When doctors tell a patient how long they have to live, it’s just a guess based on how long previous patients with the same disease at a similar stage have lived. But every patient is different, and various factors will affect exactly how long they live.
When doctors give a prognosis to people (that is, a diagnosis for the future), it is always an estimate based upon the history of the patient, their own medical experience and the currently available scientific knowledge. Prognoses which over- or under-estimate the amount of time left to a patient occur often – because it is not currently possible to measure to exact time until death!
If a doctor has said the patient will live for 4 months and they died in half that time, then the doctor was clearly unaware of the extent to which the cancer was affecting the patient. This can happen in the case where the cancer is highly progressed and has already spread elsewhere in the body – as doctors cannot necessarily know everywhere in the body the cancer cells have gone.
Any prognosis should be taken as a guide, and the margin of error should always be taken into account. To be honest, if I had brain cancer and I was told I had 4 months to live, I would take it as a sign that the cancer was in a developed stage, and I would take each day as it came.
Unfortunately it is really difficult to predict exactly how cancers will behave. What you describe might happen because the cells are increasing more rapidly than expected. It also might happen if the tumour caused damage to other parts of the body more quickly than was expected too.
Well, that is quite hard to answer. I think that doctors can only give you an estimate of how fast the cancer is growing and how much your body can cope with it, but it’s definitely not accurate. It’s also true that a lot of times they say that you have only few months, but then you can live longer than their prediction
It can be difficult to make an accurate prognosis. I belive they are made with statistical models, which can often be off by quite a long way. The reason could be because of the cells rapidly growing and dividing, or it could also be because the tumour is taking up a lot of nutrients from the blood supply, and there isn’t enough left for the patient, especially if they are weak. It might also be because the patient didn’t respond to therapy as expected – there can be quite a lot of variation between patients, even with the same type of cancer.