Circulating tumor cells in immunohistochemical subtypes of metastatic breast cancer: lack of prediction in HER2-positive disease treated with targeted therapy.

BACKGROUND Circulating tumor cells (CTCs) are associated with inferior prognosis in metastatic breast cancer (MBC). We hypothesized that the relationship between CTCs and disease subtype would provide a better understanding of the clinical and biologic behavior of MBC. PATIENTS AND METHODS We retrospectively analyzed 517 MBC patients treated at a single institution. Subtypes of primary tumors were analyzed by immunohistochemical (IHC) or fluorescent in situ hybridization analyses and CTCs were enumerated by CellSearch(®) at starting a new therapy. Overall survival (OS) and progression-free survival durations for each IHC subtype were determined. RESULTS At a median follow-up of 24.6 months, 276 of 517 (53%) patients had died. The median OS for patients with <5 and ≥ 5 CTCs were 32.4 and 18.3 months, respectively (P < 0.001). Except in HER2+ patients, the prognostic value of CTCs was independent of disease subtype and disease site. CONCLUSIONS In this large retrospective study, CTCs were strongly predictive of survival in all MBC subtypes except HER2+ patients who had been treated with targeted therapy. Our results clearly demonstrate the value of enumerating CTCs in MBC and strongly suggest an interesting biological implication in the HER2+ subset of patients that need to be further explored.