Circulating tumor cells (CTC) as a biomarker of response in patients with extensive-stage small cell lung cancer (EX-SCLC).

Abstract

e22048 Background: SCLC, a variant of lung cancer marked by early metastases, accounts for 13% of all lung cancers diagnosed in US. Despite high response rates to treatment, it is an aggressive disease with a median survival of 9-11 months for patients with EX-SCLC. Detection of CTCs is a novel laboratory technique currently in use to determine response to therapy and to predict prognosis in breast, colorectal and prostate cancer. We initiated a study to study the role of CTC as a biomarker of response and relapse in patients with EX-SCLC. Methods: We collected blood sample from chemotherapy naïve patients with EX-SCLC prior to initiation of therapy, following completion of systemic therapy, follow up every 6-8 weeks and at relapse. The CTC was determined using the Cell Search system in a central laboratory. The study was conducted in 4 different sites and it was reviewed and approved by respective Research Review Committee and IRBs. Results: We enrolled 27 patients with EX-SCLC, 1 was excluded due ineligibility, all patients were treated with platinum and etoposide. We observed partial response in 16 patients (61%), stable disease in 3 patients, 1 with progression of disease and not assessed in 7 patients (5 deceased, 2 not available); the baseline CTC of 2 patient were not measured (one due instrument failure and one due insufficient blood). The overall median number of CTCs in 24 patients measured at baseline and post-tx was 75 (range 0 to 3430) and 2 (range 0 to 526), respectively. A significant reduction in CTCs from baseline to post-tx was identified; for the 14 subjects with pre and post treatment CTC, the median reduction was 51.5% (51.5% decrease, range -2904% to +5%, p< 0.001). Conclusions: We were able to demonstrate feasibility of using CTC as a biomarker of response in patients with EX-SCLC in clinical setting. CTC could be a useful biomarker in the management of SCLC to predict response to therapy.