Cancer

Introduction

Cells in your body are constantly growing and dividing. Sometimes, cells begin to multiply in an uncontrolled fashion and develop an abnormal tissue or growth. The abnormal cells or growth have no useful physiological purpose in the body and can cause irreparable damage. These abnormal growths are called neoplasms. The study of neoplasms is called oncology. A neoplasm can be benign or malignant. Both types of neoplasm can cause a lump to form in the tissue, called a tumor. Tumor is a word that's used synonymously with neoplasm. A benign neoplasm is sometimes referred to as a benign tumor. A malignant neoplasm is called cancer. Cancer isn't always a solid tumor. Cancer can originate in body cells that are floating around, such as blood cells and lymph cells. These cells aren't fixed to a particular organ or body structure. Abnormalities in these floating cells are even more dangerous because cancer can spread to various body parts much quicker. 

 

Causes of Cancer

The following characteristics differentiate benign tumors from cancerous tumors:

• Benign tumors grow slowly; cancer grows rapidly.
• Benign tumors are often enclosed by a well-defined membrane border; cancerous tumors are non-encapsulated, with an ill-defined membrane border, and project into surrounding tissues.
• Benign tumors don't usually cause harm to the body unless they're large and interfere with the proper functioning of surrounding tissue. For example, due to the limited space in the cranium, benign brain tumors may be harmful to the surrounding brain tissue. Malignant neoplasms or cancer cells are always dangerous, no matter where they are, since the cells will travel through blood and lymph to invade tissues near and far.
• Benign neoplasms don't usually grow back after surgical removal; cancer cells frequently regenerate after surgical removal.

 

Normal cells can transform into cancerous cells through a process called carcinogenesis. Researchers believe this process occurs in the genetic code of the cells, the deoxyribonucleic acid (DNA) of chromosomes. In normal cell division, a group of genes called proto-oncogenes handle the proteins necessary for that division. In normal DNA, DNA repair genes and tumor suppressor genes can reverse damage in the cells.

The DNA repair genes correct any abnormalities in cells before they divide. The tumor suppressor genes control the growth rate of cells, instructing them to kill themselves (apoptosis) if they start multiplying too rapidly or if the DNA repair genes can't fix the defect. If these protooncogenes mutate, they become known as oncogenes.

Oncogenes instruct cells to make proteins that result in excessive cell growth and abnormal division. These oncogenes can convert normal cells to cancer cells. If the oncogene has affected the DNA repair genes and the tumor suppressor genes, the cells have no instructions to slow down. Thus, they continue to produce abnormalities in daughter cells faster and faster.

Once the genetic material of a cell has transformed, or mutated, the correct genetic code is lost. During mitosis, or cell division, the oncogene parent cell will produce two new abnormal cells instead of healthy cells. The mutated cells grow quickly in number and form a tumor. A change in DNA structure can be passed down to subsequent generations through the transfer of DNA from parents to a fetus.

 

Some cancers result from a defect in the arrangement of DNA chromosomes in the original egg and sperm that created the individual. A child can be born with a defect in the chromosomes that will cause mutation if activated. The factors that activate a gene are unclear. Some cancers have biological causes, relating to factors such as aging and reproductive history. These changes happen during a person's lifetime. They're called acquired, or somatic, mutations.

For instance, the risk of prostate cancer increases substantially in men over age 65. And women who never had children, or had their first child after age 30, are at higher risk of developing breast cancer. At least half of all cancers are believed to have direct environmental causes. Chemicals, drugs, viruses. and other agents called carcinogens can lead to changes in DNA, and thus to cancer. A major carcinogen is tobacco smoke, which accounts for 90 percent of all lung cancers.

 

The following carcinogens are commonly found in our working and living environments:

• Household chemicals: Benzene in glues, insecticides, tobacco smoke, and additives in processed foods
• Industrial pollutants: Arsenic from mining and smelting, asbestos from construction, benzene from oil refineries 
• Radiation: Ultraviolet rays from the sun, X-rays and radioactive substances from diagnostic and therapeutic procedures
• Hormones: Primarily the synthetic estrogen diethylstilbestrol (DES)
• Viruses: Hepatitis B virus can lead to liver cancer and human papillomavirus is known to cause cervical cancer.

