Elsevier

Lung Cancer

Volume 112, October 2017, Pages 118-125
Lung Cancer

Circulating tumor cells as a predictive biomarker in patients with small cell lung cancer undergoing chemotherapy

https://doi.org/10.1016/j.lungcan.2017.08.008Get rights and content

Highlights

  • CTCs are detectable at baseline in SCLC and correlate with stage and outcomes.

  • CTCs were measured at baseline, prior to each chemotherapy cycle, and at relapse.

  • CTCs added independent prognostic information for patients undergoing chemotherapy.

  • The first trial to prospectively evaluate markers of both DNA damage and apoptosis on CTC.

  • We show that assessment of these biomarkers on CTCs was feasible.

Abstract

Background

There are no biomarkers for assessment of disease burden or activity of therapy in SCLC.

Patients and methods

We conducted a prospective study enumerating serial CTCs in patients with newly diagnosed limited disease (LD) and extensive stage (ED) SCLC. CTCs demonstrating DNA damage and apoptosis based on γH2AX and M30 staining were also assessed. We correlated CTC number with disease stage, survival outcomes and tumor burden by RECIST.

Results

Between 03/2011-10/2013, 50 evaluable patients were enrolled (20 LD). Baseline CTC number was higher for ED (median CTC 71 vs. 1.5 for LD; p 0.0004). Patients with <5 CTC had longer PFS but not OS (11 vs. 6.7 months, p 0.0259 and 15.5 vs. 12.9 months, p 0.4357). A higher cutoff (CTC < 50 or CTC  50) was significantly correlated with both OS (20.2 vs. 11.8 months, p 0.0116) and PFS (10 vs. 4.8 months, p 0.0002). Patients with <5 CTC on day 1 of cycle 2 had longer PFS (10 vs. 3.17 months, p < 0.001) and OS (18 vs. 9 months, p 0.0001). Patients with an increase in γ2HAX-positive CTCs after chemotherapy had longer OS compared to patients without an increase (25.3 vs. 9 months, p 0.15).

Conclusions

This study demonstrates that CTCs at baseline and Cycle 2 of chemotherapy correlate with disease stage and survival in patients with SCLC, suggesting that CTCs may be used as a surrogate biomarker for clinical response. Confirmatory prospective clinical trials are needed before we can incorporate routine evaluation of CTCs into clinical practice.

Introduction

Small Cell Lung Cancer (SCLC) accounts for approximately 13% of all lung cancer cases [1], [2] Most SCLC patients present with distant metastases and have a poor prognosis. All previous drug development strategies in SCLC have been typified by therapeutic empiricism without a sophisticated strategy for patient selection. Better biomarkers to identify patients destined to do well or poorly as early as possible in the treatment course could be very useful to accelerate the development of new agents. Given the difficulty in obtaining enough analyzable tissue from SCLC patients, there is an unmet need for a noninvasive biomarker that is prognostic and/or predictive of benefit with new therapeutic agents.

One simple user-friendly way to non-invasively obtain cancer cells for some cancer types is through analysis of circulating tumor cells (CTCs). CTCs can be detected by “CellSearch®”, that enriches and enumerates CTCs utilizing an EpCAM-immunoferrofluid magnetic separation and differential staining of circulating white blood cells vs. cells of epithelial origin by selecting cells that are negative for CD45 (a pan leukocyte antibody) and positive with pan cytokeratin (CK) and nuclear material (DAPI) [3], [4], [5], [6], [7], [8].

Although it has been very difficult to identify CTCs in non-small cell lung cancer [9], this does not appear to be the case for SCLC. Hou et al. reported detection of CTCs in 85% of patients with SCLC using CellSearch®; CTC number fell following chemotherapy [10]. In another study, Naito et al. also detected ≥2 CTCs/7.5 ml in 68% of patients with SCLC, and found that patients with <8 CTC lived longer than those with ≥8 CTC at baseline, after treatment, and at the time of relapse [11]. Normanno et al. and Hilermann et al., each individually reported detection of at least one CTC in 90% and 84% of patients with SCLC at baseline [12], [13], [14]]. Change in CTC number following chemotherapy provided additional clinical information in the Normanno study (a significant decline in CTC count, after one cycle of chemotherapy was associated with a lower risk of death (HR 0.24, 95% CI 0.09–0.61)) [12]. Similarly, Hiltermann and colleagues showed that CTC count after one cycle of chemotherapy served as the strongest predictor of overall survival (HR 5.7; 95% CI 1.7–18.9; p = 0.004). Together these studies demonstrate that capture of CTCs by CellSearch® at baseline is feasible, reproducible, and predictive of response to chemotherapy. However, practical application of CTCs in SCLC remains limited as the previous studies have been restricted to certain subsets of SCLC (for example, the Normanno et al. study evaluated patients with extensive stage disease alone) and variable CTC cutoffs have been utilized for prognostic determination.

