Interrelated to Qi (Energy) in TCM are the substances Yin and Yang. Treatment, diagnosis and remedies can all be reduced to these two and their functions in the Body, Mind and Spirit of an individual. Some say no other knowledge is needed if you are able to properly understand Yin and Yang. It is said all else flows from them.
Western Medicine has no concept of Yin and Yang. However, it does consider cells and cellular life to be the cornerstone of all biological functioning, disease and treatment. If in TCM the core substances are Yin and Yang, in Western Medicine it is cells and cell life.