Cancer Is Not Just in Your Genes: Be Aware of These Key Culprits

No longer viewed solely as a genetic disease, cancer is increasingly understood as a condition influenced by modifiable lifestyle factors. The American Cancer Society states that an estimated 40 percent of all cancers in the United States are associated with potentially modifiable risk factors, including obesity, poor diet, and physical inactivity.

In a Vital Signs interview, Dr. Jason Fung, bestselling author of “The Cancer Code,” challenges the traditional gene-centric view—instead pointing to a complex interplay between cellular function and environmental factors. He advocates for strengthening the immune system and improving the body’s “cellular soil” through lifestyle changes, particularly diet, as a major tenet of cancer prevention.

Most Cancers Are Not Hereditary

Historically, cancer was understood through the somatic mutation theory, proposed by Theodor Boveri in the early 20th century, which linked chromosomal abnormalities to uncontrolled cell growth. High-profile cases, such as Angelina Jolie’s 2013 preventive double mastectomy after testing positive for a BRCA1 gene mutation, reinforced the idea that genetics dominate cancer risk.

However, emerging research has shown that hereditary factors account for only a small fraction of cancer cases. Instead, the environment in which genes operate—for example, shaped by lifestyle choices such as smoking, diet, and obesity—plays a far larger role. According to the American Cancer Society’s Cancer Facts & Figures 2025 report, cigarette smoking accounts for the highest number of cancer deaths, highlighting that many cancers stem from modifiable lifestyle choices rather than inherited genetic factors.

In addition, cancer symptoms manifest with striking similarity across individuals—even across time, space, and geography. Breast cancer, for instance, displays remarkably consistent morphological traits and behavioral patterns among patients worldwide. This consistency points not to shared genetics, but to deeply embedded biological systems that reactivate under certain stresses—suggesting that common environmental and physiological triggers play a greater role than heredity in the development of most cancers.

Obesity Fuels Cancer Risk

In 2002, the International Agency for Research on Cancer identified obesity as a significant risk factor for several cancers, including esophageal, colon, endometrial, breast, and pancreatic cancers. This conclusion links obesity to increased cancer incidence and higher mortality rates.

A comprehensive 2023 review on obesity and cancer epidemiology further reinforced this connection, reporting robust evidence of obesity’s role across numerous cancer types. When combined with a poor diet, obesity was estimated to account for roughly 30 percent of cancer cases.

People who are overweight or obese tend to have higher insulin levels, which is a contributing factor to breast cancer. Therefore, by focusing on the metabolic and hormonal environment in which cancer develops and adopting a healthy diet, we can lower the risk and make a real difference.

Cancer as Response to Chronic Damage

Fung describes cancer as a cellular, evolutionary “step backward” to a single-cell way of living, or a breakdown of cellular order—a regression to a more primitive, survival-driven state. When cells are under chronic damage, they abandon their cooperative roles within the body and invade nearby tissues to compete for blood supply and nutrients. This form of cellular anarchy reflects a regression where survival outweighs cooperation.

Poor diet, toxins, smoking, chronic inflammation, aging, or other factors can trigger those chronic cellular damages.

According to Fung, addressing cancer should not focus solely on eradicating malignant cells but also on restoring cellular harmony and improving the biological environment that sustains health. The goal is to make the “soil” inhospitable for cancer’s growth.

He suggests strategies such as:

• Reducing Chronic Inflammation: By limiting processed foods, refined sugars, and excessive omega-6 oils, while promoting anti-inflammatory foods like vegetables, omega-3-rich fish, and olive oil.
• Supporting Immune Function: Through restorative sleep, regular physical activity, nutrient-rich diets, and minimizing chronic stress. Fasting and metabolic therapies can help rebalance insulin and glucose metabolism, thereby restoring immune surveillance.
• Managing Stress: Since prolonged stress hormones impair both immunity and cellular repair, stress reduction practices such as meditation and breathing exercises can help.
• Avoiding Toxins and Carcinogens: Including tobacco, alcohol, and environmental pollutants.

In essence, Fung suggests that by improving the environment in which cells live—rather than only targeting cancer cells themselves—we can reduce the conditions that allow cancer to thrive.

The Immune System’s Role

In most cases, the immune system detects and eliminates abnormal cells in the body before they can develop into cancer cells. Fung calls this ongoing process “cancer surveillance,” which plays a vital role in preventing cancer from growing into a detectable or dangerous disease.

Fung indicates that this is why transplant programs are so vigilant about monitoring for cancer, citing a striking example of the phenomenon involving a melanoma patient. Although the visible cancer had been removed and the patient appeared to be in remission, the cancer cells remained dormant and tightly controlled by the immune system. Years later, the individual died in an accident, and their organs were donated. One of the recipients developed widespread melanoma because once the immune system was suppressed to prevent organ rejection, those hidden cancer cells were no longer kept in check.

Immunotherapy Advances

In past years, cancer treatments such as surgery, radiation, and chemotherapy have focused on removing tumors and killing cells indiscriminately. While such an aggressive form of treatment may reduce tumor size, it often harms healthy tissue as well, and it doesn’t address the root of the disease.

In contrast, immunotherapy represents a transformative advancement by targeting the underlying dysfunction. Therapies such as CAR-T cell therapy harness a patient’s immune cells, reprogramming them to recognize and destroy cancer cells. By “uncloaking” cancer cells—which often develop mechanisms to evade immune detection—these treatments enhance the body’s natural defenses, restoring its ability to fight the disease effectively.

More to Explore

Cancer is a complex disease with many contributing factors, which makes it difficult to predict or prevent. For instance, being overweight increases the risk, but it doesn’t guarantee someone will develop cancer. Likewise, being slender lowers the risk, but it doesn’t make a person immune. Similarly, smoking is a major risk factor for lung cancer, but not all smokers develop the disease. It’s one of many risk factors—not a direct cause-and-effect relationship like with infectious diseases.