Circulating Tumor Cells for the Monitoring of Lung Cancer Therapies

Lung cancer, as one of the most prevalent and lethal malignancies, requires immediate and effective therapeutic solutions. Therefore, additional innovative methods are continually sought to achieve optimal treatment outcomes. Various markers are used to select the most effective therapies, assess clinical responses, and facilitate follow-up care for the patients. Circulating tumor cells (CTCs) remain a valuable biomarker in clinical management of cancer patients due to the range of information they provide and their high prognostic and predictive potential in monitoring anticancer therapy. CTCs constitute a heterogeneous population of cancer cells that undergo an epithelial-to-mesenchymal transition (EMT), are shed from the tumor mass, and migrate through the peripheral blood, ultimately causing metastases. In this literature review, we focus on the biological, biochemical, and biophysical properties of CTCs, specifically from the perspective of the design of CTC enumeration technologies. Furthermore, we combine the available data on the application of CTC count in monitoring various treatment modalities in lung cancer, including radiotherapy, chemotherapy, tyrosine kinase inhibitors, and immunotherapy. Although many published reports indicate that an increased number of CTCs in blood samples of lung cancer patients correlates with worse treatment outcomes, several limitations hinder the widespread usage of CTCs in the clinical setting.