Cancer: A Brief Overview
Cancer: A Brief Overview

Cancer: A Brief Overview

Lead Author(s): Virginia Githiri

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Brief overview of cancer and related factors including, but not limited to, cancer descriptions, cancer epidemiology, culture and cancer, and ethics and cancer.

Chapter 1: What is Cancer

Cancer is pervasive in our world. Due to the widespread nature of this disease, most of us know at least one person, impacted by cancer in some way. The development of cancer may be understood by the examination of two models - hierarchical and stochastic. Also, cancer severity is understood, as related to the particular stage of the disease. There are many unavoidable causes of cancer including our genetics and the environment. However, there are even more factors, primarily related to personal lifestyle and behavior, which we can control, to decrease our risk of developing this, often fatal, disease. 

Part 1: Cancer, a Description

Cancer is a term used to represent more than 200 related diseases in which cells divide uncontrollably. Cancer is also an invasive disease indicated by the spreading of diseased cells to other parts of the body through the lymphiod system.

Bone Cancer Cell [1]

The human body is comprised of trillions of cells. In a normal, healthy cell division process, when old cells die, new cells emerge. Cancer disrupts the cell division process such that old cells remain and new cells form unnecessarily, creating tumors. Important note, some cancers, like leukemia, do not form tumors, but, exist in the blood.

Part 1.1: Tumors:

There are two types of tumors, benign and malignant. Benign tumors are non-cancerous, yet, can grow very large. However, these tumors will not spread and are non-invasive. Furthermore, if successfully removed via surgery, benign tumors will not grow back. As an exception, if a benign tumor is found pressing on the brain, or other vital organs, the result may be fatal. 

Cancerous growths are known as malignant tumors. Malignant tumors are invasive and have the ability to reproduce uncontrollably. Another characteristic of malignant tumors is their ability to metastasize, or spread to other parts of the body.  

Benign Tumors

Malignant Tumors

Often capsulated (protective sac around tumor)


Slow growing

Fast growing



Metastasis sites for common cancers [2]
Benign VS Malignant

Click on the target indicating the correct answer. Malignant tumors remain the size of a pea and never spread to other organs.

Part 1.2: Cancer Development Models

Two models are commonly used to describe how a cancer develops. The first cancer development model is called the  hierarchical model, (also known as the the cancer stem cell (CSC) model). This model indicates that:

  1. Cancer cells within a tumor fall into distinct subpopulations with differing functional abilities and behaviors. 
  2. Only cancer stem cells can initiate new tumors.
  3. Cancer stem cells can produce more cells like themselves, or differentiate to form different cell types. 

The second model, the Stochastic Model also known as Knudson’s random “two hit” model. This model suggests that:

  1. Each cancer cell within a tumor are (biologically) equivalent. 
  2. The cells operate differently due to stochastic factors, which affect the tumor's microenvironment.
  3. All cancer cells within a tumor have equal abilities in the intiation of new tumors. 

Hierarchical and stochastic models of tumour cell heterogeneity [3]

Part 2: Cancer Staging

Cancer is often described by the stage. In general, stage includes the size of the tumor or the extent of the cancer. It is important to note that stage varies per each type of cancer. Utimately, understanding cancer stage is critical for providing better accuracy with respect to diagnosis, treatment, and survival rates. 

Part 2.1: TNM (Tumor, Number, Metastasis) Staging

Cancer is often described by the TNM staging system. "T" relates to the extent and size of the primary tumor. "N" is related to the number of lymph nodes with cancer and "M" confirms metastasis. Digits are added after each letter, T, N, and M, to further describe the cancer.

TNM Staging: Primary Tumor (T) [4]
TMN Staging: Regional Lymph Nodes (N) [5]
TMN Staging: Metastasis (M) [6]
TNM (tumor, number, metastasis) staging

Based upon the following staging, T1M0N0, select the best description of the cancer.


Small tumor, cancer in lymph nodes, and cancer has metastasized to other parts of the body.


Small tumor, no cancer in lymph nodes, and cancer has metastasized to other parts of the body.


Large tumor, no cancer in lymph nodes, and cancer has not metastasized to other parts of the body.


Large tumor, no cancer in lymph nodes, and cancer has metastasized to other parts of the body.

Part 2.2: Number Staging

A numbering system may also be used to stage cancer. Numbers range from 0 to IV. Stage 0 indicates that the abnormal cells are not cancerous. Stages I - III indicates the fact that cancer is present, and has likely spread to other tissues. Cancer which has metastisized to other parts of the body is stage IV.  

