At 9:55pm,tuesday night, my female panchax died of tumor on her back and it spreaded to her side and crushed her lungs and heart.
Are tumors common in fish and how long does a tumor take to kill fish?
dont take this the wrong way - but are you a specialised fish pathologist, or is your diagnosis actually a guess? I'm guessing the later, by the rest of your question. Is this the same fish that was getting 'fat' and ready to breed?
I suggest its a bacterial infection - purely because a fish that gets 'fat' usually has this. Its also known as dropsy - and is usually incurable.
As a general rule, most animals are protected from infection by their immune systems. Usually pathogenic bacteria is all around them, and as long as they have clean water, good food, and a relaxed life they will do fine.
Your fish must have had something bothering it - to make it get ill. Possibly bad water, bullying tank mates, wrong food, wrong temperature, wrong water parameters, general stress, chemical stress from too many medications. Whatever was bothering this fish you need to fix it before other fish get stressed, then weak immune systems then sucumb. Is your filter ok?
Anyway, only you can say what thing(s) were stressing your fish, but I would think very carefully about what goes in your tank!
Anyway, panchax are very easy fish - sort out your tank, and try again!
