Cancers are among those most feared diseases in developed countries. Their incidence is gradually growing and they belong to the most common causes of death together with cardiovascular diseases. This article should give you simple and comprehensible information about cancers, their causes, manifestations and to a small extent their diagnosis, prevention and treatment.
This text is somewhat extensive and that is why I would like to divide it into more parts.
- Tumor types
- Causes of tumors
- Cancer formation
- Evaluation of cancers
- Symptoms of cancers
- Diagnosis of cancers
- Treatment of cancers
Tumors can be classified according to many aspects. I shall mention only few aspects that are, in my opinion, the most clinically significant.
Tumor types according to malignancy
a) Benign tumors
Benign tumors are unable to form local or distant metastases. Tumors of this type grow at different speeds and "only" compress the surrounding tissues. There are many of them, for example hemangiomas, lipomas or warts (tumors caused by a virus infection). These tumors are regarded as harmless, but this is not totally truth. The tumors can cause problems by the actual growth and damage of nearby anatomical structures. Very dangerous are benign brain tumors, because they can easily cause life-threatening intracranial hypertension. In addition, certain benign tumors may change into malignant, when left untreated for a longer time period.
b) Malignant tumors
These tumors are labeled as cancers. They grow aggressively and destroy adjacent anatomical structures. In addition, these tumors are capable of spreading by lymphatic fluid, or by blood, by forming secondary tumor lesions known as metastases. There are hundreds of such cancers, clinically most important are for example colon cancer, lung cancer, pancreatic cancer, esophageal cancer, prostate cancer, bladder cancer, cervical cancer, stomach cancer, kidney cancer, melanoma, penile cancer, tongue cancer, breast cancer, endometrial cancer, ovarian cancer, bone cancers, sarcomas, cancers based on blood cells (mainly leukemias and lymphomas), and many others. Malignant tumors can arise from any tissue in the body.
c) Semi-malignant tumors
These are specific tumors that do not form metastases, but they grow aggressively and actively destroy the neighboring. A classic example is basal cell carcinoma. This skin tumor is often found on the face and when left untreated, it may damage facial tissue including bones. Once it is surgically removed, the affected person is fully cured (assuming that the surgeon removed the whole tumor).
Primary and secondary tumors
a) Primary tumors
Primary tumor is the tumor mass in area, where the tumor originated from.
b) Secondary tumors
This is tumor tissue that is found in area different from the primary tumor site. The term "secondary tumor" is an equivalent of "metastasis". For, example, a patient may have stomach cancer (primary tumors) with liver metastases (secondary tumors).
There are many causes of cancer diseases. We can divide them into preventable and unpreventable. Naturally, we are interested in both groups. Knowledge of preventable causes may help us to use protective measures to decrease the tumor incidence. Knowledge of unpreventable causes may allow us to preventively screen those at high risk.
Age - Tumors can occur at any age, but their incidence typically increases with higher age. On the other hand there are special forms of tumors, which occur typically in children (Wilms' tumor).
Sex - Some tumors are highly- or totally dependant on the patient's sex. For example, breast cancer occurs mainly in women and endometrial or ovarian cancer occurs only in women, while prostate cancer affects only men.
Genetics - The origin and development of cancer genetics plays a role no doubt. Some cancers have a family history.
Contact with cancer-causing factors - These factors are chemical, physical and biological. Biological factors include mainly certain viruses that have been reported to influence formation of tumors. Great examples are HPV virus in cervical cancer and EBV virus in nasopharyngeal cancer in Africa and Chin. Physical factors are radiation and sunrays. Chronic excessive exposure to sunlight significantly increases risk of skin tumors, including the feared melanoma. Chemical factors are many substances that have reported carcinogenic effect - formaldehyde, heavy metals, many industrial organic compounds and particularly substances in cigarette smoke.
Lack of exercise, and unhealthy diet - Obesity, lack of physical exercise and unhealthy diet with high intake of proteins and fats accompanied by low intake of vitamins and dietary fiber increase risk of many tumors.
Weakened immunity - Immune system fights with cancers and destroys tumor cells. Therefore, it is logical that weakening immune system increase risk of malignant diseases. Classically, this is reported in advanced stages of HIV infection, so-called AIDS.
Oxidative stress - Processes known as the term "oxidative stress" are suspected from participating in aging and increased risk of cell mutations, which are very important for cancer patophysiology.
Cancer formation is a complex process. Our body is a multicellular organism, which is - unlike single-cellular organisms - composed of billions of cells. Individual cells have unique specializations and they organized into organs and tissues. Each of these organs and tissues do their predetermined function and they are dependent on each other - brain is the control center (it controls our body, but it needs delivery of oxygen and nutrients), kidneys eliminate waste products, lungs ensure oxygenation of tissues, liver serves as a chemical factory of the body, skeleton and muscles provide stability and motion, etc.
Reproduction is one of the essential characteristics of life and this is also true for single cells.
Take one single-cell bacterium and put it into an environment with plenty of nutrients. It will reproduce and multiply, until all nutrients have been consumed. However, in our multicellular, organism, the body can not let the cells to grow and reproduce as they please. There are many regulatory mechanisms that cautiously control cell's life and its reproduction. When a cell stops responding to these regulatory mechanisms and begins to proliferate uncontrollably, it may cause formation of a cancer. This situation is usually related to a mutation in the genetic information of particular cell. Development of a dangerous cancer, however, usually needs a whole sequence of mutations and it is typically a chronic process.
