Cancer

Models

The stochastic model, taking from the concept of stochastic probability, describes the development of cancer as a completely random process. The model proposes that cancer can arise in any cell of the body, including highly differentiated cells. This occurs by an accumulation of multiple mutations leading to a loss of normal control over the cellular life cycle. The multiple mutations result in the cell developing the phenotypes of cancer, developing into a tumor, and potentially metastasizing. The key features from this model are the concept that any cell in the body can become cancerous, and that any cell in the tumor mass has the ability to divide. As a result, any cell within the tumor mass should be able to metastasize or create tumors when experimentally transplanted into a mouse.

In contrast, the stem cell theory hypothesizes that mutations accumulate in somatic stem cells. The development of this theory considers two critical properties of stem cells. First, they have sufficiently long life spans to accumulate the necessary mutations. Second, they can asymmetrically divide providing cell populations that develop and maintain a tumor. This links with the concept that tumors consist of a mass of differentiated cells maintained by a small subpopulation of cancer stem cells. These populations of cancer stem cells possess the ability to develop new tumors by either metastasis or transplantation.

Understanding whether the stochastic or stem cell model is the predominant model of cancer development is essential to developing new effective therapies to prevent and treat cancer. Ideally, new therapies will more successfully target malignant cells while preserving healthy cells. With a thorough understanding of how cancer develops, maintains a tumor, and metastasizes, researchers can identify cellular markers useful in targeting treatments to malignant cells. Ongoing research in the field has begun to distinguish between these two models and provided initial evidence of potential molecular targets.

Evidence

The first model developed to describe cancer and the model initially subscribed to by most researchers was the stochastic model of cancer. However, during attempts to develop mouse models of human cancer, researchers began to suspect that cells within a tumor mass might have different properties than had been originally anticipated. Attempts to develop tumors in mice required the injection of a large number of malignant cells to guarantee tumor development. The idea that so many cells would be necessary to develop a tumor was not consistent with the rates of metastasis of many forms of cancer in humans.

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