>>13547184>DiabetesKeto diet literally solves this, your pancreas can and will recover if you cut out carbs for a while. Doesn't need to be permanent, just long enough to heal.
On the off chance someones pancreas is too far damaged for this, pancreatic cell, tissue or complete organ transfer would be the next best thing (or some sort of chemical/ therapy to induce regeneration in it). This will be in the 2nd half of the 21st century sometime.
>CancerWe've found many cures they all disappear or get disinfo'd. An 'official' cure I would predict 2nd half 21st century, and it'll be something patentable of course so pharma lot can make trillions from it.
>Brain disordersThis one is more complicated. If you mean neurological things like autism then those are linked to stunted nervous system development in the womb often due to toxins ingested by the mother (cigarettes, alcohol, drugs, medical drugs). You'd need to basically have some sort of regenerative effect on the nervous system/ brain & spinal tissue. I reckon medicine won't advance that much until sometime in the 22nd century, but mostly just because capitalism and greed holds it in the dark ages.