As the cell gets out of control, it can be targeted by our immune system as a potential threat. Tumor cells are destroyed by our immunity, but unfortunately, they may have many tricks to protect themselves. For example, they change their surface structures such that our immune system can not recognize them. Some types of cancer cells can even grow special ability to force any attacking immune cell to commit suicide.
Tumors and their attributes can be characterized according to so-called typing, staging and grading.
Typing specifies the exact type of tissue, from which the tumor develops. Typing is stated thanks to histological examination of a sample of the tumor mass. Sometimes, however, the result of biopsy may be uncertain and the typing is not possible.
Grading determines the maturity of the tumor. The higher is the grade, the less similar is the tumor tissue to the original tissue, from which it originates. Higher grade means also higher aggressiveness and dangerousness of the tumor. Grading is again determined by histological examination of a tumor sample.
Staging indicates the extension of tumor process in the body. We usually use the so-called TNM classification. TNM stage can be determined only after the patient is examined by imaging methods. The letter "T" stands for "tumor" and determines the extent of the primary tumor (size, growth into nearby anatomical structures, etc.). The greater is the local extent of the tumor, the greater is the "T" number.
The letter "N" means "Node" and it determines whether and how many local lymph nodes are affected by metastases. The higher is the number, the more massive is the affection. The value "N0" indicates that no local lymph node affection has been confirmed. The letter "M" determines whether there are any distant metastases, for example in the liver, lungs, brain, bones, etc. The value of M is either 0 (no confirmed metastases), or 1 (confirmed metastases).
For example, the TNM classification can be T2N0M1 in a certain tumor. That means the tumor has certain size (T2), that no local lymph nodes are affected by the tumor, but that we confirmed presence of distant metastasis (or metastases).
Cancers are very insidious and even-life threatening tumors may be asymptomatic for a long time. The symptoms may be divided into local and general.
Local manifestations can occur in all tumor types and they are caused by the tumor affection of local tissues, or organs. The problem is that majority of tumor symptoms may be also caused by other non-malignant diseases. For example, blood in stool may occur in colon cancer, but it is usually caused by hemorrhoids. The most local symptoms include:
Hoarseness lasting more than two weeks is suspicious and it accompanies tumors that affected vocal cords. Hoarseness also occurs in upper respiratory tract infections, but it usually disappears within o week or two.
It (either visible or occult) may be present in colon cancer, but it is also related to a large number of benign diseases.
Alternating diarrhea and constipation
Again, this symptom may be present in colorectal cancer.
This is a very unfortunate symptom. Sudden onset of painless jaundice may occur when the bile duct is compressed by a neighboring tumor (cancers of the gallbladder, biliary tract and pancreatic cancer).
Enlargement of lymph nodes may be caused either by tumors or by infections and other non-malignant diseases. We should be especially cautious when the enlargement is painless. General manifestations usually accompany advanced forms of cancers where there are present multiple distant metastases. The symptoms are result of defensive inflammatory response of the body to the tumor and of deficiency of nutrients and energy that are consumed by the tumor tissue. The general manifestations include:
If the body temperature is elevated above 37°C for a long time, it should be further examined. It may accompany chronic infections, autoimmune diseases and tumors.
If a person unintentionally loses around 10% of one's original weight within few months without a change in eating habits or without increase of physical activity, it should be regarded as serious sign. Weight loss in spread tumors is usually accompanied with significant reduction of muscle mass.
This symptom is frequent in cancer diseases and it is accompanied with elevated body temperature.
Sudden loss of appetite may also indicate presence of a tumor in the body. It is typically present in tumors of the digestive tract.
Diagnostic possibilities are very wide and slightly differ according to the particular type of tumor. Skin cancers can be seen by the naked eye, seen private eye, some tumors can be found by palpation (classically abdominal tumors) and tumors in the mouth and throat can be found by otolaryngological examination. Imaging methods are important in tumor diagnostics and in evaluation of the TNM classification (chest X-ray, ultrasound, computed tomography, scintigraphy, magnetic resonance imaging and others). Endoscopy is very important for diagnostics of cancers of hollow organs (esophageal, stomach and colorectal cancer, urinary bladder cancer, endometrial cancer, etc).
When possible, the diagnostic process of tumors should always include taking a sample of the tumor tissue for histological examination. Cytology is also possible, but it is less reliable and its negative result does not rule the malignancy.
Each patient receives individual treatment, which depends on the type of tumor, the extent of the malignant process and the patient's actual condition. The therapeutic methods can be combined to make the treatment more effective. More information can be found in article devoted to cancer therapy.
Surgical procedures involve removal the tumor mass. Surgery is commonly the only way to cure the cancers.
Chemotherapy uses toxic substances that damage both healthy cells of patient's body and tumor cells. However, tumor cells are generally more sensitive to chemotherapy. While the majority of normal cells have a potential to regenerate, the tumor cells die.
Radiotherapy is performed for a similar purpose as chemotherapy. Tumor cells are more sensitive to radiation exposure than normal cells.
This is a modern therapy used in some tumors. Biological treatment uses special substances that specifically damage the tumors. A classic example is compound bevacizumab, which blocks the tumor from producing its own blood vessels, and thus disrupts its nutrition.
Hormonal therapy can be used only in some tumors that are highly sensitive to hormone effects, for example prostate cancer and certain forms of breast cancer. Hormonal therapy aims to somehow dampen the hormone effect to decrease the tumor growth.
Palliative therapy includes all forms of treatment that does not cure the cancer, but that improve the quality of patient's life.