Who gets which tumor and when is a complex process in which many factors interplay — genes, lifestyle, nutrition, etc.. (2ndchance.info)
The immune system is a complex system of molecules, cells and tissues responsible of combating external and internal insults. (research.hsr.it)
If your companion's problems are complex in nature, specialists may be consulted and transfer to a specialty service may be recommended. (cvm.ncsu.edu)