Chinese medicine distinguishes every illness by nature, yin or yang, and by composition, depleting (draining) or repleting (filling). A yin—nature illness should be depleting, yang should be repleting.4 When a symptom corresponds to the nature and course of an illness. we say it “moves according to its proper course,” and it is not severe. When they fail to correspond we say the illness “moves contrary to its proper course.” and it will be severe.
Historical medical records show that cancer was rare and unusual. The first symptoms of simple bumps correspond to yin/depleting illnesses such as boils, which when drained cause some pain–sometimes requiring stitches to close the wound. When a cancer bump is opened, however, there is great pain. Inside are small holes which secrete large amounts of vile pus—conditions not evident of yin/ depleting illnesses. After the lesions are broken it is evident the illness is a yang/repleting one. This situation is contrary to the diagnosis prior to rupturing the boil and shows a significant “contrary” illness.
Now we understand some of the doubts and difficulties the physician encounters with this complicated illness. Dr. Yang showed great vision when he created the character for cancer. Cancer belongs to the yang/repleting variety and contains a suppressed energy. This energy is like a closed pot on the stove; when the heat is turned up too high, the fire is locked within, though the pot’s exterior may show no trace of the heat. If the physician can correctly diagnose the signals coming from inside, the nature and composition of the illness will be evident and its cure easier.
Summary: Externally yin and internally yang shows an illness proceeding contrary-wise. When a fire is suppressed inside, the body should not be cut open.
Q: After breaking, how do the nature and composition alter?
A: Exactly opposite—~the external becomes repleting and the internal becomes depleting.
source: Master of Five Excellences