How Cancer Occurs

How Cancer Occurs

As an oncologist, I’ve often been asked by my patients, “How does cancer occur?” It’s a question that sparks concern and curiosity, as understanding the origins of cancer can help in comprehending the disease and the importance of early detection and prevention. This blog aims to elucidate how cancer occurs, diving into the biological mechanisms and causes that lead to the development of this complex and often devastating illness.

Introduction to Cancer

Cancer is a group of diseases characterized by the uncontrolled growth and spread of abnormal cells. When these cells proliferate uncontrollably, they can form tumors, invade nearby tissues, and spread to other parts of the body through the bloodstream or lymphatic system—a process known as metastasis. To truly grasp how cancer occurs, we need to explore the cellular and genetic changes that drive this process.

How Cancer Occurs at the Cellular Level

To understand how cancer occurs, it’s essential to look at the fundamental unit of life: the cell. Our bodies are composed of trillions of cells, each governed by a complex set of instructions encoded in our DNA. These instructions regulate cell growth, division, and death. When these instructions go awry, cancer can develop.

The Role of DNA Mutations

Cancer begins with mutations in the DNA of a cell. DNA mutations can occur due to various factors, including environmental exposures, lifestyle choices, and inherited genetic predispositions. These mutations disrupt the normal regulatory processes of the cell, leading to uncontrolled growth.

  1. Oncogenes and Tumor Suppressor Genes:
    • Oncogenes: These are genes that, when mutated, become overactive and drive the cell to proliferate uncontrollably. Imagine a car with a stuck accelerator pedal.
    • Tumor Suppressor Genes: These genes normally act as brakes to cell division. When they are mutated or inactivated, the cell loses its ability to control growth. Think of a car with failed brakes.

Both types of mutations are crucial in understanding how cancer occurs. For cancer to develop, typically, both oncogenes are activated and tumor suppressor genes are inactivated.

The Process of Cell Division

To further illustrate how cancer occurs, consider the process of cell division. Normally, cells divide in a regulated manner to replace old or damaged cells. However, when mutations disrupt this regulation, cells begin to divide uncontrollably. This unregulated division results in the formation of a mass of cells or a tumor.

How Cancer Occurs Through Carcinogens

Carcinogens are substances that can cause cancer by inducing mutations in the DNA. Understanding how cancer occurs often involves studying these carcinogens. They can be categorized into several types:

  1. Chemical Carcinogens: These include substances like tobacco smoke, asbestos, and certain dyes. For instance, smoking introduces a multitude of harmful chemicals that can damage DNA in lung cells, leading to mutations.
  2. Physical Carcinogens: Ultraviolet (UV) radiation from the sun and ionizing radiation from X-rays are prime examples. UV radiation can cause skin cells to mutate, resulting in skin cancers such as melanoma.
  3. Biological Carcinogens: Certain viruses, bacteria, and parasites can lead to cancer. Human papillomavirus (HPV) is linked to cervical cancer, while Hepatitis B and C viruses are associated with liver cancer.

These carcinogens cause changes in cellular DNA, contributing to the cascade of events that lead to cancer. Avoiding exposure to known carcinogens is a key strategy in cancer prevention.

Genetic Predisposition and Inherited Mutations

While environmental factors play a significant role, genetics also contribute to how cancer occurs. Some individuals inherit mutations from their parents that predispose them to cancer. For instance, mutations in the BRCA1 and BRCA2 genes significantly increase the risk of breast and ovarian cancers.

Familial Cancer Syndromes

Certain families have higher incidences of specific cancers due to inherited genetic mutations. These familial cancer syndromes provide valuable insights into how cancer occurs and highlight the importance of genetic counseling and testing for at-risk individuals.

The Multistep Process of Carcinogenesis

Cancer development is a multistep process known as carcinogenesis. This process can be divided into three stages:

  1. Initiation: This is the first step in how cancer occurs, where a cell’s DNA is damaged by a carcinogen or due to spontaneous mutations. This initiated cell has the potential to become cancerous.
  2. Promotion: In this stage, the initiated cell is stimulated to proliferate. This can be influenced by factors such as hormones or chronic inflammation. The promotion stage involves the expansion of these abnormal cells.
  3. Progression: The final stage is marked by further genetic changes that lead to malignant transformation. The cells acquire the ability to invade surrounding tissues and spread to distant sites.

Understanding these stages helps us comprehend how cancer occurs and progresses, emphasizing the importance of early intervention and treatment.

The Role of the Immune System

The immune system plays a crucial role in identifying and destroying abnormal cells. However, cancer cells can evade immune surveillance through various mechanisms, contributing to how cancer occurs and persists in the body.

Immune Evasion

Cancer cells may produce substances that suppress immune responses or create an environment that protects them from immune attack. Understanding how cancer occurs in the context of immune evasion has led to the development of immunotherapies, which aim to boost the body’s natural defenses against cancer.

How Lifestyle Choices Influence Cancer Risk

Lifestyle choices significantly impact how cancer occurs. Factors such as diet, physical activity, alcohol consumption, and tobacco use can influence the likelihood of developing cancer.

Diet and Physical Activity

A diet high in processed foods, red meats, and low in fruits and vegetables can increase cancer risk. Conversely, a balanced diet rich in antioxidants can reduce this risk. Regular physical activity helps maintain a healthy weight and hormone levels, both of which are protective against cancer.

Alcohol and Tobacco Use

Excessive alcohol consumption is linked to several cancers, including liver, breast, and colorectal cancers. Tobacco use is one of the leading causes of cancer, particularly lung cancer. Quitting smoking and limiting alcohol intake are critical steps in reducing cancer risk.


As an oncologist, I am committed to helping my patients understand how cancer occurs. By exploring the mechanisms and causes, we can appreciate the complexity of this disease and the importance of prevention, early detection, and treatment. Whether through avoiding carcinogens, adopting healthier lifestyles, or utilizing advancements in genetic testing and immunotherapy, we have multiple strategies to combat cancer and improve patient outcomes. Understanding how cancer occurs empowers us to take proactive steps towards a healthier future.