Circulating Tumor Cells Identify Early Recurrence in Patients with Non-Small Cell Lung Cancer Undergoing Radical Resection

Conclusion

CTCs can be detected and characterized in patients undergoing radical resection for non-small cell lung cancer. Their presence might be used to identify patients with increased risk of early recurrence.

Discussion

The clinical value of CTCs detection in patients´ blood is becoming increasingly important as cancer biomarker research [14]. The main goal of CTC detection in early stages NSCLC is to identify patients with a high risk of recurrence after surgery in order to adopt the best strategy for treatment and follow up.

In this prospective study we found that CTC presence after surgery is associated with early recurrence and a shorter disease free survival in patients with surgical treatment of NSCLC

In our analysis, which enrolled 56 patients who had undergone radical surgery for previously untreated NSCLC, detection rate was significantly lower one month after surgery (32.14% vs. 51.79% before surgery, p = 0.034).

There are only a few studies that evaluate the prognostic significance of CTCs detection in resected NSCLC and even less that perform a second detection after surgery [10–13]. In a study by Hofman et al. [10] including I-IV stages resectable patients, the detection rate is similar to ours (49%). They perform only one presurgery CTCs detection employing a technique based on isolation by size (ISET technique), and they found that a CTC count of 50 cells or more is correlated with a worse overall and disease free survival. In another small scale study by Rolle et al. [11] 30 patients with resectable NSCLC were examined using the MAINTRAC technique, based on cytometric assay. CTCs were determined 2 weeks and 5 months after surgery. The CTCs count was compared to prognosis and patients with continuously increasing in median CTC-count post-operatively were shown to be at a higher risk of relapse.

Only two more prospective studies [12,13] using CellSearch system to detect CTCs, have reported so far the clinical impact of CTCs detection in peripheral blood before and after surgery. However, both failed to demonstrate any difference in either survival or recurrence. Both of them analyzed CTCs presence in blood immediately after surgery. Sawabata´s group [13] observed that CTCs disappeared ten days after operations. In fact, it is well known that during surgery a large number of CTCs can be shed into the blood stream but it has not been demonstrated that these cells are involved in the development of any future metastases. A number of them are apoptotic and many of them will be eliminated by the immune system [14]. That is why we think that for a real assessment of CTC presence after surgery the second detection must be performed at least 3 weeks after the operation.

Indeed we found a significant decrease in CTCs detection rate one month after surgery: CTCs were not detected in peripheral blood in almost 70% of patients in the second detection, and 25 out of 29 patients with CTCs presence at baseline showed a decrease in CTC count. This finding can be one of the reasons that explains why surgery remains the best treatment option in early stages.

The presence of CTCs one month after radical resection might indicate the presence of another source of CTCs not removed by surgery, such as those undetectable by conventional methods.

In accordance with that, in our study patients with detectable CTCs in peripheral blood one month after surgery presented a worse prognosis. Presence of CTCs after surgery (CTC2) was significantly associated with recurrence and DFS, so that CTC2 positive patients presented a higher risk of recurrence (p = 0.018) and a shorter DFS. The one year DFS rate was 51% in CTC2 positive patients compared to 87% for CTC2 negative patients (log rank test p = 0.008). CTC level was higher in patients with recurrence but the difference was not siginificant (mean number of 1 cell per 10 ml for patients with recurrence vs 0.5 per 10 ml for patients who did not develop a recurrence, p = 0.13).The mere presence of at least one CTCs after surgery (CTC2+) was significantly associated with patient prognosis in our analisys. Our results reflect that the presence of post-surgery CTCs (HR,5.75; 95% CI 1.50–21.95; p = 0.01) and nodal status (HR,3.38; 95% CI 1.04–10.9; p = 0.043) are good independent prognostic factors for DFS in multivariate analysis.

CTCs count in post-surgical samples showed an association with the max SUV of PET scan (p = .046). This is the first time that this association has been analysed. Max Suv value of PET scan has been associated with a worse prognoses and it could be related to a higher risk of postoperative CTCs presence.

Besides detection, CTCs characterization could be important to assess prognosis and the type of adjuvant treatment or to determine the best option of treatment for recurrent disease. EGFR expression was detected in 89.7% and 38.9% of CTCs isolated from blood samples taken before and after surgery, respectively. Regarding the prognostic siginificance of EGFR expression we found that 28.6% of patients with EGFR+CTC2+ experienced a recurrence compared to 63.6% for EGFR-CTC2+, but the difference was not significant. In our study CTCs detection after surgery was associated with worse prognosis but EGFR characterization was not. Probably a large-scale study may determine the EGFR expression influence in these patients prognosis.

On the other hand, it is worth stressing that current methodologies allow us to detect only the subpopulation of CTCs positive for epithelial markers, but not subpopulations positive for expression of mesenchymal markers and with a semi mesenchymal or mesenchymal phenotype. These phenotypes have been correlated with bad prognosis in different type of tumors [21] and therefore they should be analysed in future studies in order to achieve a better understanding of the prognostic role of CTCs in lung cancer.

To our knowledge, this study is the first large data set to validate CTCs as a prognostic marker performing postsurgery detection and to assess not only the risk of early recurrence but also to determine CTCs as predictive markers through their characterization.

In conclusion, our results show that CTCs can be detected in the blood of patients undergoing radical surgery for NSCLC. CTC detection after surgery could be an important prognostic marker contributing to risk stratification by identifying patients with a higher risk of early recurrence. Further studies are warranted to validate these results.

References