In vivo selection of highly metastatic human lung cancer cells. A, In vivo selection scheme. Parental human SPC-A-1 lung cancer cells were subcutaneously injected into NOD/SCID mice. When the subcutaneous tumour developed, small pieces of tumour tissue were implanted into the s.c. sites of new recipient mice in the first generation of mouse models, and primary tumours were excised 4 weeks later. Fourteen weeks after resection, visual lung metastases were isolated and re-implanted into the s.c. region of new recipient mice for in vivo selection. Finally, after three rounds of in vivo seleciton, tumour nodules were isolated from the lungs harboring massive metastatic lesions and s.c. implanted into new recipient mice, after which the primary tumour was removed to initiate in vitro culture and the SPC-A-1sci cell line was derived. B, Representative images of visual inspection of one mouse lungs for the presence of gross tumour nodules (arrows indicate) in the fourth generation. C, Representative bioluminescence images taken from the ventral side of the mice by in vivo BLI (upper) for primary tumour growth, and fluorescence images taken from the lungs of one sacrificed mouse by ex vivo BFI (lower) for spontaneous metastasis at three sequential time points from week 7 to 9, at 1-week intervals, after s.c. injection with GFP-Luc transduced SPC-A-1sci cells.