The first artificial cancer in the internal organs of experimental animals.

In the world history of cancer research, three achievements in Japan were groundbreaking. First, in 1915, Katsusaburo Yamagiwa and Koichi Ichikawa induced skin cancer on the ears of rabbits by the repeated application of coal tar. This achievement was the world's first generation of artificial cancers in experimental animals. Second, in 1932, Takaoki Sasaki and Tomizo Yoshida observed liver cancer in rats fed on rice inoculated with ortho(o)-aminoazotoluene. This achievement was the first ever artificial cancer in the internal organs of experimental animals. Third, in 1967, Takashi Sugimura gave N-methyl-N'-nitro-N-nitrosoguanidine, a known chemical mutagen, to mice in drinking water and induced stomach cancer. This achievement was the first artificial production of stomach cancer and provided experimental evidence that cancer is a disease originated from DNA abnormalies. In commemoration of the publication of the 100th volume of the Proceedings of Japan Academy, Series B, from articles previously published in the Proceedings, two papers related to the achievements of Takaoki Sasaki have been selected and republished with this article.