Gelatinous carcinoma1 of the breast is a comparatively rare state. In a combined group of 2,944 carcinomas of the breast cited by Gaabe,2 49, or 1.66 per cent, were of the gelatinous type. Gelatinous carcinoma occurs in patients of about the same age as do the usual forms of carcinoma of the breast. Tumors undergoing gelatinous degeneration sometimes reach an enormous size and the mass of the tumor may consist largely of gelatinous material. On the other hand, the amount of gelatinous material may be so small that it may be readily overlooked. Similar degeneration is known to occur in tumors arising in other situations where mucin-forming cells abound, notably the large intestine, stomach and biliary tract. Gelatinous carcinoma of the breast exhibits characteristic gross and microscopic appearances. The gross features may be striking. Large or small areas of the tumor may be somewhat translucent in appearance and