I think that currently with these treatments complete remission is luck of the draw. Although many of these treatments (trastuzumab, cetuximab) were designed to block a growth factor from signalling on the cancer, what they ALSO seem to do is to recruit the immune system to the cancer and basically paint the cancer with a giant target.
Now, there is basically a competititon here; is your immune system powerful enough to kill the cancers painted by the antibodies faster than the cancer can adapt (usually by short-circuiting the growth signal). This sounds hokey, but for patients on these class of antibodies (ADCCs "antibody-directed, cell-mediated cytotoxicity"), I'd say it's important to keep a positive attitude, eliminate stress from one's life, and other things that strengthen the immune system. Unfortunately there are a lot of chemotherapeutics which are coadministered with these antibodies that throw a wrench into the immune system, as does radiation, etc.
As for the future, I think that there are some sneaky tricks that we can do to make ADCC drugs more powerful. Right now there is actually batch-to-batch variation in the power of these drugs, again going back to the 'luck of the draw'.
I also see some potential for ADC ("antibody-drug conjugate", not to be confused with ADCC) as well, this is attaching a warhead to an antibody and just directly killing the cells, although I think the ADCs that are being designed are not potent enough. But that is another story.
Finally, there will be a class of general chemotherapeutics that don't touch the immune system (I work on one through my nonprofit, there is one in Phase III - SJG-136) which I think will make for a nice 'sweeper' system to clean up any cells that have snuck out of whatever the antibody target is.
In short: I see a future where ADCCs are combined with ADCs and next-generation chemotherapeutics.
The other big challenge is that it's kind of very expensive to make antibody drugs. I think there are clever ways of bringing the cost down, and I might be working on that too.