Question

Explain the steps of cancer progression in detail. Describe at least two ways the first step of cancer progression could occur.

Answer 1

Majorly, cancer is a genetic disease. It is caused by the changes to genes that control the way our cells function, and how they grow and divide.

Particularly, the so called genetic changes which cause cancer can be inherited from our parents. They can also arise during a person’s lifetime as a result of errors that occur as cells divide or because of damage to DNA caused by certain environmental exposures. Cancer-causing environmental exposures include various chemical substances, such as the chemicals in tobacco smoke, and radiation, such as ultraviolet rays from the sun.

Most importantly, the genetic changes which contribute to cancer tend to affect three main types of genes that usually known as proto-oncogenes, tumor suppressor genes, and DNA repair genes. These changes are sometimes called “drivers” of cancer.

Proto-oncogenes are involved in normal cell growth and division. However, when these genes are altered in certain ways or are more active than normal, they may become cancer-causing genes (or oncogenes), allowing cells to grow and survive when they should not.

Tumor suppressor genes are also involved in controlling cell growth and division. Cells with certain alterations in tumor suppressor genes may divide in an uncontrolled manner.

DNA repair genes are involved in fixing damaged DNA. Cells with mutations in these genes tend to develop additional mutations in other genes. Together, these mutations may cause the cells to become cancerous.

At the cellular level, the development of cancer is viewed as a multistep process involving mutation and selection for cells with progressively increasing capacity for proliferation, survival, invasion, and metastasis. The first step in the process, tumor initiation, is thought to be the result of a genetic alteration leading to abnormal proliferation of a single cell. Cell proliferation then leads to the outgrowth of a population of clonally derived tumor cells. Tumor progression continues as additional mutations occur within cells of the tumor population. Some of these mutations confer a selective advantage to the cell, such as more rapid growth, and the descendants of a cell bearing such a mutation will consequently become dominant within the tumor population. The process is called clonal selection, since a new clone of tumor cells has evolved on the basis of its increased growth rate or other properties (such as survival, invasion, or metastasis) that confer a selective advantage. Clonal selection continues throughout tumor development, so tumors continuously become more rapid-growing and increasingly malignant.

Particularly, stages of tumor progression are:

Hyperplasia - cells divide too much but appear normal

Dysplasia - the tumor cells and tissue appear abnormal

Carcinoma in situ - tumor contains primarily altered cells and is growing larger; it has not left the site of origin

Malignant Cancer - tumor has begun to invade nearby or distant tissues

Benign tumors remain in their initial location and do not invade other tissues.