 

Early Signs of Cancer

Usually, the growth of malignant cells doesn't cause noticeable symptoms right away, but physicians who know what to look for can detect early signs of cancers. The American Cancer Society recommends regular physical exams and has publicized the acronym CAUTION, which states the following seven early danger signs of cancer:

C Change in bowel habit 

A A sore that doesn't heal

U Unusual bleeding or discharge

T Thickening of tissue or a lump

I Indigestion or trouble swallowing

O Obvious changes to moles or warts

N Nagging cough or persistent hoarseness 

 

Types of Cancer

There are many known types of cancer. They're classified according to the type of tissue cells they grow. Classifications containing the suffix -oma, which means "tumor", connected to a body part word, are almost always benign. Examples include papilloma (an epithelial tumor), adenoma (a tumor originating in a gland), or osteoma (a bony tumor usually found on the skull). But the combining forms carcin(o) and sarc(o) turn the suffix -oma into a serious illness. Blood and lymph cancers typically originate in the bone marrow. 

Carcinomas are cancers that originate in the epithelial tissues and include most breast, stomach, uterine, skin, tongue, and glandular cancers. Some examples are esophageal carcinoma, carcinoma of the breast, and squamous cell carcinoma of the skin. The great majority (about 90 percent) of cancers are carcinomas. 

Sarcomas are cancers that originate in connective tissues such as bones, muscles, and lymph. They're often named by adding the suffix -sarcoma to the combining form for that tissue. Examples include osteosarcoma, cancer originating in bone tissue; chondrosarcoma, cancer originating in cartilage; and liposarcoma, cancer originating in fat tissue. Sarcomas are the minority form of cancer, but they're generally more fast-growing and deadly than carcinomas.

Blood and lymph cancers usually originate in the bone marrow where blood and lymph cells are produced. Examples of these cancers include leukemia, non-Hodgkin's lymphoma, and multiple myeloma. 

 

Grading and Staging

When physicians classify malignant tumors, they may use a number of techniques. Two systems, grading and staging, are in widespread use to help physicians study cancer and establish consistent diagnosis and treatment procedures. Several grading and staging systems are available for specific types of neoplasms. There's also a general grading and staging system that may be used alone or in combination with a tumor-specific system to give healthcare providers the most detailed picture possible of the disease in question.

Grading is the microscopic study of a tumor specimen to determine the degree of cell differentiation. The most common grading scale is the Broders's index, which has the following four classifications:

Grade 1 means the tumor is highly differentiated, or close to normal parent tissue, but some abnormality is present.

Grade 2 means the tumor is moderately differentiated, or not as close to normal parent tissue and the cells are fairly irregular.

Grade 3 means the tumor is poorly differentiated, or quite far from normal parent tissue, and the tissue of origin may even be difficult to identify.

Grade 4 means the tumor is dedifferentiated, or anaplastic, and so immature and primitive that it's virtually impossible to tell what is the parent tissue.

Grade 1 indicates an early stage of abnormality, and Grade 4 indicates a full-blown malignancy. The prognosis is good for patients with Grade 1 tumors and worsens as the grades go up.

*Cancer is sometimes classified as stage I through stage IV depending on how far the tumor cells have spread from the original site. Stage I is assigned when the tumor cells are localized at the original site only. As the tumor spreads further from the original site, the stage level increases to stage II and stage III. Stage IV is assigned when cancer is spread to many organs throughout the body. Stage 1 has the best chance of successful treatment, and treatment success declines as the stage number increases.

 

Cancer Treatment

Cancer treatment depends on various factors, such as the type, the location, and the grading and staging of cancer. If cancer is in the form of a solid tumor and in its initial stage, it's likely that surgical removal followed by radiation treatment is sufficient to fully treat the patient. Radiation therapy is used post-surgery to target any remaining cancer cell fragments by exposing the cancer site to direct radiation treatments. Treating cancer with medication is known as chemotherapy. Chemotherapy is often combined with surgery and radiation to treat advanced stages of cancer. The goal of cancer chemotherapy is to introduce agents that will kill malignant tissue while leaving all the healthy tissue intact. The term chemotherapy regimen means there are two or more antitumor drugs being used to destroy the malignancy. If everything goes well, the patient will go into remission, meaning all signs of the disease will disappear. Antitumor drugs are referred to as antineoplastic agents, meaning they inhibit the maturation and reproduction of malignant cells. Different drugs are used, and in different combinations, depending on the type, stage, grade, and location of cancer as well as the patient's condition.

