Development of predictive liquid biomarkers for response to treatment in small cell lung cancer

Small cell lung cancer (SCLC), despite being initially chemosensitive, behaves aggressively and tends to progress rapidly after or during first-line chemotherapy. Predictive indicators of response to specific treatment for SCLC have not yet been established. Carter et al. had reported that they established a genetic classifier to predict whether SCLCs were “chemosensitive (sensitive relapse)” or “chemorefractory (refractory relapse)”. They used whole genome amplification products of native circulating tumor cell (CTC) from patients to develop this classifier. These CTC classifiers could accurately identify patients with SCLC as “sensitive relapse” or “refractory relapse” to first-line chemotherapy. Although this study represented a remarkable step forward in biomarker research in SCLC, classifiers obtained in the same fashion at disease progression could not predict the response to further treatment. This may imply that the inherent genetic background for the initial response to first-line chemotherapy differs from that for newly acquired resistance to treatment. In order to improve our understanding of the biological backgrounds of SCLC, extensive research into concepts such as cancer stem cells, epithelial mesenchymal transition/ mesenchymal epithelial transition, and circulating tumor microemboli might be necessary.