SPONTANEOUS NEOPLASMS IN MICE 223 



the types of ovarian tumors found in mice subjected to x-rays and state that 

 spontaneous tumors of the ovaries are very rare (16). This last paper is 

 of interest to us in that we have observed, in our spontaneous tumors of the 

 ovaries, types that compare with most tumors which developed following 

 irradiation. 



Probably because of the complexity of the ovary it can be the primary 

 site of a fair number of tumors in some stocks of mice. This is true of the 

 ce (extreme dilution) stock in our laboratory. Scattered cases have been 

 found in several of the pure stocks. Also offspring of crosses between pure 

 stocks have developed several spontaneous tumors especially where the 

 C57 black mice have been crossed with the dba, A albinos and Mus bac- 

 trianus. Altogether we have found over 50 spontaneous ovarian tumors 

 in our mice. This does not include simple cysts which are common and are 

 not malignant. They are probably associated with abnormal physiology. 

 These cysts may be lined by a single layer of flattened or cuboidal epithelium 

 and occasionally are distended by hemorrhage into the cyst cavities. Those 

 lined by ciliated cuboidal epithelium arise from the vestigial tubules, the 

 epoophoron. 



Ovarian tumors in mice show considerable variation in appearance. The 

 majority of these tumors already observed would probably tit into one of 

 the following classes. No doubt additional forms will be found. 



A. Cystic tumors. 

 Papillary cyst adenoma. 

 Papillary cyst adenocarcinoma. 



B. Solid tumors. 

 Granulosa cell tumor. 

 Hemangioma. 

 Hemangio-endothelioma. 

 Fibroma. 

 Fibrosarcoma. 



C. Embryonal tumors. 

 Teratoma. 



Embryonal adenoma. 

 Embryonal cell carcinoma. 



Cystic tumors. — A cyst that grossly appears to be simple may contain 

 numerous small or large papillary ingrowths. These papillae may have 

 simple cuboidal or columnar epithelial cells covering their surfaces (Fig. 

 122). Such tumors are papillary cyst adenomas and are benign . A papillary 

 cyst adenocarcinoma may arise in the same manner. 



