Why cancer cells are difficult to destroy?

When your body's cells replicate, they go through 3 phases. The first being the growth phase. The second being synthesis or replication of the DNA. The third being the phase where it checks over the replicated DNA to check for any errors (or spell check kind of). Cancer is when those body cells that are being replicated, are replicating way too fast for them to go through the 3rd phase and get checked for errors. Usually, when they are replicating this fast, there is some sort of mutation that is causing them to replicate this quickly.

When these cells skip the spell check, they have a mutation and this mutation causes the mutated DNA to take over all of the normal DNA. If the cancer is caught early enough, then there are technologies that can get rid of the small amount of mutated DNA but if noticed too late, the cancer cells have already taken over that persons body, and it would take some extensive treatment to even attempt to get rid of all the cancer cells..

Hopefully this helped answer your question. :)