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Pre-treatment Circulating Tumor Cell Levels Correlate with Regional and Distant Failure Rates Following Stereotactic Body Radiation Therapy for Early Stage Non-small Cell Lung Cancer

Presented by: Melissa Frick, MD (Session 75 – Monday, 11:25 a.m. – 11:35 a.m.)
By Benjamin King, MD

Stereotactic body radiation therapy (SBRT) has proven successful as a definitive treatment for early stage lung cancer. However, while SBRT can achieve superb local control in lung cancer, late locoregional and distant failure is a problem in up to 35% of patients. One theory is that this distant failure may be due to existing micrometastatic burden even prior to local therapy. Circulating tumor cells (CTCs) are a promising new technology to help noninvasively assess for micrometastatic disease that imaging alone may miss.

In this abstract, the authors describe a prospective trial that measured pre-treatment CTC values prior to SBRT for early stage NSCLC. Simple CTC positivity did not correlate with failure but a specific cutoff concentration of 5 CTCs/ml was predictive of distant failure. With that cutoff value, they stratified patients into favorable and unfavorable risk groups. At two years median follow up, the unfavorable group with high CTC concentrations had a four times higher risk of nodal and distant failures with HR 3.92 and 4.29 respectively.

CTCs may help identify subsets of at-risk patients that imaging and other traditional surrogates like stage or size of primary may have missed. We could then offer these patients dose intensified treatment with regard to systemic therapy. One could even imagine future studies for CTCs in the oligometastatic or recurrent setting.