4.4 Cancer

1. Conditions for Cancer to Develop

There are two conditions:

1. Gene mutation: turns normal cells into cells with abnormal functions, beginning carcinogenesis.
2. Immune escape: allows abnormal cells to escape control by the immune system.

On average, meeting both conditions takes more than 20 years.

1.1. Gene Mutation

Each cell has more than 20,000 genes. Several hundred are related to cancer and can be divided into oncogenes and tumor-suppressor genes.

Oncogenes promote cell growth. If they mutate, they can overstimulate cell growth. Tumor-suppressor genes inhibit cell growth. If they mutate, they may no longer be able to limit cell growth.

If both types of genes mutate, cell growth becomes uncontrolled and cancer develops.

1.2. Immune System

Cancerous cells do not necessarily lead to cancer because the immune system exists. Besides destroying pathogenic bacteria and viruses that invade the body, immune cells can also eliminate almost all mutated cells.

The struggle between cancer cells and immune cells has three stages:

1. Immune elimination
2. Immune equilibrium
3. Immune escape

2. How High Is the Risk of Cancer for Chinese People?

For the Chinese population overall, the risk of developing cancer before age 75 is 20.6%, meaning about one in five people. The figure is 23% for men and 18.3% for women.

The three cancers with the highest incidence among young people are breast cancer, cervical cancer, and thyroid cancer.

3. Cancer Risk Factors

1. Internal factors: genes
2. External factors: can be divided into five categories

Cancer incidence caused by carcinogenic factors:

Proportion of preventable factors for different cancers:

3.1. Internal Factors

If several young people in a family develop cancer, it may indicate a hereditary tumor syndrome: inherited causes lead to chromosome and gene mutations, significantly increasing the probability of certain tumors. This can be determined through genetic testing.

Can such people have children? Yes. Prenatal testing can be used to test fetal genes and decide whether to continue the pregnancy.

3.2. External Factors

3.2.1. Diet

Carcinogens are divided into four categories:

1. Group 1: confirmed carcinogens
2. Group 2A: probably carcinogenic
3. Group 2B: possibly carcinogenic
4. Group 3: suspected carcinogens without evidence

3.2.1.1. Smoking

There are 93 clearly toxic substances. Smoking can cause not only lung cancer, but also other cancers and cardiovascular disease. Smokers have a 35% probability of dying before age 65 from various diseases caused by smoking.

3.2.1.2. Alcohol

Ethanol -> acetaldehyde -> acetic acid

The intermediate product acetaldehyde is a confirmed carcinogen. People whose faces flush when drinking should be even more cautious about alcohol because they convert ethanol -> acetaldehyde efficiently but acetaldehyde -> acetic acid poorly.

3.2.1.3. Betel Nut

Persistent damage is caused by two factors:

1. Physical: rough fibers damage the oral mucosa and teeth.
2. Chemical: alkaloids and other compounds directly kill cells and cause inflammation.

Why can persistent damage cause cancer?

It is a matter of probability. After cells die, cell division and growth are stimulated to replace them. The more cells divide and grow, the more DNA replication occurs, and the greater the probability of cancer-causing mutations.

3.2.1.4. Very Hot Food

Like betel nut, it causes cell death -> cell division -> DNA replication -> increased probability of cancer.

3.2.2. Obesity

People with obesity are more likely to develop chronic inflammation. During chronic inflammation: cell death -> cell division -> DNA replication -> increased probability of cancer.

3.2.3. Exercise

What kind of exercise can help prevent cancer? Exercise unrelated to work and performed during leisure time, such as walking, running, swimming, and fitness training. Maintain half an hour per day and three hours per week.

Can muscle damage caused by excessive exercise cause cancer?

First understand the characteristics of skeletal muscle: The cells that make up skeletal muscle are called muscle fibers. They are multinucleated cells, and multinucleated cells do not divide or grow.

Principle of muscle growth: cells become larger and fuse with more cells.

The answer is no. After muscle injury, muscle stem cells divide and grow, then fuse into muscle fibers. Once fused, the cells lose the ability to divide and grow. Of course, a mutation may also occur during the first division, but cancer requires accumulation of multiple mutations, so this is not enough.

3.2.4. Radiation

There are two types of radiation: ionizing radiation and non-ionizing radiation.

