In an attempt to boost our natural immune response to cancer, some researchers have tried putting pieces of tumor proteins on tiny artificial particles and mixing them with immune system cells. When the immune cells come into contact with the particles, they ‘learn’ what tumors look like, so that they will seek out and attack tumors in the body. The technique sounds great in theory, but has been disappointing in practice so far. Now, new research shows that the shape of these artificial particles makes all the difference. The spherical particles that are typically used hardly touch immune system cells. But the overlap is far greater with elongated particles—and these also shrink tumors better. Spherical particles shrank melanomas in mice by 50%, while elongated particles shrank them by 75%. Even better, while none of the mice treated with spherical particles survived for a month, 25% of those treated with elongated particles did.