Breast cancer is called ''Ruyan'' in literature of traditional Chinese medicine. We synthesized the ancient and contemporary discussions and raised the theory that ''Duxie'' (poisonous pathogenic factor) is the etiological factor and pathologic product through the whole course of breast cancer. ''Liuyin Fudu'' (latent poison of six exogenous pathogenic factors) and ''Qiqing Yudu'' (stagnant poison of seven emotions) are the main etiological factors affecting the breast cancer occurrence. ''Aidu Neisheng'' (internal product of cancer poison) is the essential change in breast cancer occurrence. ''Tandu Yujie'' (stagnation of phlegm, poison and blood stasis) is the essential pathogenesis of the breast cancer's development. ''Yudu Weiqing'' (vestigial poison) is the main pathogenesis of breast cancer after operation. ''Yudu Pangcuan'' (vestigial poison invasion elsewhere) is the key pathogenesis of recurrence and metastasis after operation. ''Sanjie Jiedu'' (dispersing accumulation and detoxification) is an important therapeutic principle in breast cancer's treatment after operation. The ''Tandu-Yujie'' pathogenesis theory and ''Sanjie Jiedu'' therapeutic principle developed the theory about breast cancer in traditional Chinese medicine, and have some clinical application value.

Key words: breast cancer, pathogenesis, traditional Chinese medicine