Implications of HER2 amplification in small, node-negative breast cancers: do Asians differ?

BACKGROUND: We investigated the implications of HER2 amplification in Asian women with small, node-negative breast cancer in low- and middle-income countries (LMCs).
METHODS: We reviewed the charts patients treated between 1989 and 2009 with breast conservation therapy for node-negative breast cancers measuring ≤ 2 cm. Disease-free survival (DFS), ipsilateral breast tumor recurrence (IBTR), distant disease-free survival (DDFS), and overall survival (OS) rates were estimated using the Kaplan-Meier method and were compared by the log-rank test. Potential covariates-age, tumor grade, hormone receptor status--were analyzed by multivariate analysis.
RESULTS: A total of 519 patients were studied including 204 (39%) and 315 (61%) patients diagnosed with pT1ab and pT1c tumors, respectively. Median follow-up was 57 months. HER2 amplification was found in 17.1% of all patients and in 16.7% patients with pT1ab tumors. Among patients with T1ab tumors, 73.0 and 9.3% underwent adjuvant hormonal and chemotherapy, respectively; 3 of 34 T1ab patients with HER2-amplified tumors received trastuzumab. HER2 amplification was associated with poorer 5-year DFS (83.7% vs. 95.5%, P < 0.0001), DDFS (87.5% vs. 97.9%, P < 0.0001), and IBTR (8.6% vs. 2.1%, P < 0.0001) rates in patients with pT1 tumors. Multivariate analysis showed that HER2 amplification remained a significant negative prognostic factor for DFS [hazard ratio (HR) 4.1, 95% confidence interval (CI) 2.1-7.8, P < 0.0001], DDFS (HR 6.3, 95% CI 2.4-17.0, P < 0.0001), and IBTR (HR 4.5, 95% CI 2.0-10.0, P < 0.0001) rates. In the pT1ab subgroup, univariate analysis showed that HER2 amplification prognosticated for DFS (85.1% vs. 95.7%, P = 0.022) and IBTR (14.9% vs. 3.5%, P = 0.004) rates but not for the OS (100% vs. 99.2%, P = 0.487) rate. Similar results were obtained after excluding patients given trastuzumab.
CONCLUSIONS: The decision to use trastuzumab in HER2-amplified pT1ab tumors must balance their poor outcome against intrinsic financial limitations in LMCs. Patient selection criteria needs fine-tuning, and resource-sensitive regimens must be explored.