That's a terrible blow. We will pray for your brother this afternoon.
My children sometimes get miraculous results to their prayers:
Two weeks ago, my mother found a lump under her arm.
As she already has lung cancer, we all thought it was spreading:
Near the surface, the size of a pea, and hard.
She did an immediate Skype exam with her doctor, who broke into tears and told my mom to get right down to the hospital for MRI/CT/Xrays.
But when she got into the examination room, neither she, nor the doctors could find the lump which all had seen a couple hours before.
All the MRI's/Xrays/CT's revealed nothing (this is only 2 weeks ago), and we are all saying to ourselves, "Hmmm...."
A couple years prior, my wife's uncle was diagnosed with bladder cancer, told it was going to have to be removed, and he was going to have to use a side bag for emptying.
The kids prayed for him, and at his followup, there is no sign of any cancer at all. The Xrays/MRI's look like they are from two different people.
I believe the prayer of children, devout and simple, grabs Our Lord and Our Lady's ear.
In any case, you have our prayers, and I hope your brother will be OK.