Association between insulin-like growth factor-1 receptor (IGF1R) expression in circulating tumor cells (CTCs) and prognosis in patients with metastatic breast cancer (MBC).

Abstract

1086 Background: CTCs are strongly associated with prognosis in MBC. In a recent metanalysis on 1944 patients, a CTC count > 5/7.5 ml was associated with a 2-fold increased risk of progression and death. Little evidence is available on the prognostic role of phenotypic CTC assessment, however. In this study, nested in a randomized clinical trial of Ist line chemotherapy ± metformin, we evaluated the prognostic role of IGF1R expression in CTCs, given its potential growth promoting effect. Methods: CTCs were isolated from blood samples of enrolled patients; an automated sample preparation and analysis system (CellSearch) was customized for detecting IGF1R positive CTCs. The prognostic role of total CTCs, IGF1R positive (+ve) and negative (-ve) CTCs was assessed by fitting different PFS and OS multivariate Cox’s models.Results: CTC evaluation at baseline was performed in 72 of 126 patients, of whom 30 (42%) had CTCs ≥5/7,5ml and 41 (57%) had at least one IGF1R+ve CTC. In univariate analysis the prognostic role of total CTCs was confirmed: PFS ( < 5 vs ≥5) HR = 1.69, 95%CI 1.01-2.69, p 0.042 and OS HR = 2.80, 95%CI 1.47-5.30, p 0.002).However, when total CTCs were split in IGF1R+ve and IGF1R–ve, a striking difference was seen in the prognostic effect of these cell types.While no association was detected between an increasing number of IGF1R+ve CTCs and PFS or OS (p = 0.56 and p = 0.99), the number of IGF1R-ve CTCs ( < 4 vs ≥4) was strongly associated with an increased risk of progression and death: HR 1.93 (95%CI 1.15-3.23, p 0.013) and 3.65 (95%CI 1.88-7.09, p 0.001). In multivariate analysis, adjusted for metformin, the prognostic role of the number of IGF1R-ve CTCs was confirmed, while no residual prognostic role of total CTCs or number of IGF1R+ve cells was found (p = 0.55 and p = 0.64 for PFS; p = 0.86 in both cases for OS). Conclusions: In our study, the loss of IGF1R expression in CTCs exhibited a significant adverse prognostic effect, whereas no significant effect of total CTCs and IGF1R+ve CTCs was observed. This finding supports the biological characterization of CTCs as a critical step for further definition of their prognostic significance.