Cancer: Introduction, Part I
It seems the initial cancer in the mucosa, therefore on the surface, can grow only in the superficial epithelial layers for some time, not infiltrating into the tissue beneath the mucous membrane (submucosa). The moment tumour starts to grow uniformly on all sides, just like the inflating rubber balloon gets bigger, we say that it grows expansively. All tumour cells remain together sticking tightly to the tumour’s matrix like some cohesive force is keeping them together in one place. The result is sharply circumscribed tissue separated from the surrounding tissue - the tumour node.
The tumour tissue pushes aside the surrounding tissue to create the necessary space for itself to grow. That pressure makes cells of the surrounding tissue to atrophy (decrease in size), and even sometimes to disappear. On the border between tumour tissue and healthy tissue there is a regularly formed layer of connective tissue that like the cocoon covers the tumour.
Benign tumours grow slowly and expansively. They are not life-threatening by themselves but if they are unfavourably situated, for example in or near the brain, they may indirectly cause death. They are relatively small in size, sharply separated from the environment. That kind of tumours "behaviour" allows to a surgeon to remove it completely without difficulty.
Invasively (infiltrative) growing are those tumours that penetrate into the tissue just like roots penetrate the soil when we are planting a plant. The phenomenon of separation allows tumour cells to separate from its base and move away from it, affecting the healthy surrounding tissue. A destructive growth is the end result of infiltrative growth. There's no destructive growth without infiltrative grow but there's infiltrative without destructive growth (some hemoblastosis - rapidly grow disorders of the blood-forming tissues).
Tumour has no its own vascular system (the vessels and tissue that carry or circulate fluids such as blood) or nervous system. It consists of two types of tissue: parenchyma (mutant cells), an essential part of the tumour, and stroma (a connective tissue that in interaction with tumour cells supports their growth). Certain types of skin cancers cannot spread throughout the body because the cancer cells require nearby stromal cells to continue their division. The loss of these stromal growth factors when the cancer moves throughout the body prevents the cancer from invading other organs.
It's often said that the tumour is mature (differentiated) or immature (undifferentiated, embryonic). The former means that the cells have completed development in a certain direction, and the later that they are on some lower level of the development.
Some malignant tumours (like glioblastoma, the most aggressive malignant primary brain tumour) can cause death within a few months, some in 1-2 years, while some tumours may be present in the body for several years, requiring no treatment other than periodical observations. "Spontaneous cures" are such rarities that it is the question whether spontaneously disappeared "malignant" tumour was cancer in the first place.
Malignant tumours grow rapidly, infiltrative and destructive in a chaotic manner. There are malignant tumours that remain small, not because they would grow slower but because their cells die and they are absorbed or shed from the tumour area. Finally, the organ in which malignant tumour grows, either primary or secondary, is so damaged that it cannot fulfill its functions or it shuts down completely.
By infiltrating and destructing the environment, cancer cells break through the wall of the blood and lymph vessels and start to spread cancer cells from the primary place of origin to other places in the body. Then we say cancer has metastasized.