[Chann]

I'm stumped at this question, I can only think that the question is answering itself ?

Question: Cancerous tissue is composed of cells undergoing uncontrolled, rapid cell division. How could you develop a procedure to identify cancerous tissue by counting the number of cells undergoing mitosis?

[Microscope.com]

Well, you could calculate a normalized rate of "healthy" cell division (for the type of cell as some cells (e.g. liver versus pancreas) may divide faster or slower in mitosis) and then set a constant based on the averages that, if exceeded, would indicate the cells being analyzed should be scrutinized further as possible cancerous.

This is a "shoot from the hip" answer but is a logical methodology.

[ScienceShark]

On the other hand by using mitotic marker you should see more mitotic cells in comparison to the normal tissue. The cancer cells go to immature mitosis more often so the amount of this cells should be more in particular time point.