[rodoxcasta]

They focus the immune system on the tumor by teaching it to identify some "neoantigens" in the tumor. Turns out that tumors express various strange proteins in their cell wall, I suppose because of the inherent genetic instability.

Anyone know why this can't be a silver bullet for most tumors? Like, a way to target an intrinsic characteristic of cancers that in theory could be very effective on most of them.. sounds too good to be true. So, what's the catch?

[chrisamiller]

It's true that the whole problem of cancer therapy is "how do I target these cells over here, while avoiding the rest of your healthy cells, when they look mostly the same" And you're right that this is a really exciting and promising approach!

A partial list of the "catches" at present are

1) tumors are really good at down-regulating the immune system. If they weren't, they would have been cleared already

2) we're still fairly bad at knowing which of the many mutations in a tumor are going to be good neoantigens - that is, which ones the immune system will be good at recognizing and ramping up against

3) It's expensive to design personalized therapies for every patient, but may be necessary (see some of my other comments below)

4) Tumors aren't single cells, they're collections of them that can have different characteristics. Just like with other therapies, sometimes immunotherapies kill 99% of the tumor, but leave that 1% to come roaring back. (same idea as antibiotic resistance)

So yeah, lots of hurdles to overcome, but overall, I'm genuinely excited about the rapid progress we're making in the area of immunotherapies. It's impossible to overstate the effect that sustained research funding has had on the rate of advances in this field.

[bglazer]

There are various strategies that cancer cells can use to evade the immune system. They can simply stop expressing the neoantigen. Also tumor cells can express proteins that suppress immune cells.

The genetic instability works both ways, the weird neoantigens sometimes get expressed but theres so much heterogeneity in some tumors that the immune resistant cells can get selected for very quickly.