What is cancer?

A cancer diagnosis can stir up fear – fear of the loss of life, as well as fear of changes to quality of life.

But it can also cause you to fear the unknown. And ask questions like: What is cancer? What is happening inside my body?

As a breast medical oncologist at MD Anderson, Jason Mouabbi, M.D., often hears these questions from patients. “It’s important to demystify cancer so that we can move forward confidently in your treatment plan and meet your treatment goals,” he says.

Cancer occurs when cells divide uncontrollably

Cell division is normal. It’s how the body grows and heals. But this cell division is highly regulated. “The body sends signals to cells to start dividing and another signal to stop,” Mouabbi says. The body also has regulations to ensure cells don’t divide on their own.

The signals that trigger cell division are produced by genes known as proto-oncogenes. Genes that produce the signals to stop cell division are called tumor suppressor genes.

Rapid cell division leads to mutations that can become cancer

As cells divide, errors can occur. These are called mutations.

Mouabbi suggests thinking of cell division as folding a stack of paper.

“If you had a week to fold 15 pieces of paper, you could fold them identically. Now, if you only have 10 seconds for the same task, you can’t be as precise. You may just ball up some pieces up,” he says.

The same thing happens with cells. As cells divide more quickly, more errors occur.  

The body can identify and eliminate most mutations, but a small number go on to affect proto-oncogenes and tumor suppressor genes. If a mutation affects the proto-oncogenes, a cell will have so many signals that it will start dividing uncontrollability. Or, it won’t have the checkpoint mechanisms to stop growth because the tumor suppressor genes have been altered.

“The loss of control of these genes is what leads to cancer,” Mouabbi says.  

There are six hallmarks of cancer cells

Cancer originates from a normal cell in our body. But there are six factors that differentiate cancer cells from normal cells, Mouabbi says.

1. They’re self-sufficient with growth signals. When a proto-oncogene mutates, a cell internally produces signals to divide. It no longer needs outside signals to grow.

2. They’re insensitive to anti-growth signals. When the body sends signals to stop dividing, the cancer cell ignores them. Cancer cells often lose their internal signals to stop growing, too.

3. They evade the immune system. One of the functions of the immune system is to find and eliminate abnormal cells. But immunologist Jim Allison, Ph.D., discovered a secret handshake between the immune system and cancer, which allows cancer cells escape detection. Allison won a Nobel Prize for his work, which led to the discovery of immunotherapy. Immune checkpoint inhibitors are drugs that work by undoing this truce and unleashing the immune system to destroy cancer cells.

4. The cells are immortal. The more quickly cells divide, the more mutations that are introduced. Mutated cells gain new function, one of which leads to cells extending their lifespan. In the 1950s, a woman named Henrietta Lacks was diagnosed with cervical cancer. “A few of her cancer cells were removed, grown in a petri dish and launched a revolution not only in cancer research but the entire field of medicine,” Mouabbi says. “Although she died in 1951, her cells are still growing and thriving on their own.”

5. They have sustained angiogenesis. To grow, cancer needs nutrients. So, cancer forms new blood vessels to access the bloodstream. “I tell my patients to think of it as a house built out in the middle of nowhere – you must build a road first,” Mouabbi says. Normal cells can’t develop blood vessels to bring in the nutrients they need.

6. They invade other tissue. As cancer grows and more mutations occur, cancer cells can gain a function that allows them to thrive in other locations. This is called metastasis. Although it’s been tried in the lab, normal cells can’t survive when moved from their area of origin.

Benign tumors start as cells dividing uncontrollably, but they haven’t developed the mutations that allow them to spread. However, Mouabbi says that if a benign tumor goes untouched, it will continue to change and can become malignant. “That’s why we monitor benign tumors closely, or, they’re often surgically removed,” he says.

There are four main types of cancer

Each cancer falls into one of four main types.

• Carcinoma — By far the most common type of cancer, carcinomas start in the cells that make up the lining of organs. Cancers that fall under this umbrella include lung cancer, breast cancer, esophageal cancer and so many more. Depending on the type of cells that mutate into cancer, carcinomas can be further grouped into adenocarcinomas, basal cell carcinoma and squamous cell carcinoma.
  
  
• Sarcoma — These cancers are less common. Sarcomas originate in the cells of the bones, muscles and blood vessels.
  
  
• Leukemia — When cancer starts in the cells that form our blood, which come from our bone marrow, it’s classified as a leukemia. Unlike other cancer types, leukemias usually don’t form a mass, and because it originates from the blood, they don’t need to develop blood vessels for nutrients. Instead, the mutated cells overcrowd the normal blood cells. Because of that, less oxygen is carried by red blood cells to the organs, which impacts their vital function. Overcrowding of the cells also affects the platelets. Their function is to stop bleeding. Lastly, leukemia cells prevent immune cells from doing their job, so patients have a high risk of severe infection.
  
  
• Lymphoma/myeloma — These tumors impact the white blood cells, which are found in lymphatic system. This includes the lymph nodes, bone marrow, thymus and several other organs. Unlike leukemia, lymphoma and myeloma can form a mass.

You can reduce your cancer risk

Sometimes, gene mutations are passed down from parent to child. One example is the BRCA mutation. Gene mutations can also occur naturally, by chance.

However, there are outside influences that increase the risk cell mutation and lead to a higher risk of cancer. These cancer-causing influences are called carcinogens. Mouabbi suggests avoiding tobacco products, alcohol, asbestos, radon, UV lights and processed meat, to help control your risk for cancer.

In addition, some cancers have been linked to viruses. Hepatitis B and hepatitis C can lead to liver cancer. The human papillomavirus (HPV) has been linked to cervical, anal, vaginal, vulvar, throat and penile cancers. There are vaccines for the hepatitis viruses and HPV that can prevent many -of their related cancers.   

Lastly, being overweight increases your cancer risk, so maintaining a healthy diet and staying active are important. “It’s part of a healthy lifestyle,” he says. “By doing what you can to make healthier choices, you can reduce your risk of cancer.”

Request an appointment at MD Anderson online or by calling 1-877-632-6789.