Distinction of the phenotypes of in vitro anchorage-independent soft-agar growth and in vivo tumorigenicity in the nude mouse.

The growth characteristics of LT-2 cells, an epithelial squamous cell carcinoma, clearly separate the phenotypes of anchorage-independent growth in soft agar and tumor formation in vivo. LT-2 readily grows and forms tumor nodules in the nude mouse but does not proliferate anchorage independently in soft agar. This distinction is confirmed by the observation that cells explanted from nude mouse tumor nodules and cultured in vitro still do not clone in soft agar. The human origin of tumor nodule cells was confirmed by karyotyping. LT-2 cells have an aneuploid karyotype which has persisted for 4.5 years in culture with considerable variation in chromosomal number. Passage through the nude mouse did not select for any "tumor" clone since marked chromosomal variation was still noted by cells explanted from tumor nodules. Tumor cells formed a well-differentiated skin with keratin formation in the nude mouse despite wide karotypic variations of cells and years of in vitro culture. Strict monolayer growth was noted by LT-2 cells when grown in culture flasks and also by cells explanted from tumor nodules, indicating that monolayer growth and nude mouse tumorigenicity are also separate phenotypes.