Cancer Types

Introduction to Cancer Types

Cancer is not a single disease but a collection of diseases characterized by the uncontrolled growth and spread of abnormal cells. Why do you think cancers vary so much in their behavior? The answer lies in their origins—cancers are classified based on the type of cell or tissue they start from. This classification is critical for understanding the disease, guiding diagnosis, and tailoring treatments. The five primary categories of cancer are:

• Carcinoma: These cancers arise from epithelial cells, which line the body’s internal and external surfaces, such as the skin, lungs, or breast tissue. Carcinomas are the most common, making up 80-90% of all cancer cases. Examples include breast, lung, and colorectal cancers.
• Sarcoma: Originating from connective tissues like bone, cartilage, fat, or muscle, sarcomas are rare, accounting for less than 1% of cancers. Examples include osteosarcoma (bone) and chondrosarcoma (cartilage).
• Lymphoma: These cancers begin in the lymphatic system, part of the immune system. They are divided into Hodgkin’s lymphoma and non-Hodgkin’s lymphoma, comprising about 5% of cancers.
• Leukemia: Known as blood cancers, leukemias start in the bone marrow and affect blood cells, particularly white blood cells. They account for about 3% of cancers and are the most common cancer in children.
• Myeloma: This cancer affects plasma cells in the bone marrow, with multiple myeloma being the most common form, representing about 2% of cancers.

Additionally, cancers like brain and spinal cord tumors form another category, though they are less common, making up about 3% of cases. Why do you think classifying cancers by their cell type is more useful than just naming them by the organ they affect? Could it reveal more about how they grow or respond to treatment?

Number of Cancer Types

How many types of cancer do you think exist? The National Cancer Institute (NCI) states there are over 100 distinct types of cancer, typically named for the organ or tissue where they originate, such as lung or breast cancer, or the cell type, like squamous cell carcinoma (National Cancer Institute, 2023). However, Cancer Research UK suggests there may be over 200 types when including subtypes, such as different forms of breast or lung cancer (Cancer Research UK, 2023). Why might these estimates differ? Could it be due to how subtypes are counted or because new cancers are identified over time? The exact number is fluid as research advances and classifications evolve, but over 100 is a widely accepted figure for distinct cancer types.

This diversity underscores the complexity of cancer, requiring tailored approaches for diagnosis and treatment. What challenges might arise from having so many cancer types? Could it affect how researchers develop new therapies?

Cancer Death Rates in Hong Kong

In Hong Kong, cancer is a leading cause of death, claiming 14,717 lives in 2022, which accounted for about one-fourth of all deaths (Hong Kong Cancer Registry, 2025). What factors might contribute to such a high cancer burden? The top five causes of cancer deaths in 2022 were:

These five cancers accounted for 50.7% of all cancer deaths in Hong Kong (Hong Kong Cancer Registry, 2025). Why do you think lung cancer leads by such a large margin? Could lifestyle factors like smoking or environmental factors like air pollution be involved? The data also shows that 84% of cancer deaths occurred in individuals aged 60 or older, with a median age at death of 72 years for both men and women. How might an aging population influence cancer death rates?

Trends in Cancer Mortality

Over the past three decades, age-standardized mortality rates for cancer in Hong Kong have been declining, likely due to advancements in screening, early detection, and treatments (Hong Kong Cancer Registry, 2025). However, the total number of deaths remains high due to an aging population. Why might an aging population increase cancer deaths even if mortality rates are declining? Could it be related to the higher incidence of cancer in older age groups?

Detailed Information on Each Cancer Category

Let’s explore each cancer category to understand their characteristics and significance. What makes each type unique, and how might this affect treatment approaches?

1. Carcinoma

• Description: Carcinomas originate in epithelial cells, which form the lining of organs, glands, and the skin. They are the most common cancers, accounting for 80-90% of cases.
• Examples: Breast, lung, prostate, colorectal, and skin cancers (e.g., basal cell carcinoma, squamous cell carcinoma).
• Characteristics: Carcinomas often grow slowly and can spread to nearby tissues or distant organs via the lymphatic system or bloodstream. Subtypes include:
  • Adenocarcinoma: Starts in glandular cells (e.g., breast, lung).
  • Squamous Cell Carcinoma: Begins in squamous cells (e.g., skin, esophagus).
  • Basal Cell Carcinoma: Common in the skin, rarely metastatic.
• Significance in Hong Kong: Lung, colorectal, and breast cancers, all carcinomas, are among the top causes of cancer death, highlighting their public health impact.

Why do you think carcinomas are so common? Could it be because epithelial cells are constantly dividing, making them more prone to mutations?

2. Sarcoma

• Description: Sarcomas arise from connective tissues, such as bone, cartilage, fat, muscle, or blood vessels.
• Examples: Osteosarcoma (bone), chondrosarcoma (cartilage), liposarcoma (fat), rhabdomyosarcoma (muscle).
• Characteristics: Sarcomas are rare, making up less than 1% of cancers, but can be aggressive, often requiring surgery.
• Significance in Hong Kong: Sarcomas are not among the top causes of cancer death but are significant due to their potential severity, especially in younger patients.