 

Alkylating agents kill rapidly proliferating malignant cells by preventing DNA replication. These medications work by attaching an "alkyl" group to the DNA or otherwise damaging the DNA. While fast dividing cancer cells are unable to detect this error, resulting in DNA damage and cancer cell death, healthy cells generally can correct this error. Nitrogen Mustard was one of the first alkylating agents used to treat cancer and was also one of the modern drugs to effectively treat cancer. One of the disadvantages of these drugs is their non-specificity to the cancer cells. Commonly used alkylating and alkylating-like agents are:

• Carboplatin (Paraplatin)
• Carmustine (BiCNU)
• Chlorambucil (Leukeran)
• Cisplatin (Platinol)
• Cyclophosphamide (Cytoxan)
• Mechlorethamine hydrochloride (Mustargen)
• Oxaliplatin (Eloxatin)
• Temozolomide (Temodar)

Antimetabolites are a class of medications commonly used to treat various cancers. These medications inhibit certain metabolites that are essential to carry out cell metabolism, causing defects in cell growth and multiplication. Since cancer cells divide and grow exponentially, these medications act more quickly on growing cancer cells than on normal, healthy cells. Just like any other chemotherapy medication, there's some damage to healthy cells along with cancer cells. To avoid damage to healthy cells, chemotherapy regimens are often given in cycles of every three to six weeks. The time between the chemotherapy regimens allow the body to recover from the side effects. Commonly used antimetabolites are:

• Azathioprine (Imuran)
• Cytarabine (Cytosar-U)
• Fludarabine (Fludara)
• Fluorouracil (5-FU)
• Mercaptopurine (Purinethol)
• Methotrexate (Trexall)

Antitumor antibiotics aren't the same as antibiotics. These agents prevent the normal replication of nucleic acids (DNA and RNA). These medications work by binding to the DNA to halt the RNA synthesis, in turn causing cancer cell death. The antitumor antibiotics commonly used are:

• Bleomycin (Blenoxane)
• Dactinomycin (Cosmegen)
• Daunorubicin (Cerubidine)
• Doxorubicin (Adriamycin)
• Epirubicin (Ellence)
• Idarubicin (Idamycin)
• Mitomycin (Mutamycin)
• Mitoxantrone (Novantrone)

Vinca alkaloids, also called plant alkaloids, are drugs derived from plants. They inhibit cell division at a specific step during the cell cycle. The vinca alkaloids commonly used are:

• Vinblastine (Velban)
• Vincristine (Vincasar)
• Vinorelbine (Navelbine)

Hormones are essential for conducting many key processes and reactions in your body. Unfortunately, hormones may at times trigger or aid in the development of certain cancers such as breast cancer, prostate cancer, and other cancers of the reproductive organs. Antihormones (agents that counteract hormones) and certain steroid analogs of hormones are commonly used to treat these types of cancers. Hormone analogs compete to bind to the hormone receptor sites to stop or reduce cancer cell growth. These agents are successfully used to treat various hormone-dependent cancers, such as estrogen-dependent breast cancer. The hormone-like agents commonly used are:

• Anastrozole (Arimidex)
• Bicalutamide (Casodex)
• Exemestane (Aromasin)
• Letrozole (Femara)
• Tamoxifen (Soltamox)
• Toremifene (Fareston)

Immunomodulating drugs work by activating the immune system or modifying a biological response to an unwanted stimulus such as a tumor. These drugs either boost your body's immune system so that it's more active in destroying cancer cells, or they make the cancer cells more evident to the immune system. They may also enhance your body's ability to recover from other therapies, such as radiation and chemotherapy.

