So is the treatment something highly unusual?

I am sorry to be prying such information out of you, but things with such a cost label tend to be very high-tech (e.g. tumor-invading lymphocytes etc. that need to be cultivated for each patient separately, which cannot possibly be cheap).

It's a monoclonal antibody.

I suspect it'll look cheap in comparison to life extension treatments.

That's because monoclonal antibodies are targeted to a very specific protein. Polyclonal antibodies which can be used more generally are much cheaper. You're paying for the purity, not the substance.