Outcomes by molecular subtype after accelerated partial breast irradiation using single-entry catheters

Tumor biology is being recognized as an important indicator of prognosis and risk of locoregional recurrence. Here, we determine actuarial recurrence rates by approximated molecular subtype for women treated with single-entry catheter accelerated partial breast irradiation (sAPBI).

One thousand four hundred eighty-six women with invasive cancer having known ER, PR, and Her2 status and at least 1-year of followup were treated using MammoSite, Contura, or SAVI sAPBI from 2002 to 2014 at our institution. Actuarial recurrence rates were determined for the following four approximated molecular subtypes using the Kaplan-Meier method: luminal A (n = 1081), luminal B (n = 164), Her2 (n = 123), and triple-negative breast cancer (TNBC; n = 118).

With a median followup time of 3.3 years (range 1-13.6 years), the 5-year in-breast tumor recurrence rate was 2.6% overall, 2.1% for luminal A, 1.5% for luminal B, 4.9% for Her2, and 5.4% for TNBC. Luminal A and B subtypes, as compared with the more aggressive Her2 and TNBC subtypes combined, demonstrated lower 5-year in-breast tumor recurrence (2.1% vs. 5.1%, p = 0.021). The 5-year regional nodal recurrence rate was 1.4% overall, 1.4% for luminal A, 0% for luminal B, 1% for Her2, and 4.2% for TNBC. The 5-year locoregional control is 97.3% for luminal breast cancers and 93.8% for the more aggressive Her2 and TNBC subtypes collectively.

Luminal cancers demonstrated excellent 5-year locoregional control with sAPBI. Although caution should be used when treating patients with the more aggressive Her2 and TNBC subtypes, these subtypes have demonstrated higher LRR with mastectomy and whole-breast irradiation. Further randomized comparisons are needed to determine the optimal treatment for these higher risk patients.