title: Multistep nature of metastatic inefficiency: dormancy of solitary cells after successful extravasation and limited survival of early micrometastases.
abstract: In cancer metastasis, only a small percentage of cells released from a primary tumor successfully form distant lesions, but it is uncertain at which steps in the process cells are lost. Our goal was to determine what proportions of B16F1 melanoma cells injected intraportally to target mouse liver 1) survive and extravasate, 2) form micrometastases (4 to 16 cells) by day 3, 3) develop into macroscopic tumors by day 13, and 4) remain as solitary dormant cells. Using in vivo videomicroscopy, a novel cell accounting assay, and immunohistochemical markers for proliferation (Ki-67) and apoptosis (TUNEL), we found that 1) 80% of injected cells survived in the liver microcirculation and extravasated by day 3, 2) only a small subset of extravasated cells began to grow, with 1 in 40 forming micrometastases by day 3, 3) only a small subset of micrometastases continued to grow, with 1 in 100 progressing to form macroscopic tumors by day 13 (in fact, most micrometastases disappeared), and 4) 36% of injected cells remained by day 13 as solitary cancer cells, most of which were dormant (proliferation, 2%; apoptosis, 3%; in contrast to cells within macroscopic tumors: proliferation, 91%; apoptosis/necrosis, 6%). Thus, in this model, metastatic inefficiency is principally determined by two distinct aspects of cell growth after extravasation: failure of solitary cells to initiate growth and failure of early micrometastases to continue growth into macroscopic tumors.
authors.affiliation: Department of Medical Biophysics, University of Western Ontario, London Regional Cancer Centre, Canada.
authors.forename: K J
authors.initials: KJ
authors.lastname: Luzzi
authors.forename: I C
authors.initials: IC
authors.lastname: MacDonald
authors.forename: E E
authors.initials: EE
authors.lastname: Schmidt
authors.forename: N
authors.initials: N
authors.lastname: Kerkvliet
authors.forename: V L
authors.initials: VL
authors.lastname: Morris
authors.forename: A F
authors.initials: AF
authors.lastname: Chambers
authors.forename: A C
authors.initials: AC
authors.lastname: Groom
mesh_terms: D000818:Animals; D017209:Apoptosis; D002470:Cell Survival; D005260:Female; D019394:Ki-67 Antigen / Q000378:metabolism; D008099:Liver / Q000098:blood supply* / Q000378:metabolism / Q000473:pathology; D008113:Liver Neoplasms / Q000473:pathology / Q000556:secondary*; D008546:Melanoma, Experimental / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008833:Microcirculation / Q000502:physiology*; D018715:Microscopy, Video; D009362:Neoplasm Metastasis / Q000473:pathology*; D009360:Neoplastic Cells, Circulating / Q000378:metabolism / Q000473:pathology*; D009418:S100 Proteins / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D019394:Ki-67 Antigen; D009418:S100 Proteins