I think I have found a bug considering malignant cells... I had a malignant cell in play and my opponent poisoned it. I played an aflatoxin on it, so when it dies a new malignant cell should appear, but it didn't. (I was playing in trainer)
As far as I remember, when you aflatoxin any poisoned creature, if it dies, a malignant cell is created. I guess it should work on malignant cells themselves too, if you had that aflatoxin and could afford it.
Or maybe it is intentionally implemented, to prevent abusing aflatoxin?
I guess that would make sense, that malignant cells themselves are immune to aflatoxin, but it never hurts to ask if it is intentional, or a bug.