Tumor Models and Their Growth Characteristics

In order to understand the nature of human tumors, we need tumor models which have many of their characteristics. In this section, I will describe three such models briefly and discuss their advantages and disadvantages. Since a key characteristic of cancerous diseases is uncontrolled growth, we will discuss their growth kinetics briefly. [For a comprehensive review of various experimental and theoretical studies on growth kinetics of tumor, the reader is referred to two excellent monographs by Steel (1977) and Swan (1977), respectively.] 

Knowledge about heat and mass transfer in tumors has been obtained using primarily three types of biological systems  

Single cells from humans and animals can be grown in culture (in vitro) or inside the body (in vivo), for example, in the peritoneal cavity. 

Studies using single cells allow precise control of the extracellular environment and, therefore, can provide useful information on the cellular uptake of drugs and cell cycle kinetics during various types of treatment. Such detailed information cannot be obtained directly from whole-tissue (e.g., solid-tumor) studies because of the heterogeneous nature of tumor blood flow and vascular structure, and a variety of host factors. However, caution must be exercised in extrapolating the information obtained from single cells to the solid tumor in vivo. 

Multicell spheroids provide an in vitro model for tumors which is intermediate in complexity between solid tumors and single cell cultures. Spheroids are three-dimensional, spherical clusters of a variety of animal and human cells about 0.1-1 mm in diameter. Spheroids can be grown in suspension culture, in quiescent liquid, or in semi-solid medium. 

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