“Cancer” is a collective concept, the common name for a huge group of diseases that are united by one common property – the way out of the control of the processes of growth and reproduction (division) of cells. In the process of tumor development, one of the cells in the body changes and begins the endless process of reproducing its own kind. These cells subsequently spread throughout the body (see below in the section “What is metastasis”). The most common types of cancer are 10: eight affect organs, two affect the lymphatic and circulatory systems.
What types of cancer are there?
To date, more than 100 types of malignant tumors are known. As a rule, they are called according to the organ from which they originate, for example, the primary lung tumor will be called “lung cancer.” Sometimes additional refinements are applied, depending on the specific type of tissue from which the tumor originated. For example, “squamous cell lung cancer” is a subtype of lung cancer that has developed from a squamous epithelium lining the lumen of the bronchi. This is important when choosing a treatment method.
In addition, tumors can be divided into solid (“solid”), the cells of which form the tumor mass and tumors of the hematopoietic and lymphatic systems (hemoblastoses), which initially proceed as systemic diseases, i.e. involving more than one organ. For example, with leukemia, tumors originate from bone marrow cells, enter the bloodstream and circulate through the body with a blood stream.
Classically, the word “cancer” refers to tumors originating from the epithelium of the skin or mucous membranes. Tumors originating from other types of tissues, such as muscles, tendons, nerves, fat, bones, etc. called “sarcomas.”
Malignant tumors also include:
leukemia and multiple myeloma (primary bone marrow tumors);
lymphomas – tumors originating from the peripheral organs of the immune system, for example, lymph nodes;
melanoma – a tumor that develops from melanocytes, special cells that normally protect the body from the harmful effects of sunlight, they also form “moles”;
neuroendocrine and carcinoid tumors are tumors with hormonal activity.
What is the difference between malignant and benign tumors?
One should distinguish between benign and malignant tumors, their main differences are presented in Table 1. It should be noted that in some cases, benign tumors can reach significant sizes. Benign tumors, as a rule, do not pose a direct threat to the patient’s life, with the exception of tumors growing in the brain and spinal cord – these tumors can compress critical structures in these organs and lead to death or irreparable harm to the patient’s health.
How does cancer arise and how do tumor cells differ from normal ones?
Many normal cells have the ability to divide, but these processes occur in concert and stop or slow down when the need for the formation of new cells disappears. So, for example, wounding the skin stimulates the acceleration of cell division processes that form the skin. As soon as the wound is healed, the cell division rate again slows down to the level necessary only to update aging cells.
With the development of the tumor, everything changes. Its cells divide almost independently of external signals (autonomously), with the accumulation of mutations, they become less and less like normal ones, their previous functions are lost, but only one thing remains – reproduction. Tumor cells begin to actively absorb nutrients, grow and multiply. Over time, they begin to displace normal cells, acquire the ability to invasive growth (which means germination in other tissues and blood vessels) and metastasis (spread throughout the body with blood flow, lymph, along the vessels and nerves, and so on).
The reason for the appearance of tumor cells (oncogenesis) is the appearance of certain mutations in the DNA – violations in the genetic code of the cell that arise under the influence of external factors (for example, carcinogens, oncogenic viruses, etc. – see below) or in the process of natural cell division.