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Cancer, called disease of the century, is one of the leading causes of human death in Western countries. In 2018, 18.1 million cases were diagnosed worldwide with 9.6 million associated deaths. However, many patients whose diagnosis was made early enough have a good prognosis. Depending on the location of the cancer, survival after 5 years is estimated at 87% for breast cancer, 94% for prostate cancer and 63% for colorectal cancer. Before spreading to other organs, the primary tumor - in other words, the place where the cancer appears - can be eradicated by surgery followed by appropriate treatment (chemotherapy, hormone therapy, radiotherapy). However, when the tumor has spread to other organs, it can be more difficult to contain the disease. Metastatic cancer is a cancer located in one or more organs different from the original one. Thus, our body has more difficulty defending itself despite medical advances. One of the associated causes resides in the cells contained in metastases, containing genetic mutations that make them resistant to treatment.
The individual has a multitude of cells, constituting the various organs and other tissues of the human body. Cells are renewed every day: new cells are created and others die naturally. Cancer is the result of a series of dysfunctions within this cell renewal and takes place in 3 stages: - The first step is called initiation. In this stage, a cell in the body damages genes and produces genetic mutations. This phenomenon, which is quite common, generates several repair mechanisms for deoxyribonucleic acid (DNA), which guarantees the elimination of these mutations and allows the proper functioning of cell renewal. Despite defense mechanisms, some cells still fail to kill mutated cells and move on to the next step in the metastatic process. - The second step is promotion. During this stage, environmental factors stimulate the formation of cancer cells. The main factors are alcohol and tobacco consumption, poor diet, sun exposure and obesity. - Finally, the last step is that of tumor proliferation. In this stage, the cancer cells proliferate in an excessive and anarchic way to form the tumor. It is especially at this stage that the person experience the first signs of fatigue. Once the tumor process has started, it is therefore ideal to consult to be able to contain the disease. Otherwise, the process of tumor dissemination, also called metastatic process, starts.
Within tumors, there are cells called "Circulating Tumor Cells" (CTC), which manage to detach from the primary tumor. In tiny amount, they cross the wall of blood vessels and then circulate in the blood to an organ. If these cells are not eliminated by the body, they manage to form metastases. This mechanism involves the transformation of tumor cells from an epithelial nature, which have many junction molecules allowing them to group together in the form of a tumor, into mesenchymal cells which are themselves, independent, malleable, and mobile. Once these CTCs are able to colonize one or more distant organs, the opposite phenomenon occurs: the cells once again acquire their epithelial properties to form one or more new tumors.
Illustration of metastatic process (Photo credit : Alexandra Soler)
The formation of cancer is therefore a succession of events within our own cells, which can be amplified significantly by environmental factors. To date, many research teams are trying to find more effective treatments with new therapeutic targets such as gene therapy or immunotherapy. Other teams are focusing on new detection methods - and therapeutic monitoring - notably with CTCs, in order to obtain earlier detection of cancers and thus avoid any spread.