The likely reason the cancer is transmittable at all is due to underpopulation/genetic bottleneck. Animal immune systems usually have no problem recognizing and

The likely reason the cancer is transmittable at all is due to underpopulation/genetic bottleneck. Animal immune systems usually have no problem recognizing and destroying cells from other individuals, even cancerous ones, but you need sufficiently distinct immune markers on your cells for them to recognize as "foreign."