Favorable Locoregional Control in Clinically Node- Negative Hormone-receptor Positive Breast Cancer With Low 21-gene Recurrence Scores: a Single Institutional Study With 10-year Follow-up

Abstract Background: Recent studies have shown a lower likelihood of locoregional recurrences in patients with low 21-gene recurrence score (RS). In this single institutional study, we investigated any associations between different cut-off values of 21-gene RS and histopathological factors and outcome in patients with long-term follow-up. Methods: Between February 2010 to February 2013, 61 patients with early stage clinically node-negative hormone receptor-positive and HER2-negative breast cancer tested for the 21-gene RS assay, were included into the study. Demographic, clinicopathological, treatment and outcome characteristics were analyzed.Results: Median age was 48 (range, 29-72). Of those, 53 patients were diagnosed with Stage 1 (86.9%) and 8 patients were Stage 2 (13.1%) following surgery. Patients with high histologic grade (HG), or with Ki-67>25%were more likely to have intermediate/high RS based on RS >11 and >18. Based on the 21-gene RS assay, only 19 patients (31%) received adjuvant chemotherapy. At a median follow-up of 112 months, 3 patients developed local recurrences (4.9%) treated with endocrine therapy alone. Among patients treated with endocrine treatment alone (n=42), the clinicopathological characteristics including age <40, age <50, high histologic or nuclear grade, high Ki67-scores (>20%, >25%, >30%), presence of lymphovascular invasion, luminal-A type, multifocality, lymph node positivity, tumor size more than 2 cm, RS>18 or RS>11 were not significantly found to be associated with 10-year locoregional recurrence free survival (LRRFS). However, patients with a RS >16 have significantly shown a poorer 10-year LRRFS compared to those with RS <16 (RS <16; 100% vs RS>16; 75%, p=0.039). Conclusions: These results suggest that Oncotpe DX assay may be of little value in patients with high histologic grade or high Ki67 scores (>25%) as treatment decision criteria to determine any benefit from chemotherapy. Furthermore, patients with a RS >16 are more likely to benefit from adjuvant chemotherapies, whereas those with a RS <16 have an excellent outcome and local control on long term follow-up with endocrine treatment alone.