During my PhD I used flow cytometry assay with FITC conjugated lectins. Since cancerous progression is associated with changes in carbohydrate composition on cell surface you can detect two populations: a cancerous population with high binding of lectin and a normal population with low binding of lectin. It's a fast one-day high-throughput assay.
I agree with responses by Satish and Andre. However, I would like to add that the C3H10T1/2 cells exhibit very different characteristics in culture (see link for details below). Therefore, unless you have transformed these cells with some treatment, these cells do not spontaneously transform. Consequently, it is not clear to me why would you expect a "cancer cell" in "normal" culture of these cells. Your response may allow me to address your question specifically.