Multiple primary malignant tumors occurring in the same individual are comparatively rare. Götting1in over a thousand necropsies on malignant growths encountered only two cases; von Hansemann2in the same number of necropsies found five ; Redlich2in 507 cases had two ; Reichmann2in 711 cases also had two. Several writers look on these sporadic cases as purely accidental, while others, as Adami,3Wooley4and Williams,5attach considerable importance to them, especially in the further consideration of the nature and etiology of malignant tumors. In the vast majority of cases, single malignant tumors originate from a single type of tissue, that is (for example), the squamous epithelium, the low cuboidal cells of the mammary acini, or the connective tissue. Malignant tumors are rarely composed primarily of both a transformed epithelium and of a transformed mesoderm. Until 1901, Wells6found but three undoubted