What challenges might doctors face in treating sarcomas? Could their rarity make them harder to diagnose or treat?

3. Lymphoma

• Description: Lymphomas start in the lymphatic system, which helps fight infections.
• Types:
  • Hodgkin’s Lymphoma: Identified by Reed-Sternberg cells.
  • Non-Hodgkin’s Lymphoma: A diverse group with many subtypes.
• Characteristics: Lymphomas can occur at any age but are more common in older adults. They are often treatable with chemotherapy or immunotherapy.
• Prevalence: Accounts for about 5% of cancers.
• Significance in Hong Kong: While not a leading cause of death, lymphomas are notable for their treatability when detected early.

Why might lymphomas be more treatable than other cancers? Could it be related to their origin in the immune system?

4. Leukemia

• Description: Leukemias are cancers of the blood and bone marrow, characterized by excessive abnormal white blood cells.
• Types:
  • Acute Lymphocytic Leukemia (ALL): Common in children.
  • Acute Myeloid Leukemia (AML): Common in adults.
  • Chronic Lymphocytic Leukemia (CLL): Slow-growing, common in older adults.
  • Chronic Myeloid Leukemia (CML): Treatable with targeted therapies.
• Characteristics: Leukemias can be acute (fast-growing) or chronic (slow-growing), affecting the body’s ability to fight infections.
• Prevalence: Accounts for about 3% of cancers, most common in children.
• Significance in Hong Kong: Leukemia is less common as a cause of death but is critical due to its impact on younger populations.

How might leukemia’s effect on blood cells complicate treatment? Could it require different approaches than solid tumors?

5. Myeloma

• Description: Myeloma, particularly multiple myeloma, affects plasma cells in the bone marrow, which produce antibodies.
• Characteristics: It can cause bone pain, fractures, anemia, and kidney problems, often detected through abnormal protein levels in blood.
• Prevalence: Accounts for about 2% of cancers.
• Significance in Hong Kong: Myeloma is not a leading cause of death but impacts quality of life due to its chronic nature.

Why might myeloma be harder to detect early? Could its symptoms be mistaken for other conditions?

Specific Cancers Leading to Death in Hong Kong

Let’s examine the top five cancers causing deaths in Hong Kong in 2022. What makes these cancers so deadly, and how might prevention strategies help?

• Lung Cancer:
  • Deaths in 2022: 3,782 (25.7%)
  • Risk Factors: Smoking, air pollution, occupational exposures.
  • Significance: Lung cancer’s high mortality is due to late-stage diagnosis and aggressive behavior. Despite declining smoking rates, it remains the top killer. Why do you think early detection is so challenging for lung cancer?
• Colorectal Cancer:
  • Deaths in 2022: 2,270 (15.4%)
  • Risk Factors: Diet (low fiber, high red meat), obesity, family history.
  • Significance: Screening, like colonoscopies, can significantly reduce mortality by detecting precancerous polyps. How might public awareness campaigns improve screening rates?
• Liver Cancer:
  • Deaths in 2022: 1,412 (9.6%)
  • Risk Factors: Chronic hepatitis B and C, cirrhosis, alcohol abuse.
  • Significance: Hong Kong’s high prevalence of hepatitis B contributes to liver cancer’s impact. Could vaccination programs help reduce this burden?
• Pancreatic Cancer:
  • Deaths in 2022: 920 (6.3%)
  • Risk Factors: Smoking, obesity, family history.
  • Significance: Often diagnosed late, making treatment difficult. Why might pancreatic cancer be so hard to detect early?
• Breast Cancer:
  • Deaths in 2022: 804 (5.5%)
  • Risk Factors: Age, family history, genetic mutations (e.g., BRCA1/2).
  • Significance: Early detection through mammography improves survival. How could increased screening access reduce deaths?

Conclusion

Cancer’s complexity is evident in its classification, with over 100 types grouped into categories like carcinoma, sarcoma, leukemia, lymphoma, and myeloma. Each category has unique characteristics that guide treatment and prognosis. In Hong Kong, cancer remains a major health challenge, with 14,717 deaths in 2022, led by lung, colorectal, liver, pancreatic, and breast cancers. These statistics highlight the need for targeted prevention, early detection, and advanced treatments. Why do you think some cancers are more deadly than others? Could lifestyle changes, screening, or new therapies make a difference? Continued research and public health efforts are essential to reducing cancer’s impact in Hong Kong and globally.

Citations

• National Cancer Institute. (2023). A to Z List of Cancer Types. Retrieved from https://www.cancer.gov/types
• Cancer Research UK. (2023). Types of Cancer. Retrieved from https://www.cancerresearchuk.org/about-cancer/what-is-cancer/how-cancer-starts/types-of-cancer
• Hong Kong Cancer Registry. (2025). Overview of Cancer Statistics in Hong Kong. Retrieved from https://www.cancer.gov.hk/en/hong_kong_cancer/overview_of_cancer_statistics_in_hong_kong.html