1. Ionizing radiation: high energy; can directly damage DNA and cause gene mutations.

• Ultraviolet light in sunlight
• Naturally radioactive elements, widely present in rocks, soil, and air. Pay attention to natural stone used in home decoration.
• Medical radiation: X-rays, CT, and PET. MRI and ultrasound do not belong to this category.

2. Non-ionizing radiation: low energy, insufficient to damage DNA, and does not cause gene mutations.

3.3. How to Know Whether Cancer Was Caused by Internal or External Factors

Genetically analyze tumor cells, identify a mutational fingerprint, and compare it with databases. This may make it possible to determine which risk factor caused the mutation.

4. Early Symptoms of Cancer

1. A palpable hard lump, such as a lump in the breast or skin.
2. A wart or mole changes noticeably.
3. Persistent digestive abnormalities.
4. Persistent hoarseness, dry cough, or difficulty swallowing.
5. Abnormal menstruation, heavy bleeding, or bleeding outside menstruation.
6. Unexplained bleeding from the nose, ear, bladder, or intestine.
7. A wound that does not heal or swelling that does not go away.
8. Unexplained weight loss.

5. Cancer Prevention

5.1. Early Cancer Screening

Primary prevention: avoid cancer risk factors. Secondary prevention: physical-examination screening, meaning early detection, early diagnosis, and early treatment. Tertiary prevention: prevention after clinical diagnosis.

5.1.1. Cancer Screening Examinations

For the general population:

1. Female breast cancer
2. Female cervical cancer
3. Colorectal cancer

For high-risk populations:

1. Liver cancer
2. Stomach cancer
3. Lung cancer

Why are some examinations recommended only for high-risk groups? Because false negatives (disease exists but is not detected) and false positives (no disease but testing indicates disease) exist, causing a higher misdiagnosis rate in ordinary people.

5.1.2. Screening Methods

1. Imaging
   1. Ultrasound
   2. Magnetic resonance imaging (MRI)
   3. CT
   4. PET-CT
   5. Endoscopy
2. Tumor markers
   1. Alpha-fetoprotein (AFP)
   2. Prostate-specific antigen (PSA)
   3. Carcinoembryonic antigen (CEA)
   4. CA125
   5. CA199

5.2. Screening for Different Cancers

5.2.1. Lung Cancer

5.2.1.1. Who Is Suitable for Screening?

People who currently smoke or used to smoke and have a smoking index ≥400 (smoking index = cigarettes smoked per day × years of smoking). People with long-term exposure to harsh environments or occupational carcinogens. Patients with chronic obstructive pulmonary disease, diffuse pulmonary fibrosis, or previous lung diseases such as tuberculosis. Middle-aged and older adults aged ≥50. People with a family history of tumors, especially first-degree relatives with malignant tumors.

5.2.1.2. Screening Method

Low-dose CT.

Is Low-Dose Spiral CT Harmful to the Body? - Zhihu Is Annual Low-Dose Spiral CT for Physical Examination Scientific? How Should It Be Done? - Zhihu

Pulmonary nodules:

1. Solid nodules
2. Ground-glass nodules

• Pure ground-glass: solid component <5%
• Mixed ground-glass

Follow-up is recommended for diameter <5 mm.

5.2.2. Thyroid Cancer

Grades:

1. Papillary carcinoma. If diameter <1 cm, overtreatment is not recommended.
2. Follicular carcinoma
3. Anaplastic carcinoma
4. Medullary carcinoma

More than 90% of thyroid nodules are benign, and 5% are malignant. How to determine malignancy?

1. Clinical indicators Ultrasound: solid hypoechoic nodule with irregular boundary; serum indicator: very high TSH.
2. Needle pathology A fine needle is used to obtain a nodule sample for microscopic observation. There are six grades; grade 2 and below can be followed up.
3. Gene mutations For grades 3 and 4, genetic testing can be used for further assessment.

5.2.3. Nasopharyngeal Cancer

5.2.3.1. Who Is Suitable for Screening?

1. Family history of nasopharyngeal cancer
2. Living in a high-incidence area
3. Frequent exposure to carcinogenic factors
4. …

5.2.3.2. Screening Methods

1. Traditional methods
   1. Nasal endoscopy: check whether abnormal masses exist in the nasal cavity + biopsy.
   2. EB-virus-related antibody testing: blood test for antibodies.
2. EBV-DNA screening: two blood draws to test for EB virus.