Part 2.3: Location Staginig

Finally, cancer may be staged by using terms to describe the location of the cancer, as indicated below.

cancer spreading stages.jpg
Cancer Spreading [7]

Part 3: Cancer Risk Factors

Cancer is a multi-factoral disease because there are a variety of factors, which have been identified in contributing to the development of the disease. The suspected cancer risk factors are numerous and range from tobacco smoke to genetics. It may be difficult to link a singular factor to a particular type of cancer. Nonetheless, it is important to distinguish the difference between the factors to which we have control (modifiable), compared to those that we have no control (non-modifiable).  

Part 3.1: Modifiable Cancer Risk Factors

Dietary Behaviors

There exist some evidence that dietary behaviors may be linked to increasing or decreasing cancer risk. It is recommended, when possible, certain dietary practices be observed including: 

  • minimal consumption of red meat (including beef, pork and lamb)
  • smaller amounts of processed meats like sausage, bacon, and lunch meat.
  • increase intake of high-fiber foods including fruits, vegetables, and whole grains, beans and legumes.
Colours of Health [8]

Physical Activity and Obesity

Research provides support for the consmption of physical activity as a potential method to decrease cancer risk. The evidence for this fact is strongest for colon, breast, and endometrial cancer. Obesity has also been linked to an increased risk for esophagus, gastric, colorectal, liver, gallbladder, pancreas, breast (postmenopausal), corpus uteri, ovary, kidney: renal-cell, meningioma, thyroid, and multiple myeloma cancers. 

Cigarette Smoking

The third factor, is cigarette smoking. Not only has smoking been identified as the single most significant cause of preventable death, but has also been linked to multiple cancers as displayed below.

word cloud smoking and cancer.png
Cancers Linked to Smoking [9]

Consequently, 1 in 3 cancer deaths are linked to smoking. 

Part 3.2: Non-Modifiable Cancer Risk Factors

An individual may have reasonable dietary habits, participate in physical activity, abstain from tobacco smoke and still develop cancer as per factors they cannot control. Such non-modifiable risk factors include age, envirorment, and genetics. 

Aging is a natural process for all living organisms. And, cancer can occur at any age. However, more than 70% of cancers are newly diagnosed in individuals aged 55 and over. Therefore, age, is the most significant, non-modifiable risk factor for cancer. 

rate of cancer by age 2015.jpg
Rate of New Cancers By Age Group, All Races, Both Sexes, United States, 2015 [10]
Cancer and Risk Factors

What is the most significant non-modifiable cancer risk factor?

Part 4: Cancer Categories

Most cancers are named for the organ or type of cell in which they start. The seven primary categories of cancer are carcinoma, sarcoma, leukemia, lymphoma, multiple myeloma, melanoma, and central nervous system tumors. The following section includes a brief description for each cancer category. 

Part 4.1: Carcinomas

Carcinomas, are the most common type of cancer and begin in the epithelium. There are four varieties of carcinomas. Basal cell carcinoma is the first variety and causes 8 out of 10 skin cancers. This type of skin cancer is typically found on the head and neck, as these areas are commonly exposed to the sun's ultraviolet (UV) rays. The second type of skin cancer, adenocarcinoma, forms in glandular tissues and include colon, prostate, and breast cancer. Squamous cell is the next carcinoma variety and also occur on sun-exposed areas of the body including lips, neck, ears, back of the hands, and face. While a rare occurance, squamous cell carcinoma may develop in the stomach, kidneys, bladder, and lungs and/or skin of the genital area. The fourth variety is transitional cell carcinoma. This type of carcinoma may cause bladder, ureter and/or kidney cancer .  

Basal cell carcinoma [11]

Part 4.2: Sarcomas

Sarcomas are fairly rare and are seen most commonly in children. These tumors start in the soft tissues and bone and include blood vessels, tendons, ligaments, fat, lymph vessels, and muscle. While sarcomoas are commonly found in the arms, legs, chest, and abdomen, they may be found in nearly any part of the body.   

Part 4.3: Leukemias

Cancers that begin in the blood-forming tissues, such as bone marrow, are called leukemias. These cancers are commonly diagnosed in persons age 0 - 14. Leukemias do not form solid tumors but develop due to the build up of abnormal white blood cells into the blood and bone marrow. This process drives out normal blood cells and impedes the body's ability to fight infections, get oxygen to its tissues, or control bleeding. 

Leukemia [12]

Part 4.4: Lymphoma

Lymphoma affects the immune system disease-fighting T & B lymphocytes. Two primary types of lymphoma include Hodgkin lymphoma and Non-Hodgkin lymphoma. Hodgkin lymphoma may be found anywhere, in the human body, where lymph tissues are found. Most often, under the arms, chest, or neck. While not common, Hodgkin lymphoma may expand to the bone marrow, or other parts of the body, in late stage of the disease. 

