So, my fiance is in medical school and we have been looking

I suspect that one needs some medical knowledge to evaluate the correct grammar for this sentence!

What is the intended meaning?
(1) If someone has a previous diagnosis of cancer, then develops back pain, assume it is just simple back pain until you can prove it is something worse (i.e. malignancy)?

(2) If someone has a previous diagnosis of cancer, then we should assume that they will have back pain if a malignancy develops?

I suspect that "secondary to" has some idiomatic usage unique to the medical community.


Until can also be a conjunction, i.e. when followed by some event:
He studied until the test began.
They danced until the neighbors complained.


Correct. Passive voice is acceptable, even if the "actor" is never named. For example:

The famous painting was stolen from the museum last night. (By someone...maybe we don't know whom...)
The dish should be served immediately being removed from the oven. (By the chef? By your mom? Maybe it doesn't matter...)