Tumours (lumps) can be benign or cancerous (malignant). Benign means it is not cancer. Benign tumours are made up of cells that are quite similar to normal cells. To start with, cancer cells stay within the body tissue from which they have developed – for example, the lining of the bladder or the breast ducts. Doctors call this superficial cancer growth or carcinoma in situ. The cancer cells grow and divide to create more cells and will eventually form a tumour. A tumour may contain millions of cancer cells. All body tissues have a layer (a membrane) that keeps the cells of that tissue inside. This is the basement membrane. Cancer cells can break through this membrane. If this happens, the cancer is called invasive.
Many of the commonly used cancer treatments, such as radiation or chemotherapy, kill tumour cells. But sometimes, after those cells have died and been cleared away, a tumour will respond by growing faster and more aggressively. And scientists don’t have an answer to why this happens. However, using computer modelling techniques, researchers at Northeastern University may have found the answer. Not all cancerous cells will grow into a tumour. The model showed that if a cancerous cell was rapidly surrounded by healthy cells, it was usually rendered inert, having no space to divide. If, on the other hand, a cancerous cell had open space to grow into, it was much more likely to evolve into a full-blown tumour.
So now the question is why don’t all tumours aggressively regrow after radiation or chemotherapy? Researchers have found that the answer lies with the maturity of the tissue the cancer is growing in. If chemotherapy or radiation kills tumour cells in an environment where there are more young cells than older cells, the healthy cells can out-pace and smother the cancerous cells. However, this is just a theory and if it can be confirmed with experimental research, it can help shape cancer treatments in the future.