Lymphoma [13]

Part 4.5: Multiple Myeloma

Overgrown plasma cells that become cancerous, is a perfect environment for multiple myeloma. Low blood count is a primary symptom of this type of cancer and may be indicated by anemia (low red blood cells), leukopenia (low normal white blood cells), and/or thrombocytopenia (low blood platelets).    

Part 4.6: Melanoma

Melanoma skin cancer is rare, yet deadly. It begins in the melanocytes. Often found on the chest, back, legs, face and neck, melanoma may spread to other parts of the body if left untreated. 

Melanoma in adult woman [14]

Part 4.7: Central Nervous System Tumors 

Central nervous system (CNS) tumors begin in the tissues of the brain and/or spinal cord. Not all CNS tumors are malignant. However, even the benign variety may still cause significant morbidity and impairment and should be treated. Sadly, malignant CNS tumors carry a high mortality rate, regardless of the time of diagnosis. The most common type of brain tumor is a metastatic brain tumor. 

malignant brain tumor.jpg
PET scan showing malignant brain tumor [15]

Cancer and Children

Which of these cancer(s) is most commonly diagnosed in children?












Answers B & C are correct


All of the above

Part 5: Common Cancer Types: By The Numbers

As previously mentioned in Part 1 of this chapter, the term cancer represents more than 200 diseases. The five most common cancers are: breast, lung, prostate, colorectal (colon & rectal), and melanoma. The table below includes the 2018 cancer estimates for new cases and deaths. Chapters 3- 7, will include a detailed discussion of each type of cancer, as indicated in the table below. 

Cancer Type

Estimated New Cases

Estimated Deaths


266,120 (female)
2,550 (male)

40,920 (female)
480 (male)







Colorectal (colon & rectal)






Cancer Estimates

Based upon the 2018 data provided in chapter 1, which type of cancer projects a greater than 50% death rate estimate, when compared to estimated new cases of cancer?








Colorectal (Colon & Rectal)



Part 6: Cancer Screening

High-risk individuals may benefit from cancer screening. Screening recommendations and methods vary per the type of cancer in question. It is important to note, not all cancers have screening recommendations. Nonetheless, we will review specific screening protocol in subsequent chapters of this textbook. While screening may help clinicians to find disease early, there are no guarantees to decrease the risk of death.  

If a cancer screening procedure has been recommend, it is believed that the benefits to the patient, exceed the costs. Even so, a few issues should be taken into consideration when considering a decision to be screened. 

Screening may be uncomfortable or painful for the patient. 

Some screening procedures are rather invasive, requiring surgery and potential recovery time. 

Unecessry screening may lead to overdiagnosis of disease. Even if the patient has cancer, they may undergo an aggressive treatment, potentially causing other physical symptoms. The subsequent outcomes, may not had occured had they not undergone screening.

Finally, screening may have incorrect outcomes including false-positive, false-negative, or indeterminate significance. These outcomes may be further understood by examination of the chart below.





Screening results indicate that cancer is not present when the patient actually has cancer. 

The patient may have a false sense of assurance and delay necessary treatment. 


 Screening results indicate that cancer may be present when the patient is cancer-free. 

The patient may undergo emotional stress and feel unnecessarily anxious. They may also undergo additional unnecessary testing, cancer reducing medical procedures, and/or take medications that they do not need, as a result.  

Indeterminante significance

Screening results can not determine whether or not the patient has cancer. 

The patient may become frustrated and discouraged, especially if they were eager to have a confirmed outcome. 

Part 7: Cancer Treatment

The ultimate goal of cancer treatment is to eliminate the disease. However, a complete cure is not always possible. Nonetheless, recommended treatment options depend upon a variety of factors including the patient's health status, the type of cancer, the size and location of the tumor(s), and metastasis of the disease. Cancer treatment for specific types of cancer will be discussed in subsequent chapters of this textbook. 

Chapter 1 critique (completely anonymous and optional)

What did you enjoy most about chapter 1?

What was your least favorite thing about chapter 1?

Other comments?

Key Terms

Cell -  In biology, the smallest unit that can live on its own and that makes up all living organisms and the tissues of the body. A cell has three main parts: the cell membrane, the nucleus, and the cytoplasm. The cell membrane surrounds the cell and controls the substances that go into and out of the cell. The nucleus is a structure inside the cell that contains the nucleolus and most of the cell’s DNA. It is also where most RNA is made. The cytoplasm is the fluid inside the cell. It contains other tiny cell parts that have specific functions, including the Golgi complex, the mitochondria, and the endoplasmic reticulum. The cytoplasm is where most chemical reactions take place and most proteins get made. The human body has more than 30 trillion cells. 

