Selective killing of circulating tumor cells prevents metastasis and extends survival

Distant metastasis is initiated by circulating tumor cells (CTCs), which are considered to be a determining factor for the degree of metastasis and the survival of cancer patients. Although CTC-based diagnostic approaches are being rapidly developed, limited studies have proven the benefits of CTC elimination, with most studies providing only hypothetical inference because of the technical difficulty in examining the effects of CTC elimination in vivo. We modified photodynamic therapy to specifically eliminate green fluorescent protein (GFP)-expressing CTCs and evaluated the therapeutic efficacy of CTC elimination. When circulating blood is illuminated with a blue laser (λ = 473 nm), the combination of GFP and photosensitizers induces a selective elimination of GFP-expressing CTCs, with limited effect on normal cells. In GFP-expressing cancer cell-infused or transplanted mice models, the treatment suppressed distant metastasis and extended the survival of the tumor-bearing mice. Taken together, CTCs are a core seed to be metastasized into secondary organs and elimination of CTCs may improve the survival of cancer patients.