Learning Objectives
By the end of this section, you will be able to:
- Discuss the pathophysiology, risk factors, and clinical manifestations of cancer
- Differentiate the major types of cancer
There are more than 200 types of cancer, all characterized by uncontrolled and abnormal cell growth (Cancer Research UK, 2023). This results in cells that are poorly differentiated and unable to perform their function within the body. The primary effect of cancer is the disruption of typical body functions. The goal of treatment is to interrupt the uncontrolled growth of abnormal cells to manage the disease and restore normal function.
Cancer is thought to be caused by three main factors (National Cancer Institute [NCI], n.d.; Nationwide Children’s, 2023; Stanford Medicine, n.d.):
- Systemic issues—often due to immune dysfunction or chronic inflammation
- Environmental exposures—chronically poor diet, pollution, certain viruses
- Genetic determinants—inherited or acquired
These factors may intersect to increase the risk of cancer development.
Pathophysiology
A normal cell has deoxyribonucleic acid (DNA), which gives the cell correct instructions about its work in the body and when the cell should die. The process of normal cell death as part of a controlled and normal process is called apoptosis. To allow cancer to develop, a mutation must be initiated. Often, the initiation of a mutation is caused by repeated or prolonged insults to the cell’s DNA, such as consistent skin tanning or repeated chemical exposure at work. In medical terms, an insult is the cause of some kind of physical injury. The DNA insult initiates a mutation and apoptosis is avoided. This is the beginning of most cancer types.
Smoking is a classic example of an insult as cigarettes contain many known carcinogens. carcinogen is a cancer-causing substance. The cell easily repairs damage from early exposure, but errors in the DNA and cell instructions become increasingly likely to occur. Recall that DNA contains the instructions needed for development, survival, and reproduction (National Human Genome Research Institute, 2020). If the DNA and its instructions are altered, the cells produced are not fully functional. Lung cells are damaged from inhaled carcinogens and the DNA instructions for the new lung cells are also damaged. This cycle continues, with each replication of lung cells exhibiting more damage and less expected functionality as part of the lung tissue. Eventually, this process creates cancerous cells. Then lung cells cannot serve the purpose of exchanging gases. Early symptoms of the cellular and tissue changes in lung cells include coughing or a change in breathing. The symptoms associated with disrupted function are usually what causes an individual to seek care.
The process the body uses to search for, identify, and destroy foreign pathogens and cancerous cells using cytotoxic T lymphocytes (or T cells), activated macrophages, and natural killer cells is called immunosurveillance (Figure 31.2). When enough cancerous cells have evaded immunosurveillance, a malignant, or cancerous, growth begins.
Tumors are malignant or benign. A malignant growth is cancerous, grows uncontrollably, and invades other areas of the body. They represent a threat to life, regardless of which part of the body is affected. A benign tumor grows slowly and does not spread. Whether they are a threat to life depends on their location and size. A benign tumor can grow and cause dysfunction by
- displacing tissues,
- pressing on nerves or vessels, or
- causing organ damage.
The hallmarks of a malignant growth are as follows:
- metastasis: cancerous cells can spread, usually via the bloodstream or lymphatic system (Figure 31.3)
- angiogenesis: cancerous cells can form their own network of blood vessels to obtain needed nutrients and oxygen and to allow tumor cells to leave the primary tumor site and metastasize to other parts of the body
- proliferation: cancerous cells have the ability to sustain their own growth without external stimuli
- evasion: cancerous cells can avoid growth suppression and apoptosis, or cell death
- immortality: cancerous cells have unlimited replication potential
Link to Learning
Read about Henrietta Lacks and her immortal cells to see uncontrolled cell growth at work in medical research. Consider reading more about Henrietta Lacks and unethical research practices in The Immortal Life of Henrietta Lacks by Rebecca Skloot.
Risk Factors
Not all cancers can be attributed to known risk factors, and scientific researchers and clinicians may not be able to determine their origin. However, this does not mean there are not any risks that might be controlled or modified. Many cancers do have risk factors that can be managed.
Preventable causes of mutations that may lead to cancer include the following:
- smoking
- dietary fat intake
- alcohol consumption
- low fiber intake
- low intake of micronutrients (beta-carotene, vitamin A, vitamin C, vitamin E)
- passive smoking (second-hand exposure)
- prolonged exposure to sex hormones (early menarche, exogenous hormones)
- occupational exposures (asbestos, benzene, ionizing radiation, lead, sun exposure)
- viruses (hepatitis B, human papillomavirus [HPV], Epstein-Barr virus, human immunodeficiency virus [HIV])
An imbalanced diet is linked to cancer development (NCI, 2023a). Often, imbalanced diets contain too little anti-inflammatory food and too much pro-inflammatory food. Naturally protective, anti-inflammatory compounds are found in foods such as blueberries, apples, olive oil, kale, almonds, and salmon. Conversely, chronic inflammation is triggered by red meat (due to its chemical digestive by-products) and processed foods, which contain preservatives, dyes, and other substances that are not natural to the human body.
