And this is not a joke, i will explain.
First, there's the issue of your level of immunity.
A strong immunity has probably slowed down the evolution of your cancer, but it will come in handy during treatment, in particular during chemotherapy.
The products that are going to be shoved down your system are targeting cancer cells, but not only (except in the case of very specific new types of treatments), and they are going to kill off also normal cells.
The evolution of your platelets, white cells, red cells and a few other indicators will decide whether you can qualify for your next chemo session.
If your white cells count drops too fast, you will not be able to keep up your schedule of chemo sessions, and you'll have to forgo one or more of them, to leave the body more time to recuperate and replenish its reserves.
A low count of white cells will also put you in danger of catching a cold, the flu or other illnesses, while you are undergoing your treatment; This can have known-off effects, as some of the drugs you may need to cure your infection may interact badly with some of the drugs that are in your chemo...
A low count in platelets will render you susceptible to cuts, and will hinder your ability to cicatrise quickly. Careful with this knife!
So, clearly, being in good shape before will increase your chances of finishing your chemo protocol on schedule, and, i can vouch that you'll be happy to avoid having a few more weeks of it, in the end.
It should also reduce your risk of developing too many of the usual side-effects, and if you do, they will be milder, and will disappear faster.
Another thing t take into account, if you already suffer from elevated blood pressure, chemo is going to be an issue.
Once they start pumping the various liquids in your body, they add codeine, some other anti-inflammatory products, on top of the chemo drugs mix. As a result, during the few hours of chemo, your blood pressure and pulse is controlled a few times, as it can rise by 20 to 40 points during treatment.
If you have 120/80, then it's fine, you may go up to 140 or 150, but what if your "normal" blood pressure is already 140? or your pulse is 80 at rest?
Lower data, indicating a good physical shape, will hold you avoid a thumping heart, or difficulty breathing during chemo.
For instance, my rest figures are around 105/60, with a pulse around 60. So i never even reached 140 as a maximum, and was able to pass peacefully the chemo sessions from beginning to end.
Finally, being in a good shape before surgery and chemotherapy will allow you to come back in shape faster, restart walking, running, going to the swimming pool etc. much faster, sometimes even while you're still under chemo, for instance, in my case, after 4 or 5 days and during the second week, before the next session.
IN con fusion, don't wait for a health scare to improve your health, do that on a regular basis so you're in a better situation in case you are hit with a serious illness, in particular cancer.