The determination of the kinetics of early cancer growth has received considerable attention from cancer researchers interested in reducing the time required to assess carcinogenic risk. The three main difficulties in this study are: (1) tumors can only be identified after the animal has been sacrificed, (2) each animal exhibits considerable variability in tumor sizes and (3) tumors can only be identified once they have grown above a threshold size. Thus, the only data available to the researcher summarizes the sizes of observable tumors at the time of sacrifice. In this paper, we give techniques to help the researcher decide the type of tumor growth (e.g., exponential, logistic, Gompertz), the time at which the cancerous growth began, as well as the principal source of variability in tumor sizes (either the time of the initial growth, or the rate of growth). Additional techniques can be used to decide if the rate of growth increases with time (a consequence of the increased malignancy of the tumor) or decreases with time (due to the lack of oxygenation at the core of a large tumor). These techniques are applied to data on microscopic liver tumors (often called foci) from the lab of Dr Stanley Goldfarb (Department of Pathology, University of Wisconsin-Madison).