In addition to being able to enumerate CTCs, CellSearch® also allows one to obtain additional pharmacodynamic information using immunohistochemical markers. The key criteria for such markers are that an antibody exists that can be used to stain cells on the CellSearch® platform and that the marker should be a validated measure of chemotherapy-induced DNA damage and/or cell death/apoptosis. Based on previous literature using, CellSearch®, two such makers that fit these criteria are the DNA damage marker γH2AX [15], [16] and apoptosis marker M30 [17], [18].

Phosphorylated H2AX (γH2AX) is a marker of DNA damage and appears in the nucleus within minutes in a dose-dependent manner in cells treated with cytotoxic chemotherapy [15]. Wang et al. demonstrated that the percentage of γH2AX-positive cells increased in epithelial tumor cell lines [MCF7 (human breast adenocarcinoma), PC-3 (human prostate adenocarcinoma), HT-29 (human colorectal adenocarcinoma), and SKOV-3 (human ovarian adenocarcinoma)] treated with therapeutic concentrations of topotecan ex vivo. In vivo, the percent of γH2AX-positive CTCs increased post-treatment from a mean of 2% at baseline to 38% after a single day of chemotherapy in patients with a variety of advanced malignancies enrolled in phase I clinical trials [16].

M30 antibody recognizes a caspase-cleaved neoepitope of Cytokeratin 18 that is only revealed during apoptosis. M30 positive CTCs can be detected in patients with various malignancies. Rossi et al. sequentially assessed CTCs and M30-positive CTCs in breast cancer patients. Overall the number of total and M30-positive CTC decreased during treatment in six and increased in two of eight patients. They suggested that changes in the number of M30 positive CTCs may predict response to therapy [17], [18].

We designed this study to prospectively assess the relationship of CTCs to disease stage, and survival, at baseline and prior to each chemotherapy cycle. In addition, our study sought to evaluate the applicability of CTCs as a potential, non-invasive, pharmacodynamic biomarker.

Section snippets

Study design

We conducted a prospective trial at Abramson Cancer Center of the University of Pennsylvania, Philadelphia. Adult patients with a diagnosis of small cell lung cancer with measurable disease, receiving first line chemotherapy or chemoradiation, were included. All patients signed informed consent. The study was reviewed and approved by the Institutional Review Board at the University of Pennsylvania.

Peripheral blood was collected for CTC evaluation before the initiation of therapy (baseline) and

Patient characteristics

Between March 2011 and October 2013, 50 patients were enrolled. Patient characteristics are displayed in Table 1. At the time of this analysis, 37 patients had disease progression (76%) and 33 patients (66%) had died.

SCLC and overall survival

The average length of follow up for all patients on the study was 15.8 months. Median PFS of the entire population was 7.3 months, and median OS was 14.9 months (Fig. 1A and B). Median PFS was significantly higher for LD compared with ED (12.7 months vs. 5.8 months, p value <0.0001

Discussion

Our single center prospective study confirms that CTCs can be detected and followed serially in most patients with SCLC using the CellSearch® technology. CellSearch® is the most widely used method for CTC detection. Despite widespread availability and common use in other malignancies like breast cancer and prostate cancer, its utility in patients with SCLC is not well established. CTCs have been evaluated as a biomarker in SCLC in several other studies [10], [11], [13], [18]. Similar to these

Conflicts of interest disclosure

In the interest of full transparency, on behalf of my co-authors and myself we would like to disclose that there are no potential conflicts of interest and all authors have read and approved the manuscript.

References (18)

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Supported by Grant from American Cancer Society, IRG 78 002 31.

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