Change of research field from physics to biology
There is absolutely a need for physical scientists in cell and developmental biology as well as cancer. Take a look at, e.g. this story: https://www.aps.org/publications/apsnews/201003/nih.cfm

I know many, many physicists who have moved into experimental biology, and PhD to postdoc is a natural time to do this. However, if you are going to need to be trained in a wet lab, you need to ensure you are moving into a group that values the other skills you bring - rigorous quantitative thinking, computational skills, spectroscopy or microscopy - enough to train you in the biological part.

How do you find these people? First, I'd suggest reading deeply in the field you'd like to go into, and seeing when people use ideas from physics (e.g. groups studying phase transitions in RNA granules, or collective behavior of cells, or entropy and information in developmental biology), or look at mechanics in detail. Those groups are more likely to be receptive to someone with your background. Other tell-tale signs are groups who are listed in "quantitative biology" programs or who are housed in Physics, Mechanical Engineering, Bioengineering, etc. If you are interested in cancer, places with Physical Sciences in Oncology centers are natural fits.

My impression is that, though there is a lot of competition for postdocs in biology, students with strong quantitative backgrounds who want to work in wet labs are hard to find.