Long post, because apparently many neither understand nor appreciate the intricacies of cancer research and think that pharmaceutical companies and regulators are holding back cures. Your immune system is constantly surveilling your body for both self and non-self recognition. It does this by checking the proteins expressed. If it finds something it doesn't recognize, it ramps up the inflammatory response and attacks. If it is actually non-self, great. If it is actual-self, that is autoimmune disease. Cancer occurs when cells acquire mutations that both 1) alter cell division and 2) cloak those cells from recognition by the immune system. If the second part doesn't occur, then the immune system will recognize that something is wrong and kill the tumor when it's just a few cells. At a high level, many modern cancer therapies are about getting the immune system to recognize the tumor and do all the work on killing it. And yes, it's quite easy to do this. But this is where the "safe and effective" line comes in. If you're treatment just cranks up the immune response in general, you start killing the tumor AND other things. If you give me a decent CAR-T at work, I have tools to boost it in ways that'll eliminate any realistic sized mouse tumor in 24-48 hours. The problem is that it's just a general immune overdrive and the cells start attacking everything. Okay, let's not send the immune system into a frenzy and just use the CAR-T, which is a T cell that has been edited with a protein that we know binds to a protein that the cancer expresses. The hope is, if the cancer cells express X and we edit the T cells to explain anti-X, then they'll go and attack the tumor. But this is where specificity and selectively come in. Your body expresses thousands of different proteins. Sometimes they look very much like each other even if they are different. Say there is a protein called XX expressed in your heart, it shares 99.9% homology (likeness) with X. We inject X-CAR-T cells, they go and kill the tumor, everything looks great. But a few binded to XX in the heart and started inflamming the heart wall. Not good to the point of unacceptability. ...