What causes kidney cancer

Overview

Kidney cancer is a disease in which kidney cells grow out of control, forming a tumor. Most kidney cancers are renal cell carcinomas (RCCs), which begin in the lining of the tiny tubes (tubules) within the kidneys. The kidneys are two bean-shaped organs, each about the size of a fist, located on either side of the spine, below the ribs and behind the belly. Their main function is to filter waste products from the blood and produce urine. When kidney cells develop abnormalities in their DNA, they can begin to multiply abnormally, forming a mass known as a tumor. If these cells are cancerous, they can invade nearby tissues and spread (metastasize) to other parts of the body.

What Causes Kidney Cancer?

The exact cause of most kidney cancers is not fully understood, but it is known to be related to changes (mutations) in the DNA of kidney cells. These mutations cause cells to grow and divide uncontrollably, forming a tumor. While some mutations occur randomly during a person's life, others can be inherited. The development of kidney cancer is often a multi-step process involving the accumulation of genetic changes over time.

Risk Factors for Kidney Cancer

While the specific trigger for DNA mutations is often unknown, several factors are known to increase a person's risk of developing kidney cancer. These risk factors do not guarantee that someone will develop the disease, but they are associated with a higher incidence.

Smoking

Smoking tobacco is one of the most significant and preventable risk factors for kidney cancer. Smokers are about 2 to 3 times more likely to develop kidney cancer than non-smokers. The chemicals in tobacco smoke are absorbed into the bloodstream and can damage the DNA of kidney cells. This risk is also elevated for former smokers, although it decreases over time after quitting. Exposure to secondhand smoke also appears to increase the risk.

High Blood Pressure (Hypertension)

High blood pressure, especially when it is long-standing or poorly controlled, is another major risk factor. The exact mechanism by which hypertension contributes to kidney cancer is not fully clear, but it may involve damage to blood vessels in the kidneys or altered kidney function. Some blood pressure medications have also been investigated, but the link is generally considered weaker than that of hypertension itself.

Obesity

Being overweight or obese significantly increases the risk of developing kidney cancer. Studies suggest that obese individuals have a 25% higher risk compared to those who are at a healthy weight. The reasons for this association are complex and may involve hormonal changes, chronic inflammation, and altered growth factors associated with excess body fat.

Age and Gender

The risk of kidney cancer increases with age. It is most commonly diagnosed in people between the ages of 50 and 70. Men are also more likely to develop kidney cancer than women, although this gap has narrowed in recent years.

Certain Inherited Genetic Conditions

In a small percentage of kidney cancer cases (about 5%), the disease is linked to inherited genetic mutations passed down through families. These inherited conditions can lead to a significantly higher risk of developing kidney cancer, often at a younger age. Examples include:

• Von Hippel-Lindau (VHL) disease: A rare genetic disorder that increases the risk of tumors in various organs, including the kidneys.
• Hereditary papillary renal cell carcinoma: Caused by mutations in the MET gene.
• Hereditary leiomyomatosis and renal cell cancer (HLRCC): Associated with mutations in the FH gene.
• Birt-Hogg-Dubé (BHD) syndrome: Linked to mutations in the FLCN gene.

Genetic counseling and testing may be recommended for individuals with a strong family history of kidney cancer or those diagnosed with these syndromes.

Exposure to Certain Toxins and Chemicals

Long-term exposure to certain substances can increase the risk of kidney cancer. This is particularly relevant for individuals working in specific industries. Examples include:

• Occupational exposure: Working with certain chemicals, such as cadmium, asbestos, benzene, and some herbicides and pesticides, has been linked to an increased risk.
• Kidney disease treatments: Long-term use of certain pain relievers containing phenacetin was historically linked to kidney tumors, though this medication is no longer available in many countries. Dialysis patients, particularly those on long-term hemodialysis, have a higher risk of developing acquired cystic kidney disease (ACKD), which can sometimes lead to kidney cancer.

Other Potential Factors

Research is ongoing into other potential factors, including:

• Certain chronic kidney diseases: Conditions like acquired cystic kidney disease (ACKD) are associated with an increased risk.
• Family history: Having a close relative (parent, sibling, child) with kidney cancer increases risk, even without a known inherited syndrome.
• Race: Kidney cancer is slightly more common in Black individuals compared to White individuals, though the reasons are not fully understood and may relate to differences in risk factors like hypertension and socioeconomic status.

Understanding the Cellular Process

At a cellular level, kidney cancer begins when the DNA inside kidney cells becomes damaged. DNA contains the instructions for cell growth and division. When these instructions are altered, cells may start to grow abnormally, ignore signals to stop dividing, or fail to die when they should. This uncontrolled growth leads to the formation of a mass of cells, or tumor. If the tumor is malignant (cancerous), these cells can invade surrounding tissues and potentially spread to distant parts of the body through the bloodstream or lymphatic system. The specific genes that are mutated often differ depending on the type of kidney cancer and the individual's risk factors.

Conclusion

While many cases of kidney cancer arise without a clear cause, understanding the known risk factors allows for informed lifestyle choices and medical monitoring. Recognizing these factors can empower individuals to take steps to reduce their risk, such as quitting smoking, maintaining a healthy weight, and managing blood pressure. Early detection and diagnosis remain crucial for improving treatment outcomes.