What percentage of cancers are caused by genetic mutations?

What Percentage of Cancers Are Caused by Genetic Mutations?

Approximately 5-10% of all cancers are caused by inherited genetic mutations, while the remaining 90-95% are attributed to environmental and lifestyle factors. 1, 2

The Genetic Contribution to Cancer

Inherited vs. Sporadic Cancer

• Only 5-10% of cancers arise from inherited germline mutations that are passed from parent to child, conferring significantly increased cancer risk across generations. 1, 2

• The vast majority (90-95%) of cancers are sporadic, resulting from acquired somatic mutations caused by environmental exposures, lifestyle factors, and aging rather than inherited genetic predisposition. 1, 2

• Environmental and lifestyle factors that drive the majority of cancers include tobacco use (25-30% of cancer deaths), diet (30-35%), infections (15-20%), and other factors like radiation, obesity, physical inactivity, and environmental pollutants. 2

Specific Cancer Types and Hereditary Contribution

Colorectal Cancer:

• Between 5-15% of colorectal cancer patients develop disease based on underlying genetic predisposition, often from single-gene mutations. 3
• The remaining 85-95% are sporadic cases influenced by lifestyle and environmental factors. 3

Breast Cancer:

• Familial susceptibility accounts for approximately 25% of all breast cancer cases. 4
• However, BRCA1 and BRCA2 mutations explain only about 15% of familial breast cancers, meaning more than 70% of familial cases remain genetically unexplained. 3, 4
• In unselected breast cancer patients, BRCA1 mutations occur in <1-7% and BRCA2 in 1-3%. 4

Ovarian Cancer:

• The likelihood of identifying a BRCA1/2 mutation in women with ovarian cancer at any age is approximately 13-18%. 3

Endometrial Cancer:

• Approximately 5% of endometrial cancers are due to genetic mutations associated with Lynch syndrome or Cowden syndrome. 3

Male Breast Cancer:

• 15-20% of male breast cancer cases have a BRCA1/2 mutation, with BRCA2 being particularly strongly associated. 3, 5

High-Penetrance Cancer Susceptibility Genes

The known high-penetrance genes that cause hereditary cancer syndromes collectively account for no more than 25% of familial cancer cases: 3

• BRCA1 and BRCA2: Hereditary Breast-Ovarian Cancer Syndrome with 50-85% lifetime breast cancer risk 4, 6
• TP53: Li-Fraumeni Syndrome with 25% breast cancer risk by age 74 and multiple other cancer types 3
• PTEN: PTEN Hamartoma Tumor Syndrome/Cowden Syndrome with 85% lifetime breast cancer risk 3
• MLH1, MSH2, MSH6, PMS2: Hereditary Nonpolyposis Colorectal Cancer (Lynch syndrome) 3
• APC: Familial Adenomatous Polyposis 3
• CDH1: Hereditary Diffuse Gastric Cancer with 39% lifetime lobular breast cancer risk 3
• STK11: Peutz-Jeghers Syndrome with 32% breast cancer risk by age 60 3

Clinical Implications

The critical distinction is between germline (inherited) and somatic (acquired) mutations:

• All cancers are genetic diseases at the cellular level, caused by DNA alterations in cancer cells. 7, 8
• However, only 5-10% involve inherited germline mutations that can be passed to offspring. 1, 2
• The remaining 90-95% involve somatic mutations acquired during a person's lifetime from environmental mutagens and lifestyle factors. 1, 2

This has profound implications for cancer prevention:

• The majority of cancer burden is potentially preventable through lifestyle modifications including smoking cessation, healthy diet, physical activity, maintaining healthy weight, limiting alcohol, and avoiding carcinogen exposure. 1, 2
• Genetic testing and surveillance are appropriate for the small subset with strong family history or clinical features suggesting hereditary cancer syndromes. 3
• Even with negative genetic testing, family history of cancer may still indicate increased risk from shared environmental factors or unidentified genetic variants. 4