How does cancer spread and why is it deadly?

As explained in the question " What are malignant diseases (cancer) ? ", as a tumor mass grows, some cancer cells can "break off" and travel to distant parts of the body. This process is facilitated by the fact that practically all parts of the body are connected by small blood and lymph vessels, and it is through the blood or lymphatic system that tumor cells can reach distant parts of the body. Usually, in order to penetrate the bloodstream or lymph, cancer cells need to acquire additional mutations that give them this ability. By entering the bloodstream or lymph, tumor cells are again exposed to various dangers that can lead to their destruction, but if they survive, they can at some point leave the blood or lymphatic system again and remain in the tissue. Through further division, such cells can form new tumor masses far from the site of the primary tumor, which we call metastases. Metastases are therefore not new primary tumors , but direct descendants of the tumor mass from which they previously arose, so metastases are called primary tumors. For example, breast cancer that spreads to the lungs is called metastatic breast cancer, not lung cancer.

When viewed under a microscope, metastatic cells generally look the same as the cells in the primary tumor and often share many common molecular features, such as the presence of specific chromosome changes.

Slika 1. Illustration of a tumor cell entering the bloodstream. Such a cell can travel through the blood to distant parts of the body, and if not destroyed by the immune system, it can re-emerge into the tissue and form a metastatic focus.

Why is cancer a deadly disease? In addition to metastasizing, cancer cells can invade surrounding tissues and organs by direct spread. For example, a rectal tumor can directly invade the bladder. It is these two processes (metastasizing and direct invasion) that are largely responsible for the high mortality rate from cancer . The formation of metastases in other tissues and organs or their direct involvement can ultimately lead to the failure of one of the organ systems without which life is impossible (for example, the liver). Metastatic tumors can cause significant damage to the body's function, and most people who die from cancer die from metastatic disease. Some patients also die from the general effects of cancer on the body, such as cachexia (advanced stage of weight loss and muscle mass) and general fatigue, and some are unfortunately also triggered by the side effects of oncology therapy.

Additional interesting facts

The ability to metastasize is one of the basic characteristics of malignant tumors, which clearly distinguishes them from benign tumors. Although benign tumors can (although rarely) be life-threatening due to their location (for example, a benign brain tumor can press on surrounding nerve structures), these tumors never metastasize. On the other hand, all malignant tumors can metastasize , but the risk of metastasizing is not the same for all types of cancer. For example, basal cell skin cancer metastasizes extremely rarely, while it is a common occurrence in aggressive diseases such as lung or pancreatic cancer. Also, different types of tumors have different sites to which they spread . For example, colon cancer most often metastasizes to the liver and lungs.

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