Doctors use a range of ways of describing these stages. Usually, stage 0 is in situ cancer; stage 1 is localised cancer, although further local spread may take it to stage 2; stage 2 also usually includes spread to the nearest lymph nodes; stage 3 usually indicates more extensive lymph node involvement and stage 4 always indicates distant spread.
Stage is also very important to prognosis – prediction of the cancer’s effect on the person who has it. On average, the higher the stage, the worse the cancer’s effect on the person who has it. The hope of cancer treatment is that it will improve the prognosis, both in prediction and in reality.
Stage 0 - "In Situ"
A cell that becomes a cancer cell usually does so in the company of other similar cells. Often, but not always, it can produce a tumour right there in that tissue, in a way that poses little or no threat to life. This is called in situ cancer; that is, cancer in the position where it started. It is probable that some cancers never go beyond this early stage.
Stage 1 - Localised Cancer
At the next stage, the cancer cells gain the ability to pass through the ‘basement membrane’, that is the thin, fibrous boundary to the tissue in which the cancer began, and to invade neighbouring tissue. This invasion is a serious step, because it indicates that the growing cancer cells may threaten life.
While the cancer remains a single lump, partly in the tissue where it began and partly in a neighbouring tissue, it is said to be in the localised stage.
Stage 2 & 3 - Regional Spread
Once a cancer cell has invaded, a common next step is for one of its daughter cells to invade through a lymph vessel (a vessel like a blood vessel that carries the clear fluid called lymph, which is all the time exuding into tissue from our blood capillaries (the smallest blood vessels), back to the blood stream).
On the way to the blood stream, the cancer cell can get caught in a lymph node, one of the powerhouses of the body’s immune system. There it might provoke an immune response against it, which can go on to destroy it and the other cancer cells. Wonderful!
Sometimes, though, it divides and forms a lump in the lymph node. This stage is often referred to as regional spread. That is, the cancer has spread within the general region in which it first began but not to other parts of the body.
Stage 4 - Distant Spread
The next step can be quite varied. Cells from the lump in the lymph node may spread further through lymph vessels to more distant lymph nodes or on into the blood stream. Or cells from the original lump may invade a capillary and enter the blood stream that way.
Either way, once in the blood stream, the cancer cells can go just about anywhere in the body, form new colonies and spread further. This is the stage of distant spread.