Treatment of breast cancer was the life work of Seishu Hanaoka (1760-1836) and one of his greatest achievements was the development of an oral general anesthetic called "Mafutsu-san." His intense concern about the disease drove him to develop the anesthetic. This is substantiated by the facts that the first administration of the anesthetic was a patient named Kan Aiya for a tumor excision of her left breast in October 13th, 1804, and the 154 patients with breast cancer were listed in the "Nyugan Seimei Roku" or "A Name List of Breast Cancer Patients." Thus the study of his breast cancer patients is essential and indispensable for understanding Seishu Hanaoka's medical biography in depth. However, the descriptions of names, dates and addresses of the patients written in "Nyugan Seimei Roku" are incorrect and they do not always agree with those in other historical documents. We also do not know whether the dates mean those of the first examination or those of surgical operations. Several case records of breast cancer patients described by his disciples have become available, and by comparing them with "Nyugan Seimei Roku," we could know more detailed and correct conditions of the patients. The case of the wife of Teiseki Matsubara is a typical one, in which the exact date and the cause of her death were eluciated.