Monoclonal antibodies are used successfully as immune system modulators to treat many types of cancers. These antibodies are produced in the laboratory. Scientists use the tumor material itself to determine which antigens are present on the neoplasm, identify which antibodies work against that particular antigen, and then replicate these antibodies. They can then inject the antibodies directly toward the tumor. They can even attach radiological or chemotherapeutic materials to the antibodies that will enhance the disease-fighting ability of the antibodies themselves. This therapy has been successful in treating leukemia and lymphoma. The monoclonal antibodies commonly used are:

• Bevacizumab (Avastin)
• Cetuximab (Erbitux)
• Rituximab (Rituxan)
• Trastuzumab (Herceptin)
• Siltuximab (Sylvant)

Interferons are natural proteins produced by cells in reaction to viruses or bacteria. Interferons inhibit viral strains from reproducing, trigger microphages to engulf or eat cancer cells, and increase antigens so lymphocytes can produce antibodies against them. Interferons are used in the treatment of malignant melanoma (a type of skin cancer), some types of leukemia, non-Hodgkin's lymphoma, and AIDS-related Kaposi's sarcoma. The interferon drugs commonly used are:

• Interferon Alfa-2b (Intron A)
• Peginterferon Beta-1a (Plegridy)

 

Side Effects of Chemotherapy

Antineoplastic therapy is a dangerous undertaking. The drugs are strong enough to kill cancer cells, and also likely to kill rapidly proliferating healthy tissue, especially in the GI tract, the scalp, and the bone marrow. Common side effects of chemotherapy medications include hair loss, pain, fatigue, nausea, vomiting, diarrhea, stomatitis, and reduced blood cell production. 

Patients are susceptible to infection because of a weakened immune system. Patients undergoing chemotherapy are often weak and require many medications pre- and post-chemotherapy to manage the serious side effects of chemotherapy.

Nausea and vomiting induced by chemotherapy medications are notorious. The best management for nausea and vomiting is to give the appropriate medications prior to the initiation of chemotherapy and continue for three to five days after completion of the chemotherapy regimen. Once patients start feeling the symptoms of nausea, it's very difficult to treat with even the strongest anti-nausea medications. It's very important to instruct patients to continue taking prescribed nausea medications for prevention.

Chemotherapy-Induced Nausea and Vomiting Medications

The following medications are commonly used to treat chemotherapy-induced nausea and vomiting:

• Dexamethasone (Decadron)
• Granisetron (Kytril)
• Lorazepam (Ativan)
• Ondansetron (Zofran)
• Prochlorperazine (Compazine)

Stomatitis is an inflamed and sore mouth. There are different types of stomatitis. It's caused by irritated mucous membranes in the mouth. Chemotherapy medications often kill rapidly dividing cells of the mucous membrane in your mouth, leading to irritation and swelling. Patients are often prescribed topical anesthetics such as Lidocaine (Xylocaine) to apply locally for the numbness effect. 

Leukopenia is defined as a reduction in the number of leukocytes in the blood. Patients with a decreased level of leukocytes or WBCs are at a higher risk to catch infections because WBCs are the primary cells that protect the body against infections. Medications on the market called granulocyte-stimulating factors help increase the production and maturation of leukocytes. The following two medications are commonly used to boost the levels of WBCs after chemotherapy:

1. Filgrastim (Neupogen)

2. Pegfilgrastim (Neulasta)

Pain. Patients often need pain medications to control aches and pains due to chemotherapy. The following pain medications are commonly used:

• Acetaminophen (Tylenol)
• Ibuprofen (Motrin)
• Hydrocodone/acetaminophen (Vicodin)
• Acetaminophen/codeine (Tylenol #3)
• Oxycodone (OxyContin)
• Morphine Sulfate (MS Contin)

Fatigue. Since chemotherapy medications also effect normal cells in the body, it's common for patients to feel very tired while on chemotherapy medications. A well-balanced diet and rest are important to keep the body energized to cope with the disease.

Alopecia is defined as hair loss. Patients often have to wear wigs or scarves to cover their scalp. Hair grows back once chemotherapy treatment is completed. 

 

Key Points

• Cells have highly regulated and highly controlled ways of directing and maintaining body processes, so when anything goes wrong in these highly controlled processes, cells start to divide, grow, and multiply erratically. This uncontrolled growth leads to the formation of tumors.
• When tumors are normal healthy cells in abundance, this is called a benign tumor.
• Benign tumors are much less dangerous than cancerous tumors because these tumors remain localized.
• When a tumor is made up of deformed cells, it's called a malignant or cancerous tumor.
• Cancer is highly treatable during initial stages with the use of chemotherapy, surgery, and radiation, but once a cancer has metastasized from its original site to the other parts of the body, it becomes difficult to treat and patients have a poor prognosis. 
• Cancers can be solid tumors but could also be in the cells and fluids that circulate throughout your body. Examples of this are blood cancer and lymphoma (cancer of the lymph cells).