Alexander Lipschiitz 299 



coincident with those in our experimental guinea pigs (pi. 2, fig. 6).* The 

 microscopical structure of the experimental fibroid, though different from that 

 of the spontaneous fibroid of the woman or of the guinea pig itself (where 

 spontaneous fibroids are extremely rare: Lipschiitz"'"), differs also from ordi- 

 nary connective tissue in its abundance of cells, in the new formation of smooth 

 muscle fibers, and in the disorderly disposition of the collagen fibers. 



It might be argued that the definition of neoplasm or tumor which we have 

 given above does not cover our experimental abdominal fibroids. Indeed, the 

 experimental fibroid has no autonomous growth since when estrogens are 

 withdrawn, the fibroid begins to regress and when grafted beneath the skin 

 or into the abdominal cavity, the fibroid may resist for a certain time, but 

 eventually becomes absorbed. But if this precludes classification of the experi- 

 mental fibroid as a neoplasm, then neither is the uterine fibroid in ^somen a 

 neoplasm. 



III. Comparison of Estrogens and Carcinogenic Hydrocarbons 



The neoplasms produced by carcinogenic hydrocarbons in mice are unani- 

 mously recognized as comparable to spontaneous sarcoma and carcinoma in 

 man. This is appropriate, for they are structurally similar to spontaneous neo- 

 plasms and the induced sarcoma is transplantable. It has been reported that, 

 in the chicken, the induced sarcoma is even filtrable and leads to serological 

 changes similar to those reported with spontaneously occurring filtrable tu- 

 mors (Foulds"'). Can estrogens compete with these hydrocarbons as to their 

 tumorigenic powers? This is a delicate question which it would be vain to dis- 

 cuss at the moment. But we shall show below that there are similarities in the 

 conditions necessary for tumorigenesis from these two substances. f 



1. The Tumorigenic Minimum Quantity. The quantity of the carcinogenic 

 hydrocarbons which is still able to elicit a tumor (subsequently designated 

 as "tumorigenic minimum quantity") is certainly very small. Though experi- 

 mental data available are still insufficient, certain experiments show that a 

 single subcutaneous injection of 5 fig. (or less) of dibenzanthracene is suffi- 

 cient to elicit sarcoma in mice (Dobrovolskaja-Zavadskaja^). The same will 

 probably apply to other highly active carcinogenic hydrocarbons. It is gen- 

 erally asstmied that the tumorigenic minimimi for estrogens is very great. 

 Our own w^ork has, however, shown that this assumption is erroneous. It is 

 true that considerable quantities of the free hormone (estradiol or estrone) 

 must be injected in the course of a certain time to elicit uterine metaplasia; 

 but when esterified estradiol is used, the minimum quantity is much less. It 

 has been shown (Lipschiitz, Vargas, Jedlicky and Bellolio;" Bellolio") that 



* Sammartino and Gandolfo-Herrera^ observed two cases of tlioiacic fibroids in 27 animals 

 with abdominal tumors induced by estrogens. Lately a similar case was observed in this depart- 

 ment. It is the first among more than a thousand cases. This dilTercntial incidence of thoracic 

 fibroids in oiu" laboratory and in that of the Argentine workers may depend on the strains used. 



t The ideas here expressed were first presented in an address given to the Second Pan 

 American Congress of Endocrinology held in March, i()|i, in Montevideo. 



