20.1: What is Cancer?

Cells and tissues must meticulously coordinate their activities for the normal functioning of the human body. Therefore, they exhibit socially responsible behavior - resting, growing, dividing, differentiating, or dying - for the organism’s benefit. Cancer arises when cells divide uncontrollably and invade other tissues or organs.

Although people have known about cancer for centuries, it was only in 1761 that Giovanni Morgagni of Padua performed a detailed autopsy of patients who died from cancer. His findings laid the foundations of the scientific discipline called Oncology, the study of cancer. To date, several scientists continue to increase our understanding of cancer and its pathology.

Cancer cells have two heritable characteristics: (1) They reproduce in defiance of the normal regulation on cell growth and division; (2) They invade and colonize territories of other cells and tissues. Cancer is a disease caused by genetic alterations. In most cases, mutations in the cell cycle regulation genes allow a cell to divide at the expense of the neighboring cells and negatively impact the host’s survival. However, cancer-causing mutations build up gradually over the organism’s lifetime. Therefore, most cancer cases are not diagnosed early in life.

In order to facilitate cancer research, several cell lines and model systems are used in cancer laboratories, while new tools are always under development. Cell lines are the cells derived from cancer patients and effectively “immortalized.” Most common examples include HeLa, OVCAR-3, and LNCaP cell lines. These cell lines are commonly used across laboratories to understand cancer pathology and aid in drug discovery. Also , several transgenic, knockout, and knock-in mice mouse models have been developed to study the onset and progression of cancer. They also aid in drug discovery, testing the drug efficacy and toxicity.

The human body is made up of over 3 trillion cells. Periodically, under the control of cell cycle regulators, these cells divide to form new cells, replacing the old or damaged cells.

Under rare instances, one of these cells might overcome the cell cycle regulation and divide uncontrollably which can disrupt the body's normal functioning.

Such abnormal cell growth may result in several related diseases, collectively known as cancer. If the spread of cancer cells is not contained, it will result in the organism’s death.

So, how does a normal cell turn cancerous? Almost every cell in a human body experiences genetic mutations. Although most of these nucleotide changes are repaired by the DNA repair enzymes, some mutations remain unchecked.

In rare instances, such unrepaired mutations may allow a cell to divide faster and survive longer than the surrounding cells.

Overtime, these mutant cells proliferate, prosper and form a visible mass of cells called tumors that are broadly categorized into two types.

Benign tumors are confined to the tissue of origin. They are usually harmless and can be surgically removed.

On the other hand, malignant tumors can break off from the primary site, invade far away tissues and form another tumor, by a process called Metastasis - a hallmark of a cancerous tumor. This entire process of transformation of a normal cell into a cancerous cell is called oncogenesis.

Cancer can arise in almost any part of the body. For example, the uncontrolled proliferation of white blood cells causes leukemia, the unhindered growth of cells from the large intestine results in colon cancer, and the abnormal cell division of soft tissues like tendons, cartilage, or muscles is referred to as sarcoma.

• Cancer - A disease of uncontrolled cell division that can invade other tissues.
• Oncology - The field of medicine concerned with the study and treatment of cancer.
• Cell Division - A process by which a cell, called the parent cell, divides into two or more cells, called daughter cells.
• Cell Cycle Regulation - It is all about the control system that ensures the correct sequence of growth, DNA replication, and division.
• Cell Lines - A cell culture developed from a single cell and therefore consisting of cells with a uniform genetic makeup.

• Define Cancer – Explain what it is (e.g., uncontrolled cell division).
• Contrast Normal cell division vs Cancerous cell division – Explain how regulation deviates (e.g., loss of control in cancer).
• Explore Examples of Cell lines – Discuss their usage in research (e.g., HeLa, OVCAR-3, and LNCaP).
• Explain Genetics of Cancer – Brief discussion of the role of mutations and inheritance in cancer.
• Apply in Context – Relationship between cancer and cell cycle regulation.

• What is cancer and how does it impact cell division?
• What are cell lines and why are they essential in research?
• How do genetic alterations contribute to the development of cancer?

• Students – Understand how cancer affects cell functioning and tissue health
• Educators – Provides a clear framework for teaching about the cell cycle and abnormal divisions.
• Researchers – Relevant for critical study of disease progression and drug discovery.
• Science Enthusiasts – Offers insights into the fascinating yet complex world of cellular biology and oncology.