Predictive Value of Circulating Tumor Cells (CTCs) in Metastatic Breast Cancer Patients Treated by Bevacizumab-Based Therapy

Background:Circulating tumor cells (CTC) are involved in cancer dissemination and are an independent prognostic factor in metastatic breast cancer (MBC). Antiangiogenic, bevacizumab-based chemotherapy improves response rate and progression free survival in patients with metastatic breast cancer (MBC), without impact on overall survival. Preclinical data suggest the possibility of increased metastatic potential of tumor cells pretreated by anti-angiogenic therapy (Ebos et al. Cancer Cell 2009,15: 232–9). The aim of this study was to determine the prognostic value of CTC in MBC patients treated by bevacizumab-based therapy.Patients and Methods: This retrospective study included 48 MBC treated with bevacizumab combined chemotherapy regimens and 46 patients treated with chemotherapy alone between January 2004 and December 2008 at M.D.Anderson Cancer Center. CTCs were detected and enumerated before patients started therapy using the CellSearch™ system (Veridex, LLC, NJ, USA). Progression free survival (PFS) and overall survival (OS) were calculated from the date of CTC measurement, estimated by the Kaplan-Meier product limit method, and compared between groups with the log-rank test.Results: At a median follow up of 10.1 months (range: 1-26 months), 22 patients (45.8%) had died. The estimated medians of PFS in bevacizumab-treated patients were 8.1 vs. 5.2 months (p = 0.42) in patients with baseline < 5 CTCs vs. ≥ 5 CTCs. Moreover, the OS for the two subgroups were 18.3 vs. 12.4 months (p = 0.41), respectively. Twenty-three patients had CTC measurements at the time of progression. Median CTC counts at baseline and at time of disease progression were 6 (range: 0-230) and 7 (range: 0-359) respectively in the bevacizumab-treated group. The median CTC counts in the control group at same time points were 7 (range: 0-724) and 2 (range:0-999), respectively. Thirteen (56.5%) and 12 (52.2%) patients had CTC ≥ 5 at baseline and at time of disease progression in bevacizumab-treated group compared to CTC counts of 24 (52.2%) and 17 (37%) in control group treated with chemotherapy without bevacizumab. Post progression overall survival in patients with CTC < 5 and CTC ≥ 5 measured at time of disease progression were 11.0 and 10.4 months (p = 0.36), in the bevacizumab treated group vs. 27 and 12.4 months (p = 0.04), in the control group respectively.Conclusion: Our data support the prognostic value of CTC measured before therapy in MBC. The detection of higher CTC counts at time of disease progression and the limited prognostic value of CTC after failure of bevacizumab-based chemotherapy although intriguing, warrants further prospective investigations. Moreover, a comparison between the differential effects of monoclonal antibodies and tyrosine kinases inhibitors on CTCs detection and monitoring will better clarify the role of specific targeted therapies on micrometastatic disease.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 3013.

Characterization of Metastatic Breast Cancer Patients with Non-Detectable Circulating Tumor Cells

Background: Circulating tumor cells (CTC) are independent predictor of progression free and overall survival in metastatic breast cancer patients, with superior prognosis for patients with CTC <5 per 7.5mL of peripheral blood. However, 30-50% of patients have non-detectable CTC. The aim of this study was to assess the prognostic factors in MBC patients with non-detectable CTC.Methods: This retrospective study included 271 MBC patients evaluated between January 2004 and December 2007. Median age of patients was 56 years (range: 23-82 years). CTCs were enumerated before patients started a new line of treatment using the CellSearchTM. Overall survival (OS) was calculated from the date of CTC measurement, estimated by the Kaplan-Meier product limit method, and compared between groups with the log-rank test.Results: Median CTC count was 2 (range: 0-1780) per 7.5 mL. CTCs were not detected in 99 (36.5%) patients, while 112 (41.3%) patients had CTC ≥ 5. Median OS for patients with 0 CTC; 1-4 CTC and ≥ 5 CTC was 29.3; 26.4; and 19.4 months (p = 0.04), respectively. Patients with brain metastasis have the highest probability of non-detectable CTC (71.4% vs. 33.6%; p = 0.001), while patients with bone metastasis are more likely to have CTC ≥ 1 (48.2% vs. 31.8%; p = 0.01). There was no association between other tumor characteristics (ER, PR, HER2, number and localization of tumor metastasis) and non-detectable CTC status. Patients with CTC = 0 have non-significantly better OS compared to patients with CTC ≥ 1 (29.3 vs. 23.3 months; p = 0.09) and have superior survival in all but one analyzed subgroups; only inflammatory breast cancer (IBC) patients with CTC = 0 have inferior OS compared with patients with CTC ≥ 1 (26 vs. 37 months; p = 0.67). In a subgroup of patients with non-detectable CTC, triple negative MBC has the poorest survival (median OS = 18.8 months), while hormone receptor positive MBC, without visceral metastases and non-inflammatory breast cancer has the best survival (median OS = 36.9 months). In multivariate analysis, hormone receptor status and line of therapy were only independent prognostic factors for OS in patients with non-detectable CTC (Table 1).Conclusion: Patients with non-detectable CTC before start of new line of therapy comprise a heterogeneous group of patients with substantially different prognosis. Triple negative and IBC patients represent poor prognosis subgroups. These data suggest heterogeneity of microscopic disease in advanced cancer and indicate the need to investigate combining additional detection technologies.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 3006.