8.1 Introduction to Cancer and Phases of Cancer Therapy

Introduction to Cancer

Cancer is a disease of uncontrolled cell growth driven by genetic mutations. These mutations accumulate over time, transforming normal cells into cells that divide without the usual checks and balances. Understanding how cancer develops, what types exist, and how they're classified gives you the foundation you need before diving into the pharmacology of cancer treatment.

Process of Cancer Development

Cancer begins when normal cells acquire genetic mutations that disrupt the controls on growth and division. These mutations can be inherited (passed from parents) or acquired through exposure to environmental carcinogens like tobacco smoke or UV radiation. A single mutation usually isn't enough. It's the accumulation of multiple mutations over time that transforms a normal cell into a cancerous one.

Once a cell becomes cancerous, it gains several key characteristics (sometimes called the "hallmarks of cancer"):

• Sustained proliferative signaling: Cancer cells generate their own growth signals, so they continuously divide without needing external prompts.
• Evasion of growth suppressors: Normal cells have built-in brakes (tumor suppressor genes) that limit division. Cancer cells bypass these controls.
• Resistance to apoptosis: Apoptosis is programmed cell death, the body's way of eliminating damaged cells. Cancer cells resist this process and survive despite damage.
• Angiogenesis: Tumors stimulate the formation of new blood vessels to supply themselves with oxygen and nutrients.
• Invasion and metastasis: Cancer cells can break away from the primary tumor and spread to distant sites through blood or lymph.
• Replicative immortality: Normal cells can only divide a limited number of times. Cancer cells bypass this limit and divide indefinitely.

Genetic vs. Environmental Cancer Factors

Genetic factors involve inherited mutations that increase cancer risk:

• Mutations in tumor suppressor genes like BRCA1 and BRCA2 significantly raise the risk of breast and ovarian cancers. These genes normally help repair DNA or trigger apoptosis, so when they're defective, damaged cells are more likely to survive and become cancerous.
• Mutations in proto-oncogenes (such as RET or PTEN) can convert them into active oncogenes that promote uncontrolled growth.
• A strong family history of specific cancers often signals inherited genetic mutations worth screening for.

Environmental factors are responsible for a large proportion of cancers:

• Carcinogen exposure: Tobacco smoke, UV radiation, and asbestos directly damage DNA and cause mutations.
• Chronic inflammation: Infections like hepatitis B/C and H. pylori create a prolonged inflammatory environment that promotes tumor development.
• Dietary factors: High-fat, low-fiber diets are associated with increased risk of colon and breast cancers.
• Lifestyle factors: Physical inactivity and obesity contribute to the development of multiple cancer types by altering hormone levels, promoting inflammation, and affecting immune function.

Types of Cancer and Features

Cancers are classified by the tissue they originate from. This matters for treatment because different tissue types respond to different therapies.

• Carcinomas arise from epithelial cells and are the most common cancer type. Examples include lung, breast, colon, prostate, and skin cancers. They're further subclassified by cell type, such as squamous cell carcinoma (from flat surface cells) or adenocarcinoma (from glandular cells).
• Sarcomas develop from connective tissues like bone, cartilage, muscle, and fat. Examples include osteosarcoma (bone) and liposarcoma (fat). Sarcomas are relatively rare.
• Leukemias originate in blood-forming tissue (bone marrow) and involve abnormal production of white blood cells. They're classified by the cell line affected (myeloid or lymphoid) and the speed of progression (acute or chronic). Examples: acute myeloid leukemia (AML), chronic lymphocytic leukemia (CLL).
• Lymphomas develop from cells of the lymphatic system, including lymph nodes and the spleen. The two main categories are Hodgkin's lymphoma and non-Hodgkin's lymphoma, both characterized by abnormal lymphocyte accumulation.
• CNS tumors arise from brain and spinal cord tissues. Examples include gliomas (from glial cells), meningiomas (from the meninges), and medulloblastomas (from the cerebellum). CNS tumors can be benign or malignant and are classified by cell type and location.

Tumor Classification and the Cell Cycle

Tumors are classified as either benign or malignant, and the distinction is clinically significant:

• Benign tumors grow slowly, are well-differentiated (they still resemble normal tissue), and stay localized. They don't invade surrounding tissue or metastasize.
• Malignant tumors grow rapidly, are often poorly differentiated, and can invade nearby tissues and spread to distant sites.

