Could you elaborate as to why you believe that?
Having worked on both biological and physical simulations the limits from a ground-up perspective are quite similar. While there are no well-understood analytic forms to describe biological systems, unlike in quantum systems, the fundamentals of the problem are the same: we can't predict things because there are too many interactions to easily model.
There is a whole world of non-traditional techniques opening up with increases in computational capacity.
We also don't know to what extent quantum computation would aid predictive modeling of protein interactions. It's possible that there are no leaks at the classical level of abstraction as to hurt predictability. But the problem still remains that experiments to fix parameters are hurt by the fact that the system is changing under you and interacts in a complex way with its environment which can't be known ahead of time. So the computational complexity is not necessarily easier (in a practical sense) even if we assume that there is no utility in modeling quantum effects.
One very theoretical idea of solving cancer (per cancer) would involve searching for a 'problem', an insult, outside of the learnability class of evolution which also does not harm healthy cells. This is computationally likely harder than BQP. Anything less, even if equipped with a quantum computer, would be evolved out of and with any survivors less attackable. Any way you look at it, it is a far harder problem than working out fission.
A population of cells is more complex than an atom as it requires more parameters to be fully specified. It is also harder to predict because there are several levels of non-linear feedback interactions within an environment that can never be fully given ahead of time. A population of cancerous cells is more complex than a population of cells because their dynamics are not stationary in time. Unlike a typical population of healthy cells, cancerous ones are able to, in effect learn and more effectively than even the immune system. Extend this to the full class of cancers to see why a simple mathematical theory of the kind we find in atomic physics is highly implausible.
As such, we have an object of higher descriptive and predictive complexity than atomic physics. Searching for this theory will take longer and is much, much more difficult in a formal sense.