Abstract P1-04-12: Prognostic value of CTC detection by RT-PCR and the CellSearch system before first-line chemotherapy in metastatic breast cancer

Abstract

Abstract Background: CTCs have significant prognostic role in patients with breast cancer. Several techniques developed for CTC detection might help in monitoring treatment efficacy. The CellSearch System is the only clinically validated for use in patients with metastatic breast cancer (MBC). We have previously shown a concordance between RT-PCR for cytokeratin 19 (CK-19) and CellSearch System in the detection of CTCs in MBC. In this study we aimed to evaluate the prognostic value of CTC detection using these assays in the same cohort of patients. Methods: Blood was obtained from patients with MBC before the initiation of first-line chemotherapy. Different aliquots of the same blood sample were evaluated for the presence of CTCs by RT-PCR for CK-19 mRNA and by the CellSearch System. Disease progression and response to treatment were determined using standard clinical and imaging criteria. Results: In 142 patients with available clinical data, CTC evaluation was performed using both methods. Median age was 60.7 years (range, 23-82), 74.6% were post-menopausal and 16.9% were HER2-positive. CTCs were detected in 52.1% and 36.6% of patients by the CellSearch System (cut-offs ≥2 and ≥5 CTCs/7.5 ml, respectively) and in 38.7% by RT-PCR; 27.5% (cut-off ≥2) and 20.4% (cut-off ≥5) of patients were CTC-positive by both methods. Response rate was 40% in patients with CTCs detected by CellSearch (cut-off ≥2) vs 62% in CTC-negative patients; there was no difference in objective responses using the ≥5 cut-off, or using RT-PCR for CTC detection. Median PFS was 9.0 (cut-off ≥2) and 7.5 months (cut-off ≥5) for CTC-positive versus 20.0 (cut-off ≥2) and 18.7 months (cut-off ≥5) for CTC-negative patients using the CellSearch System (p = 0.0001). No significant difference in PFS was evident according to CTC detection by RT-PCR (10.0 vs 13.1 months, p = 0.253). Median survival was 24.7 vs 57.3 (cut-off ≥2) and 18.5 vs 53.7 (cut-off ≥5) months for CTC-positive vs CTC-negative patients using the CellSearch System (p = 0.0001); by RT-PCR, median survival was 30.3 and 50.1 months for CTC-positive and CTC-negative patients, respectively (p = 0.021). Conclusions: The detection of CTCs before first-line chemotherapy using either the CellSearch System or RT-PCR for CK-19 mRNA has significant prognostic value in patients with MBC. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-04-12.