Prognostic value of HER2 status on circulating tumor cells in advanced-stage breast cancer patients with HER2-negative tumors

Discordance between HER2 expression in tumor tissue (tHER2) and HER2 status on circulating tumor cells (cHER2) has been reported. It remains largely underexplored whether patients with tHER2−/cHER2+ can benefit from anti-HER2 targeted therapies. cHER2 status was determined in 105 advanced-stage patients with tHER2− breast tumors. Association between cHER2 status and progression-free survival (PFS) was analyzed by univariate and multivariate Cox models and survival differences were compared by Kaplan–Meier method. Compared to the patients with low-risk cHER2 (cHER2+ < 2), those with high-risk cHER2 (cHER2+ ≥ 2) had shorter survival time and an increased risk for disease progression (hazard ratio [HR] 2.16, 95% confidence interval [CI] 1.20–3.88, P = 0.010). Among the patients with high-risk cHER2, those who received anti-HER2 targeted therapies had improved PFS compared with those who did not (HR 0.30, 95% CI 0.10–0.92, P = 0.035). In comparison, anti-HER2 targeted therapy did not affect PFS among those with low-risk cHER2 (HR 0.70, 95% CI 0.36–1.38, P = 0.306). Similar results were obtained after adjusting covariates. A longitudinal analysis of 67 patients with cHER2 detected during follow-ups found that those whose cHER2 status changed from high-risk at baseline to low-risk at first follow-up exhibited a significantly improved survival compared to those whose cHER2 remained high-risk (median PFS: 11.7 weeks vs. 2.0 weeks, log-rank P = 0.001). In advanced-stage breast cancer patients with tHER2− tumors, cHER2 status has the potential to guide the use of anti-HER2 targeted therapy in patients with high-risk cHER2.