The use of tobacco, in any form, and alcohol are linked to multiple types of cancer (Figure 31.4). Inactivity for long periods of time and obesity are also attributable to multiple types of cancer. Many of these risks will coexist for an individual, compounding the risk of cancer development.
Other factors that may initiate cell dysregulation include exposure to industrial chemicals or environmental pollution, prolonged time in the sun, infections such as hepatitis B and C or HPV, and hormone replacement or dysfunction.
Nonmodifiable causes of mutations that may lead to cancer include the following:
- age
- biological sex
- ethnicity
- genetic predisposition
Age is a risk factor that cannot be modified, but screenings for cancer are adjusted according to age and the established risk. With each year of age, mutations accumulate in DNA of cells. As they accumulate, it is more likely that a DNA change will occur that the body cannot control.
Genetics plays a significant role in cancer development. Genetic factors can be considered innate (being present during fetal development) or acquired (developed over time).
Innate Genetic Factors
Mutations that are inherited involve an innate genetic factor. This should be suspected if an individual has, or had, a close relative who developed cancer at a young age. For example, a patient may indicate that they have a first-degree relative who was diagnosed with breast cancer or colon cancer when the relative was in their 30s or 40s. The nurse recognizes the familial disposition of these specific cancer types and makes recommendations based on the appropriate high-risk guidelines.
A tumor suppressor gene normally regulates cell replication (Figure 31.5). Normally, these tumor suppressor genes produce tumor suppressor proteins that prevent cancer development by stabilizing the cell’s genetic material. During the cell repair process, these genes provide instructions to prevent the replication of insulted or damaged cells, leading to the death of the damaged cell. When these genes are inactivated (or turned off), they cannot suppress cell proliferation or tumor growth. This loss of function allows cancer cells to grow even though their DNA is damaged and should trigger apoptosis in the cell cycle.
Well-known examples of innate genetic factors are the BRCA1 and BRCA2 genes (Figure 31.6). When these genes are mutated or inactive, the risk for development of breast, ovarian, prostate, and pancreatic cancer increases. Mutations in the BRCA1 and BRCA2 genes are inherited. If an individual knows the mutation is in their family or has been personally tested for its presence, they can control risk factors, increase screening vigilance, or request preventive treatment, such as surgical removal of the organ or tissue.
Lynch syndrome, also known as hereditary nonpolyposis colorectal cancer, is an inherited condition characterized by mutations in genes responsible for repairing DNA replication errors. This syndrome significantly increases the risk of developing colorectal and endometrial cancers. In individuals with Down syndrome, the presence of an extra chromosome 21 elevates the risk of leukemia, testicular cancer, and solid tumors. This increased risk is thought to be related to genetic factors that affect cell growth and division.
Acquired Genetic Factors
Changes that often develop from exposure to risk factors, such as unhealthy daily habits, exposure to toxins, or hormone disruptions, are an acquired genetic factor. A somatic mutation is one that occurs over an individual’s lifetime—insults accumulated from actions such as smoking or random failure of the DNA to replicate correctly while reproducing cells. Whenever cells are damaged, they move through the cell cycle faster than usual to try to repair the damage. This faster pace increases the chance of random replication errors. Genomic instability refers to the mutations that occur in the cell's DNA repair and replication systems. This instability leads to more changes in the genetic material and increases the likelihood of replication errors. A gene that becomes cancerous when activated or turned on is called an oncogene. Acquired mutations trigger oncogenes to be active and promote cell growth and division. Overactive cell replication mechanism signaling produces a pro-cancer effect, encouraging cancer cells to grow. Examples of oncogenes include the following:
- HER2 (certain breast cancers)
- KRAS (colorectal or pancreatic cancer)
- ABL1 (chronic myeloid leukemia)
- EGFR (lung cancer and glioblastoma)
Each of these oncogenes has its own path for causing cancer: improperly promoting cell division, activating cell growth pathways continuously, increasing cell proliferation, inhibiting cell death, or producing substances that drive uncontrolled cell growth. Identifying oncogenes and tumor suppressor genes gives clinicians new ways to predict the likelihood of a cancer developing or being present.