Metastatic -  Having to do with metastasis, which is the spread of cancer from the primary site (place where it started) to other places in the body. 

Multiple myeloma -  A type of cancer that begins in plasma cells (white blood cells that produce antibodies). Also called Kahler disease, myelomatosis, and plasma cell myeloma. 

Screening -  Checking for disease when there are no symptoms. Since screening may find diseases at an early stage, there may be a better chance of curing the disease. Examples of cancer screening tests are the mammogram (for breast cancer), colonoscopy (for colon cancer), and the Pap test and HPV tests (for cervical cancer). Screening can also include doing a genetic test to check for a person’s risk of developing an inherited disease. 

TNM Staging -  A system to describe the amount and spread of cancer in a patient’s body, using TNM. T describes the size of the tumor and any spread of cancer into nearby tissue; N describes spread of cancer to nearby lymph nodes; and M describes metastasis (spread of cancer to other parts of the body). This system was created and is updated by the American Joint Committee on Cancer (AJCC) and the International Union Against Cancer (UICC). The TNM staging system is used to describe most types of cancer. Also called AJCC staging system.


Image Credits

[1] Image  By  Dylan Burnette and Jennifer Lippincott-Schwartz, NIH courtesy of National Cancer Institute. Image under public domain. 

[2] Image By Mikael Häggström, [CC0], via Wikimedia Commons. Image under public domain. 

[3]  Image By WassermanLab, CC BY-SA 4.0, from Wikimedia Commons. Image under public domain. 

[4] Staging: Primary Tumor created by Virginia Githiri. Imaged used with personal permission. 

[5] Staging: Regional Lymph Nodes created by Virginia Githiri. Image used with personal permission. 

[6] Staging: Distant Metastasis created by Virginia Githiri. Image used with personal permission. 

[7] Cancer Spreading by Virginia Githiri. Image used with personal permission. 

[8] Image By Alex Proimos from Sydney, Australia - Colours of Health, CC BY 2.0. Image under public domain. 

[9] Word cloud created by Virginia Githiri. Image used with personal permission. 

[10] Image  by U.S. Cancer Statistics Working Group. U.S. Cancer Statistics Data Visualizations Tool, based on November 2017 submission data (1999-2015): U.S. Department of Health and Human Services, Centers for Disease Control and Prevention and National Cancer Institute;, June 2018. 

[11] Image By Bin im Garten, CC BY-SA 3.0, via Wikimedia Commons. Image under public domain. 

[12] Image By Manu Sharma,, CC BY-SA 4.0, via Wikimedia Commons. Image under public domain. 

[13] Image from  Dr. Lance Liotta Laboratory, by Unknown photographer, courtesy of National Cancer Institute, Image under public domain. 

[14] Image by  Lydia Kibiuk (Illustrator), courtesy of National Cancer Institue. Image under public domain. 

[15] Image By Simone Trovato Monastra, CC BY-SA 4.0, from Wikimedia Commons. Image under public domain. 


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Referring to lymphocytes, a type of white blood cell. Also refers to tissue in which lymphocytes develop.
Lymphoid system
Referring to lymphocytes, a type of white blood cell. Also refers to tissue in which lymphocytes develop.
The extent of a cancer in the body. Staging is usually based on the size of the tumor, whether lymph nodes contain cancer, and whether the cancer has spread from the original site to other parts of the body.
Body Mass Index (BMI) is a person's weight in kilograms divided by the square of height in meters. A high BMI can be an indicator of high body fatness.
Body Mass Index (BMI) is a person's weight in kilograms divided by the square of height in meters. A high BMI can be an indicator of high body fatness.
A thin layer of tissue that covers organs, glands, and other structures within the body.
T Lymphocytes
A type of white blood cell. T lymphocytes are part of the immune system and develop from stem cells in the bone marrow. They help protect the body from infection and may help fight cancer. Also called T cell and thymocyte.
B Lymphocyte
A type of white blood cell that makes antibodies. B lymphocytes are part of the immune system and develop from stem cells in the bone marrow. Also called B cell.
A type of cancer that begins in plasma cells (white blood cells that produce antibodies). Also called Kahler disease, myelomatosis, and plasma cell myeloma.
A cell in the skin and eyes that produces and contains the pigment called melanin.
Having to do with metastasis, which is the spread of cancer from the primary site (place where it started) to other places in the body.