologic grade (p <0.0001), lymphovascular invasion (LVI) (p <0.0001), T stage (p = 0.05), and systemic therapy use (p = 0.01). In the recursive partitioning model, the first split in the classification tree was histologic grade. For 972 patients without high-grade histologic features, the 10-year Kaplan-Meier LRR rate was 5.5%. For 533 patients with Grade 3 disease (LRR rate 12.1%), the concomitant presence of LVI was associated with a LRR rate of 21.2% (n = 126). In patients with Grade 3 disease without LVI, T2 tumors conferred a LRR rate of 13.4% (n = 194), which increased to 23.2% for patients who did not receive systemic therapy (n = 63).ConclusionWomen with pT1-T2N0 breast cancer experienced a LRR risk of approximately 20% in the presence of Grade 3 disease with LVI or Grade 3 disease, T2 tumors, and no systemic therapy. These subsets of node-negative patients warrant consideration of for postmastectomy radiotherapy.

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