Cancer is caused by mutations to certain genes. When we get treatment we don't know if we kill or remove or completely treat the mecanism that caused the mutation in the first place. The mutation can be an DRIVER or a Tumor supressor or both. There are usually two invoved..
Then there are pathways involved with cancer..Some are more open in certain cancers.
In some cancers we do a better job than others because the line of mutations are not as complex.
I wish I could post a graf of the mutation lines to help explain. But for those cancers that we can cure there are just a few mutations and then they go up from there. Everyday headway is being made to better understandi the mutations and pathways. Really its going so fast every single day. Like dominos when a door open several more fall open as well.