Survival impact of adjuvant chemotherapy regimens for small (T1mi/a/b), node-negative (pN0), triple-negative breast cancer (TNBC)

Given the rarity of stage 1 triple negative breast cancer, we extracted recurrence & survival data from within the ASCO-developed CancerLinQ database to perform an in-depth retrospective analysis involving women with small (pT1mi/a/b), node-negative (pN0), TNBC who underwent curative breast surgery and were diagnosed between the years 2002-2023. For the adjuvant chemotherapy recipients, only those who received a regimen of either taxane chemotherapy plus cyclophosphamide (TC) or an anthracycline & cyclophosphamide combined followed by taxane chemotherapy (AC-T) were included in this study. Our co-primary objectives were to compare the invasive recurrence-free survival (iRFS) and overall survival (OS) of patients who received adjuvant TC or AC-T versus those receiving locoregional therapy alone. Our secondary outcome included an iRFS comparison between AC-T, TC, & locoregional therapy. Clinicopathologic variables were compared with appropriate tests for the categorical and continuous variables.

Among the 159 patients identified with T1mi/a/b N0 TNBC who met inclusion criteria, 42 had undergone locoregional therapy alone, 77 had received TC chemotherapy, and 40 received AC-T. Baseline demographics found that the locoregional group had a higher proportion of T1mi/a vs T1b patients (p < 0.001) & a higher average age (p < 0.002). No differences were seen between groups in terms of germline mutations (BRCA1, BRCA1, PALB2, CHEK2, & ATM), tumor grade, lymphovascular invasion, surgery type, race, ethnicity, or average body-mass index. After a median follow up period of 57.2 months overall, we found there was a significant benefit in both iRFS (HR 2.52, 95% CI 1.1-5.83, p = 0.025) & OS (HR 6.95, 95% CI 1.62-29.79, p = 0.0027) for those who received adjuvant chemotherapy (TC or AC-T) compared to locoregional therapy alone. The 5-year iRFS was 89.9% with AC-T, 77.1% with TC, & 69.1% with locoregional therapy, whereas the 5-year OS was 96.9%, 96.3%, 85.8%, respectively.

These findings suggest that a recurrence & survival benefit is seen with the application of adjuvant chemotherapy, even among this clinically low-risk population. However, whether it needs to be AC-T or TC appears less significant.