What is Cancer?

The human body is composed of trillions of cells. Each cell is regulated internally by genes and proteins and externally by various molecular signals. There are several types of unique cells that exist, each designed to function in a specific way. By consequence, cellular activity, life spans, and resilience to insults vary from one cell to the next. For example, superficial (epidermal) skin cells live an average of 28 days. This means that every month, our epidermis renews itself completely. This is a necessary function of the skin which enables itself to heal from trauma (i.e. lacerations, burns, etc) and to maintain a barrier against infection, amongst other things. In the absence of an active wound healing, skin renewal is not noticeable since every day an equal number of old skin cells are replaced by new ones through a process called cell division. Cell division is a process whereby a parent cell is cloned via genetic duplication resulting in the formation of two identical daughter cells. This process is critical to sustain life and normal functioning.

Many people are apprehensive about the topic of cancer. We often fear what we do not understand. I guess this is due to the fact that cancer is still not fully controlled despite all the advances in medicine. At one point or another in our lives, we may have witnessed family and friends succumb to this dreadful disease. The truth is some cancers are more aggressive than others, and as a result some cancers are more difficult to treat.

Cancer is a disease that results from altered cell function, more specifically genetic damage, in an actively dividing cell. Cells are exposed to various insults on a daily basis. Whether it be UV rays from the sun damaging skin cells, cigarette smoke damaging cells of the mouth, throat, and lungs, or carcinogens in food damaging gastrointestinal cells, our bodies need to overcome these insults in order to maintain normal functionality. The mechanisms by which cells respond to injury are either by self-repair or self-induced death. Cells are constantly undergoing genetic repair to reverse the ongoing damage caused by various agents. In the case that a cell cannot repair itself, it undergoes self-destruction. This is a critical feature to ensure the cell’s genetic material (i.e. DNA) remains unaltered. A genetic mutation is passed down to future cell generations when the error is not repaired prior to or during cell division. Therefore, the newly created cells contain the same error in its DNA as the parent cell. If these genetically altered cells continue to divide, they will pass on this mutation to all of their descendants.

Our bodies are continuously exposed to harmful agents that are potentially damaging to DNA causing genetic mutations. Regardless, not all genetic mutations result in cancer. There are multiple safeguards exist to prevent DNA mutations. Due to the protective nature of DNA, many genetic mutations will have absolutely no effect on cell function or division and thus are silent mutations. Some mutations result in poorly functioning cells that are not viable and thus will die off before passing down the mutation. However, in certain situations, the mutation alters cell function in such a way that the cell remains viable and it is passed down to subsequent generations. Despite these conditions, not all mutations that are passed down result in cancer. Actually, only a small proportion will result in cancer otherwise it would be very prevalent even at a young age.

A neoplasm is defined as "a new growth." Cancer is a malignant neoplasm that is characterized by uncontrolled cellular growth, invasion into adjacent tissues, and possibly metastasis (distant spread via blood or lymph). On the other hand, not all neoplasms are cancerous. Benign masses or tumours do not invade into adjacent tissue. The significance of this is that once a benign mass is entirely removed, there is no recurrence and no need for any chemotherapy or radiotherapy. That is to say, similar to cancers, benign tumours arise from genetic mutations but are locally contained and do not spread distantly.

Cancers occur when the DNA mutation affects the genes responsible for regulating cell division. The major classes of genes that influence cell division in cancer are oncogenes and tumour suppressor genes. Oncogenes are genes that, when activated, induce the formation of development of cancer. In a normally functioning cell, regulatory genes, named proto-oncogenes, are necessary to ensure proper cell proliferation (i.e. division) and differentiation (i.e. maturation). In the case that a proto-oncogene is subject to a mutation that augments its expression, it becomes known as an oncogene and promotes tumour formation. On the other hand, a tumour suppressor gene functions as an anti-oncogene by suppressing uncontrolled cell proliferation. Since there are two copies of every gene in the human body, both tumour suppressor genes would have to be separately inactivated in order for unregulated cell division to occur.

There are several risk factors that increase the chance of developing cancer. These include lifestyle, genetics, environmental exposure, and occupational exposure. Lifestyle choices such as diet, habits (smoking, alcohol, recreational drugs), and level of activity (physical, sexual) may all have contributory influences. In terms of genetics, important risk factors include personal medical history, congenital anomalies, inherited anomalies, family history. Lastly, environmental and occupational exposure to various chemicals, radiation, and gases may be detrimental to our health.

Types of cancer

The colloquial meaning of the term "cancer" does not hold much informative value in the medical vocabulary. As mentioned previously, different types of cancers carry different prognoses. One of the reasons for this is due to the primary site from which the cancer originated. In fact, cancer is ultimately classified by the cell type from which it arises.

The classifications of cancer include: carcinoma, sarcoma, leukemia/lymphoma, blastoma, and germ cell. The most common cancer type is carcinoma. By definition, a carcinoma is a cancerous transformation of one of the cells that make up the epithelium. The epithelium is the superficial layer of cells that normally protects the body from, and interacts with, the environment. Our skin, the lining of our digestive system or respiratory tract are all examples of epithelia. Each have distinct functions, but share the same embryonic origin. Sarcomas arise from what is called the connective tissue. The connective tissue is there to 'connect' underlying structures and together. Leukemias/Lymphomas are cancers originating from leukocytes (white cells) and lymphocytes, respectively. Certain leukemias are more common in young people, including children. For example, acute lymphoblastic leukemia is the most common cancer in children. Germ cell cancers arise from totipotent cells that are normally found in the ovaries or testes, but may present with cancer anywhere in the body. Blastomas are cancers that form from stem cells. Stem cells are progenitor cells, in other words immature cells that have the potential to develop into various specialized cells. Blastomas can develop from a variety of tissues.

Signs and symptoms

Common signs and symptoms of cancer include weight loss, reduced appetite, fatigue, bleeding and/or pain. Certain cancers have classic symptomatology. For example, lymphoma is commonly characterized by ''B symptoms:" fever, chills, night sweats. Not uncommonly cancer is asymptomatic, especially lung and ovary. More specific symptoms vary among cancers.

Prevention and Screening

The best treatment in any scenario is prevention. If you smoke, then quit. If you drink more than two servings of alcohol per day, then you should cut down. If you eat lots of fatty foods, including red meat, anything that is fried, or processed foods containing large amounts of saturated fats, then you should modify your diet. Prevention is also a key factor in the workplace, especially for those exposed to potentially harmful chemicals or vapours, radiation, or other toxic substances.

The next best approach to fighting cancer is to screen for it. Screening tests are designed to detect cancers at a very early stage thereby increasing the chance of cure. Examples of screening tests are pap smears for cervical cancer, colonoscopy for colon cancer, mammogram for breast cancer, or digital rectal exam for prostate cancer. Unfortunately, not every cancer can be screened for. Lung, pancreas, and ovarian cancers are all examples of cancers that present at a late stage because they are relatively asymptomatic and difficult to screen. The ultimate purpose of screening tests is to save lives and avoid unnecessary suffering.