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Abstract Background An important component of the RAS signalling pathway, the RAS p21 oncogene, is frequently hyperactivated in breast cancer. Its expression in tumor tissue has been linked to poor clinical outcome. This study was designed to evaluate the clinical relevance of RAS p21 levels in peripheral blood in a large cohort of metastatic breast cancer patients. Methods Two hundred fifty-one patients with metastatic breast cancer were enrolled in this prospective, multicentre, open-label, non-randomized study. Blood samples were collected before start of first-line or later-line treatment. RAS p21 was determined using a sandwich-type ELISA immunoassay. For the determination of the cutoff, blood samples from age-matched healthy controls were analyzed. A value above 452 pg/ml was regarded as elevated (mean + 2 x SD). In the univariate survival analysis, two other cutoffs were considered as well (50th and 75th percentile of patients, i.e. 229 pg/ml and 320 pg/ml). Circulating tumor cells (CTCs) were detected using the CellSearch system. Results 29 of 251 (12%) patients had RAS p21 levels above the cut-off level of 452 pg/ml. Clinical-pathological parameters, such as hormone receptor and HER2 status, line of therapy and CTC status, did not correlate with RAS p21 levels. Elevated RAS p21 was significantly associated with shorter progression-free and overall survival in the univariate analysis (median PFS: 3.9 months [95%-CI: 1.8–6.0] for patients with elevated RAS p21 levels versus 8.5 months [95%-CI: 7.4–9.5] with non-elevated levels [p = 0.01]; median OS: 7.1 months [95%-CI: 0.3–14.2] versus not reached [p = 0.002], respectively). When RAS p21 cutoffs other than 452 pg/ml were considered, elevated RAS p21 was significantly associated with OS but not with PFS. Classical clinical-pathological factors were included into a multivariate Cox regression analysis. In addition, factors previously shown to influence survival in a univariate analysis, such as serum HER2, CAIX and TIMP1, were included as well. In the multivariate analysis, RAS p21, presence of ≥5 CTCs per 7.5 ml blood, higher grading and higher line of therapy remained independent predictors of shorter OS. Conclusions Metastatic breast cancer patients with elevated levels of circulating RAS p21 have significantly worse clinical outcome. Hypothetically, these patients might benefit from therapeutic strategies targeting RAS pathway. Trial registration Current Controlled Trials ISRCTN59722891 (DETECT); trial registration date: April, 17th 2010; the trial was registered retrospectively.

Circulating tumor cells (CTCs) have gained importance as an emerging biomarker in solid tumors in the last two decades. Several detection assays have been introduced by various study groups, with EpCAM-based CellSearch system being the most widely used and standardized technique. In breast cancer, detection of CTCs correlates with clinical outcome in early and metastatic settings. CTC persistence beyond first cycle of palliative chemotherapy indicates poor response to treatment in metastatic situation. Beyond prognostication and therapy monitoring, CTC counts can guide treatment decisions in hormone receptor positive HER2-negative metastatic breast cancer. Furthermore, CTC-based therapy interventions are currently under investigation in clinical trials. In this review, we focus on the current state of knowledge and possible clinical applications of CTC diagnostics in patients with metastatic breast cancer.

The phenomenon of hematogenous tumor cell dissemination in patients with solid tumors has been extensively explored over the last decades. Breast cancer research investigated at first disseminated tumor cells (DTCs) in the bone marrow; however, the focus soon moved to circulating tumor cells (CTCs) in the peripheral blood as blood is easily accessible without an invasive procedure. The prognostic significance of CTC presence has been shown in large studies both in adjuvant and metastatic setting and commercially available detection assays have been evaluated for monitoring in clinical trials. Beyond detection and enumeration of CTCs, the characterization of single tumor cells may enhance our knowledge on disease progression and thus optimize treatment choices.