Growth in agar and tumor formation in immunologically incompetent mice as criteria for keratinocyte transformation

Established cell lines from 8 human squamous cell carcinomas (SCC) together with normal human keratinocytes, have been investigated for their ability to grow in soft agar and as xenografts when injected as a single cell suspension into immunologically incompetent mice. One of 8 SCC lines formed colonies with efficiencies greater than 1% in soft agar, and only 2 formed progressively growing tumors when injected into animals. It is concluded that these 2 criteria are not reliable markers of malignant transformation in squamous epithelia unless cytological criteria are also applied.