I'm Alex, a genetics PhD at UCL researching cancer evolution. I made this 13-minute visual introduction to explain why a tumour behaves like an evolving population of cells.

An animated melanoma shows how different cell populations emerge and spread. The video then connects variation and selection with treatment resistance, using imatinib as one example.

The melanoma animation starts at 4:30 and the imatinib section at 8:55. References and qualifications to the simplified examples are in the video description.