Again, it's the only PI3K inhibitor which readily crosses the BBB.
Many drugs cross the BBB. And some of those that don't can be formulated as a nasal spray which bypasses the BBB.
As far as cancer therapies that can cross the BBB go, off the top of my head:
Temozolomide, the only current FDA-approved drug for GBM, readily crosses the BBB.
Kintara Therapeutics' VAL-083, the other drug currently in the GBM AGILE study, readily crosses the BBB. Their drug looks very promising, just like Pax.
Both PAT-DX1 and PAT-DX3 being developed by Patrys (ASX : PAB) readily cross the BBB. They are also considering the possibilities of using those assets to transport other drugs across the BBB.
Still, PI3K is a highly validated target and the fact that KZA has the only PI3K inhibitor which crosses the BBB is exciting.