The cell cycle is central to understanding cancer. Normal cells move through tightly regulated phases of growth and division (G1, S, G2, M). Cancer develops when this regulation breaks down, allowing cells to divide without proper checkpoints.

DNA repair mechanisms normally catch and fix mutations before they're passed to daughter cells. When these repair pathways are defective (as in BRCA mutations), genetic errors accumulate faster, accelerating the path toward cancer. This is also why many chemotherapy drugs target specific phases of the cell cycle, a concept you'll revisit throughout this unit.

Phases of Cancer Therapy

Cancer treatment isn't a single event. It unfolds across multiple phases, and the approach depends on the cancer type, stage, and patient factors. Here's how the phases typically progress:

1. Diagnosis and staging identify the cancer type and how far it has spread, which determines the treatment plan.

   • Diagnostic tools include imaging (CT, MRI, PET scans), biopsy (tissue sampling), and blood tests (including tumor markers).
   • Staging uses the TNM system: T = tumor size, N = lymph node involvement, M = presence of distant metastasis. Higher numbers in each category indicate more advanced disease.

2. Surgery aims to physically remove the tumor and/or affected lymph nodes.

   • Surgery serves multiple purposes: diagnosis (biopsy), staging (assessing spread), and treatment (tumor removal).
   • Examples: lumpectomy (breast cancer), prostatectomy (prostate cancer), colectomy (colon cancer).

3. Radiation therapy uses high-energy radiation to damage the DNA of cancer cells, killing them or stopping their division.

   • It can be delivered externally (external beam radiation) or internally (brachytherapy, where a radioactive source is placed near or inside the tumor).
   • Radiation is often used before surgery (to shrink tumors), after surgery (to destroy remaining cells), or alongside other treatments.

4. Chemotherapy is a systemic treatment, meaning drugs circulate throughout the body to kill rapidly dividing cells wherever they are.

   • Routes of administration include oral, intravenous, intrathecal (into spinal fluid), and intraperitoneal (into the abdominal cavity).
   • Chemotherapy can serve as the primary treatment or be combined with surgery and radiation.

5. Targeted therapy uses drugs designed to attack specific molecular targets involved in cancer growth.

   • Examples: tyrosine kinase inhibitors (small molecules that block growth-signaling enzymes) and monoclonal antibodies like trastuzumab, which targets HER2-positive breast cancer cells.
   • Because these drugs are more selective than traditional chemotherapy, they tend to cause fewer side effects on normal cells.

6. Immunotherapy harnesses the patient's own immune system to recognize and destroy cancer cells.

   • Examples: immune checkpoint inhibitors (pembrolizumab, nivolumab) that "release the brakes" on immune cells, and CAR T-cell therapy, where a patient's T-cells are engineered to target cancer.
   • Can be used alone or combined with other modalities.

7. Hormone therapy targets cancers that depend on hormones for growth, primarily breast and prostate cancers.

   • It works by blocking hormone production or blocking hormone receptors on cancer cells.
   • Examples: tamoxifen (blocks estrogen receptors in breast cancer) and leuprolide (suppresses testosterone in prostate cancer).

8. Palliative care focuses on symptom relief and quality of life rather than curing the disease.

   • It can be provided at any stage of treatment, not just at end of life. This includes pain management, nutritional support, and emotional support.
   • Hospice care is a specific form of palliative care for patients with a life expectancy of roughly 6 months or less.

Additional Treatment Approaches

Two terms you'll see frequently in oncology nursing:

• Adjuvant therapy is given after the primary treatment (usually surgery) to reduce the risk of recurrence. For example, chemotherapy after a lumpectomy targets any microscopic cancer cells that may remain.
• Neoadjuvant therapy is given before the primary treatment to shrink tumors and improve surgical outcomes. For example, chemotherapy before surgery can reduce tumor size enough to allow a less invasive procedure.

The ultimate goal of cancer treatment is remission, where no detectable signs of cancer remain and symptoms are reduced or eliminated. Remission can be partial (tumor shrinks significantly) or complete (no detectable disease), though complete remission does not always mean the cancer is permanently cured.