Sure, but my point is that convergent selective pressure across different individuals' tumors is strong enough that they independently arrive on the same resistance mechanisms to a given therapy, e.g. [0]. Just like if you performed the same bacterial antibiotic resistance experiment [1] across multiple independent trials, you'd repeatedly get the same result.
[0] https://pmc.ncbi.nlm.nih.gov/articles/PMC2538882/
[1] https://news.ycombinator.com/item?id=48505231#48507925