Clinical Manifestations
Signs and symptoms are unique to each type of cancer. There are a few manifestations that are common to most cancers; however, they are nonspecific and often lead to delays in diagnosis. Fatigue is the most frequently reported manifestation, affecting as many as 91 percent of patients (NCI, 2024b). The fatigue is persistent, not relieved by rest, and not proportional to the energy that the patient expended. This can be attributed to the systemic response to the cancer, its impact on normal physiological functions, or other cancer-related physiological changes such as sleep disturbances, nausea, infection, anorexia, dyspnea, or anemia.
Weight loss is a common manifestation of cancer. Unexplained weight loss, a common question on hospital admission paperwork, is sudden and unintentional. An example would be a 5 percent weight loss over the past three months. The reasons for this weight loss often align with the type of cancer and not just the body’s work in fighting the cancer.
Changes that are unique to a given cancer type and require diagnostic investigation include the following:
- Solid and site-specific tumors, usually have symptoms of
- pain,
- lumps,
- swelling,
- skin changes,
- difficulty breathing,
- difficulty swallowing,
- changes in bowel or bladder habits,
- the appearance of blood in stool or urine, or
- persistent cough or voice changes.
- Blood and lymphatic cancers usually have symptoms of
- fever and
- unusual bruising.
Major Types of Cancers
Cancers are named and classified based on where they start in the body.
- A carcinoma is a cancer that creates solid tumors in epithelial tissue.
- A sarcoma is rare and is often related to bone cancers.
- A lymphoma applies to any cancer that begins in the lymphatic system.
- A leukemia refers to cancers of the blood-forming tissues, such as bone marrow.
Globally, cancer is the leading cause of death (World Health Organization [WHO], 2022). The most common types of cancer for males are prostate, lung, colorectal, and urinary bladder. For females, breast, lung, colorectal, and uterine cancers are the most commonly occurring. Cancer of the lung and bronchus results in the most deaths, followed by colorectal cancer (American Cancer Society [ACS], 2024a).
Brain Cancer
Brain tumors are dangerous whether they are benign or malignant due to the constricted amount of space in the skull. Benign tumors may grow and cause dysfunction and symptoms related to their position in the brain and tumor size. Symptoms are related to the space the tumor occupies and its effect on the brain. Common symptoms are headaches, nausea or vomiting, seizures, changes in vision, problems with speech or balance, and cognitive changes.
Types of brain tumors include gliomas, astrocytomas, oligodendrogliomas, meningiomas, and medulloblastomas. The names refer to the specific cell or neuron type in the brain from which they develop. Brain tumors can originate in the brain, although metastatic brain growths are also common. Treatment, especially surgery, depends on the location and type of brain tumor. Prognosis and outcomes also vary widely depending on the location and type of tumor.
Bone Cancer
Primary bone cancer originates in the bone. Types include osteosarcoma, chondrosarcoma, and Ewing sarcoma. Benign tumors result in the same symptoms as malignant tumors because bones are a finite space and cannot accommodate the additional space-occupying mass. Symptoms include localized bone pain, swelling, and possible fractures without traumatic injury. Radiation treatment for other cancers increases the risk of developing cancer of the bone.
Treatment of primary bone cancer varies according to the type and location of the tumor. Metastatic bone cancer occurs when other cancers, such as breast, lung, or prostate, spread to the bone. In the case of bone metastasis, the treatment is usually still determined by the primary tumor type, but this depends on a variety of factors. Bone metastasis is more common than primary bone cancer (ACS, 2024b).
Breast Cancer
Cancer of the breast tissue cells is the most common cancer in females across the world (WHO, 2024). Campaigns for screening and early diagnosis continue to improve survival rates (Todor et al., 2024). Risk of breast cancer occurrence can often be mitigated across lifestyle factors such as hormone use, diet, alcohol consumption, and physical activity.
Types of breast cancer are classified by their
- occurrence in the lining of the breast duct (ductal),
- presence in the milk glands (lobular), and
- relationship to hormone receptors or specific tumor markers (e.g., triple-negative breast cancer).
Symptoms vary by type of cancer but encompass changes in the appearance of breast tissue and breast function. Treatment options include solitary therapies and combinations of therapy types, such as surgery, radiation, chemotherapy medications, hormone therapy, or targeted therapy.
Colon and Rectal Cancer
Colon cancer and rectal cancer begin in the large intestine, often starting as a polyp in the inner lining, or epithelium. Colonoscopies are an effective screening tool, assisting in early detection. Nonhereditary occurrence of colon cancer, like breast cancer, can often be reduced by addressing lifestyle factors such as activity level, alcohol use, smoking, and intake of red meats and processed foods. Early symptoms are changes in bowel habits or stool appearance and microscopic blood loss. Later symptoms can include visible bleeding, fatigue, or weight loss.