5.2.4. Esophageal Cancer

5.2.4.1. Who Is Suitable for Screening?

People aged ≥45 who meet any of the following should be considered high risk and undergo regular esophageal-cancer screening: Come from a high-incidence area; Have upper gastrointestinal symptoms; Have a family history of esophageal cancer; Have precancerous esophageal disease or lesions; Have high-risk factors for esophageal cancer (smoking, heavy drinking, squamous-cell carcinoma of the head/neck or respiratory tract, preference for very hot or pickled foods, poor oral hygiene, etc.).

5.2.4.2. Screening Methods

Endoscopy. Biopsy pathology.

5.2.5. Stomach Cancer

5.2.5.1. Who Is Suitable for Screening?

People aged ≥45 who meet any of the following should be considered at high risk and undergo regular screening:

People from high-incidence regions; People infected with H. pylori; People with previous chronic atrophic gastritis, gastric ulcer, gastric polyps, postoperative remnant stomach, hypertrophic gastritis, pernicious anemia, and other precancerous gastric diseases; First-degree relatives of patients with stomach cancer; People with other stomach-cancer risk factors (such as high-salt intake, pickled foods, smoking, heavy drinking, etc.).

5.2.5.2. Screening Methods

1. Gastroscopy
2. H. pylori testing and serum-marker testing

5.2.6. Colorectal Cancer

5.2.6.1. Who Is Suitable for Screening?

People over age 50 who meet any of the following should be considered at high risk and undergo regular screening: A first-degree relative has a history of colorectal cancer (including non-hereditary and hereditary family histories). The person has a history of colorectal cancer. The person has a history of intestinal adenoma. The person has inflammatory bowel disease that has persisted for 8–10 years. The person’s fecal occult blood test is positive.

5.2.6.2. Screening Methods

1. Colonoscopy. If there are no abnormalities, once every 5–10 years.
2. Stool testing.

5.2.7. Liver Cancer

5.2.7.1. Who Is Suitable for Screening?

Men over 40 or women over 50 with chronic hepatitis B or C, or who are virus carriers. People with long-term heavy alcohol use and diabetes. People with cirrhosis. People with a family history of liver cancer.

5.2.7.2. Screening Methods

Liver ultrasound and serum alpha-fetoprotein (AFP).

5.2.8. Breast Cancer

5.2.8.1. Who Is Suitable for Screening?

Women over age 45 should receive regular breast-cancer screening. People with the following conditions should pay particular attention: Genetic testing shows that a first-degree relative within three generations carries a BRCA1/BRCA2 mutation. Relatives in the family have breast cancer, epithelial ovarian cancer, fallopian-tube cancer, or primary peritoneal cancer. Age at menarche ≤12. Age at menopause ≥55. Combined estrogen-progestin hormone-replacement therapy for at least six months. Previous atypical ductal or lobular hyperplasia or lobular carcinoma in situ.

5.2.8.2. Screening Methods

Mammography and ultrasound; MRI in special situations.

5.2.9. Cervical Cancer

5.2.9.1. Who Is Suitable for Screening?

Women who are sexually active should begin cervical cytology at age 21, once every three years. Beginning at age 30, high-risk HPV screening every 3–5 years. People who previously had or currently have genital HPV infection. Women with multiple sexual partners, or whose male partners have multiple sexual partners. Women who began sexual activity early (before age 18). Women whose male partner has a sexual partner with cervical cancer. People with HIV infection or other sexually transmitted diseases such as syphilis or gonorrhea. People receiving immunosuppressive treatment. People with long-term oral-contraceptive use, smoking, or drug addiction. People with a family history of cervical lesions.

5.2.9.2. Screening Methods

Primary prevention: high-risk HPV — receive HPV vaccination. Secondary prevention: cervical cytology and high-risk HPV screening.

5.3. Immunity

Normal immunity is enough; blindly trying to increase immunity is not recommended. How to judge whether immunity is normal? Look at the body’s ability to fight bacteria and viruses, such as whether colds are frequent or whether herpes appears at the corners of the mouth. How to maintain normal immunity?

1. Balanced diet
2. Moderate exercise
3. Avoid antibiotic abuse
4. Develop and maintain good lifestyle habits

7. References

• Chinese Anti-Cancer Association Popular Science Guide to Cancer Screening
• Cancer Incidence in Guangdong Province - Guangdong Provincial Center for Disease Control and Prevention
• Cancer: Defense (Douban)