The term “cancer” does not refer to a single disease, but encompasses a group of distinct conditions that can affect almost all the cells of our body.
We have talked about it with Dr. Luca Toschi, an Humanitas oncologist.
Normally, the cells in our body grow and divide into new cells; as they age or become damaged, they die and are replaced by new cells. In cancer, this process is abnormal: damaged cells survive, eventually dividing to the point of creating an accumulation of cells, which we call a tumor.
Tumors can be solid, when they are masses of tissue, but also liquid, as in the case of blood cancers.
Benign and malignant tumors
When we talk about tumors, we usually refer to malignant tumors (or cancer), however we often hear about “benign” tumors as well.
Benign tumors are characterized by some cells growing more than they should, creating masses that can reach considerable sizes – yet remaining delimited and not invading surrounding organs – retaining the characteristics of the original tissue. Benign tumors also do not produce metastases, not spreading to other parts of the body through the blood or lymphatic vessels, colonizing other organs or tissues, as do malignant tumors. Generally, once removed, benign tumors do not tend to recur as malignant tumors often do.
Malignant tumors (or cancer) can invade nearby tissues or spread to other organs. In fact, when they grow, some cancer cells can detach from the site of origin, travel through the blood or lymphatic system to distant places in the body, and produce metastases.
The characteristics of cancer cells
Cancer cells have characteristics that differentiate them from normal cells and allow them to grow uncontrollably. Furthermore, cancer cells are less specialized than normal cells: that is, while normal cells are transformed into types of cells with specific functions, cancer cells do not mature into their particular specialization, partially due to their peculiarity of ignoring the signals that would induce them to do so. What is more, cancer cells have abnormalities in the functioning of apoptosis, which is the natural process of genetically controlled programmed cell death, in which cells are eliminated from the body to maintain tissue health. Without apoptosis, the body cannot eliminate unnecessary cells, which thus form a mass.
Cancer cells are also able to influence their microenvironment, i.e. the cellular and extracellular environment around the tumor, which includes the surrounding blood vessels, immune cells, connective cells, and more.
Cancer cells can also evade the immune system, which protects the body from infections and other conditions through a collection of specialized organs, tissues and cells. Indeed, although the immune system normally eliminates damaged or abnormal cells in our body, some cancer cells are able to hide from it.
How cancer forms
Cancer is a genetic disease caused by changes in the genes that control how cells work and reproduce. Genetic changes that cause cancer are only rarely passed on from parents to children, so cancer is generally not an inherited disease. In fact, in the vast majority of cases these genetic changes appear during the life of an individual due to errors during cell division or due to damage to the DNA caused by such risk factors as chemicals found in tobacco or UV radiation.
How cancer spreads
The process by which cancer cells spread to other parts of the body is called metastasizing. A tumor that has developed somewhere other than where it originated is considered metastatic cancer. Metastatic cancer conserves the name of the original site and is made up of the same type of cancer cells as the primary cancer; for example, breast cancer that spreads and forms metastatic cancer in the lungs is metastatic breast cancer, not lung cancer.
Metastatic tumors can cause serious damage to the functioning of the body; most people who pass away from cancer die due to metastases.
Not all tissue changes are cancer
Not all tissue changes are cancerous; however, some changes can turn into cancer if left untreated, and it is good to keep them monitored. Here are a few examples:
- Hyperplasia occurs when the cells of a tissue divide faster than normal, causing an accumulation of cells that in turn leads to an increase in the size of a particular organ or tissue. It can be caused by various factors and conditions, including chronic irritation.
- Dysplasia is a more serious condition than hyperplasia and refers to a morphological, quantitative and qualitative variation of a cellular structure of a certain tissue, often epithelial. In the case of dysplasia, the cells appear “abnormal” in shape, color or structure, as their characteristics differ from those of healthy cells.
- Carcinoma in situ is a proliferation of abnormal epithelial cells, which have morphological and biological characteristics of malignancy, but which do not possess the ability to invade the tissues beyond the basement membrane: this means that it cannot reach blood vessels, lymphatic vessels and, therefore, cannot metastasize.