Lung Cancer
Cancer of the lung is one of the leading cause of cancer deaths across the world. There are two main types: non-small cell and small-cell. There are many types of non-small cell lung cancer, each named for the types of cells and their appearance. One example is adenocarcinoma, which forms in the alveoli lining. Small-cell lung cancer is heavily linked to smoking and is very aggressive in how it grows and spreads, contributing to the lethality.
Symptoms of lung cancer include weight loss, a chronic cough, shortness of breath, hoarse voice, and recurrent respiratory infections. These symptoms are typically associated with smoking or chronic chemical exposure, which can result in delayed medical care that is ineffective for advanced cancer. Low-dose computed tomography (CT) scans should be used for regular screening.
Skin Cancer
Skin cancer is very common; one in five individuals in the United States will develop skin cancer (American Academy of Dermatology, 2024). The primary risk factor for its development is ultraviolet radiation exposure from the sun or from artificial sources such as tanning beds. Basal cell and squamous cell carcinomas are common and considered less lethal than melanoma, which metastasizes readily if not detected early (Figure 31.7). Melanoma can develop on the body in areas not typically exposed to the sun, such as between the toes as well as on genitals. Everyone, but particularly fair-skinned people, should pay close attention to changes in moles, lesions, and sores.
Link to Learning
The American Academy of Dermatology provides a body mole map to educate people on the ABCDEs of detecting melanoma, how to perform a self-examination, and sun safety.
Blood Cancer
Stem cells differentiate into mature cells (Figure 31.8) as follows:
- Red blood cells—erythrocytes—transport oxygen to tissues.
- Platelets—thrombocytes—assist with coagulation to stop bleeding.
- White blood cells—lymphocytes—provide an immune response to infection and disease.
Hematologic cancers affect the bone marrow and can cause changes to how blood cells are produced and their ability to perform their necessary functions in the body.
Initial symptoms of hematological cancers include fatigue and paleness due to reduced numbers of red blood cells (anemia), bruising or other abnormal bleeding due to low platelets (thrombocytopenia), and infections due to immature white blood cells (neutropenia). A reduced number of all blood cells (pancytopenia) is increasingly likely after treatment begins.
Blood cancers include leukemia, lymphoma, and myeloma. Leukemia is the profuse development of abnormal and immature white blood cells that are so numerous that they crowd out healthy cells. Lymphoma affects the lymphatic system, which changes how the lymph system functions as part of the immune system. Myeloma is a cancer that affects plasma cells, which are a type of white blood cell.
Therapies for hematological cancers include chemotherapy medications, targeted drug therapies, immunotherapy, radiation therapy to the bone marrow (often affecting the central nervous system), or a stem cell transplant to reestablish healthy bone marrow. Supportive therapies include transfusion of blood products and administration of colony-stimulating factors to induce the growth of white blood cells.
Leukemia
There are four main types of leukemia:
- acute lymphoblastic leukemia (ALL)
- acute myeloid leukemia (AML)
- chronic lymphocytic leukemia (CLL)
- chronic myeloid leukemia (CML)
Although leukemia is a disease of the white blood cells, pancytopenia is typical, sometimes at diagnosis and throughout treatment. Myeloblasts proliferate rapidly, crowding out the growth of healthy bone marrow components, affecting red blood cell count, platelet count, and the number of functioning white blood cells available.
Lymphoma
Lymphoma develops in the lymphatic system. Lymphomas are associated with certain infections, such as Epstein-Barr virus, HIV, certain strains of herpes virus, and hepatitis C seropositivity. There are two primary types of lymphoma: Hodgkin and non-Hodgkin. Both affect the lymphatic system and share similar risk factors, symptoms, diagnostics, and treatment options.
Reed-Sternberg cells are a defining feature of Hodgkin lymphoma (HL). HL tends to have a good prognosis. Non-Hodgkin lymphoma (NHL) is classified by subtypes of B-cell or T-cell, though there are more than forty major subtypes. It is the most common hematological malignancy worldwide, and is more common in males and those over the age of 65 years (Thandra et al., 2021).
In addition to typical hematologic cancer symptoms, patients may experience enlarged lymph nodes, night sweats, and fever. Treatment outcomes vary widely and depend on many factors, including how early treatment begins.
Myeloma
Multiple myeloma, also known simply as myeloma, is a type of blood cancer that affects plasma cells (Figure 31.9). A type of white blood cell, plasma cells produce antibodies; therefore, multiple myeloma—a condition in which abnormal plasma cells multiply uncontrollably within the bone marrow—leads to reduced immunity.
Bone pain and weight loss are common. Fatigue and increased infection risk also occur. Maintenance therapy and surveillance often continue for years after diagnosis with the goal of controlling the disease and relieving symptoms.