Heterogeneity in Outcomes of Pathologic T1-2N1 Breast Cancer After Mastectomy: Looking Beyond Locoregional Failure Rates.

Purpose: A meta-analysis of 22 randomized trials accrued from 1964 to 1986 demonstrated significantly higher rates of locoregional failure (LRF) and breast-cancer mortality in women with 1-3 positive nodes without postmastectomy radiotherapy (PMRT) after mastectomy (mast.). Recent data demonstrate that PMRT reduces distant metastases (DM) in women with pN1 disease. The challenge today is whether all patients with pathologic T1-2pN1 disease have similar substantial LRF/DM risk that routinely warrants PMRT.

Methods: We reviewed patients with pT1-2N1 breast cancer treated with mast. ± adjuvant systemic therapy without PMRT from 2000 to 2013. The endpoints were LRF and DM rates, estimated by cumulative incidence method.

Results: We identified 468 patients with median follow-up of 6.3 years. Most (71%) were estrogen receptor/progesterone receptor + human epidermal growth factor receptor 2 (HER2). There were 269 patients with 1+ node, 140 patients with 2+ nodes, and 59 patients with 3+ nodes. The 6-year LRF/DM rates were 4.1%/8.4%. Patients with 1+, 2+, and 3+ nodes had 6-year LRF of 2.3, 5.1 and 8.9%, respectively (p = 0.13). The 6-year DM rate was higher in patients with 3+ nodes versus 1-2+ nodes: 15.7% versus 7.4% (p = 0.02). Several subgroups had low 6-year LRF and DM rates, including T1/1+ node (0.8%/4.1% LRF/DM) and micrometastases (0%/5.8% LRF/DM).

Conclusions: Patients with pT1-2pN1 represent a heterogeneous group with a wide range of LRF/DM rates. In particular, patients with pT1 tumors and 1 + LN, and patients with micrometastases, had low event rates. These groups would derive small absolute reductions in LRF and DM with addition of PMRT, underscoring the importance of patient selection for PMRT in pT1-2pN1 breast cancer.