690 



Cancer Research 



fishes, taxonomically and geographically separated. 

 For example, epithelioma of the lip has been re- 

 ported in both salt and fresh water fishes; among 

 the catfish in the streams of Pennsylvania (122, 

 136), the barbels in German rivers (97), the tench 

 in a German pond (47), the eels from the brooks 

 and coastal waters of France (217), the stints from 

 the brackish water of the Jasmunder Bay on the 

 Baltic Sea (16), the coalfish in the North Atlantic 

 (228) , and the croakers from the South Atlantic ( 7 ) . 



On the contrary, a single species may be affected 

 by a variety of tumors in different organs. For ex- 

 ample, in the pike, Esox lucius, tumors have been 

 obaiNved in the bones, muscle, subcutaneous tissue, 

 dental structures, ovary, kidney and thyroid; the 

 tumors include osteomas, osteosarcomas, fibrosar- 

 comas, lipomas, adenocarcinomas and lymphosar- 

 comas. 



For convenience of reference, all tumor-bearing 

 fishes of which we were able to find records in the 

 literature, or which we have ourselves observed, 

 have been assembled in Table 21. The classification 

 of the fishes is one used by most ichthyologists.* 

 The table is arranged according to orders, families 

 and species of fishes, variety and site of tumor, 

 author and date of publication. Only the zoological 

 names are given; the common names may readily 

 be found by referring to the tables of the various 

 tumors. Inspection of Table 21 shows at once the 

 great preponderance of tumor-bearing bony fishes 

 over cartilagenous fishes; thb may be readily ac- 

 counted for by the numerical superiority and greater 

 economic importance of the former group. Among 

 the bony fishes, nearly one-half of all species affected 

 are representatives of only S families, namely the 

 salmoids (Saimomdae — salmon, trout), the cypri- 

 noids (Cyprinidae — carp, dace, minnows, chubs, 

 barbeb), the codfishes (Gadidae), the flatfishes 

 {Bothidae), and the flounders (Pleuronectidae) . 

 Members of these families are not likely to be more 

 soaceptible to neoplastic growth than other species; 

 rather they are caught in vast numbers for food and 

 hence more often examined. 



II. TUMORS OF AMPHIBIANS 



Nearly all amphibians belong to one of two or- 

 ders: the Urodeles which retain their taik through- 

 out life stich as the salamanders, and the Anura 



* We are gnUcfal (or advice on this and other matters 

 concerning ckaUkation and nonoendature to Dr. Carl L. 

 ilubbs of the Scrtppt Institutbn of Oonaograi^y and Dr. 

 Robert R. Miller of the National MttMnn. 



which are tailed only in the larval stage (frogs, 

 toads). Although frogs and salamanders have been 

 used in laboratories throughout the world for a 

 century, remarkably few tumors have been reported 

 in these animals, perhaps because they have not 

 been looked for by investigators interested in on- 

 cology. There is no good reason for believing that 

 amphibians are less susceptible to neoplastic growth 

 than fishes or other vertebrates. For example, sys- 

 tematic search for tumors in one species of the com- 

 mon laboratory frog, Rana pipiens, has revealed that 

 these animals are commonly affected with adeno- 

 carcinoma of the kidney. 



URODELES 



In the literature there are only 7 reports dealing 

 with spontaneous tumors in urodeles (Table 21). 

 The recorded tumors comprise carcinomas in 3 ^)e- 

 cies, fibromas in 2, and melanomas in one species. 

 This apparent rarity of tumors in urodeles is the 

 more surprising since these animals, above all other 

 vertebrates, have retained the capacity to regenerate 

 complex tissues such as leg, tail and lens. Various 

 "explanations" have been offered, but none appear 

 biologically sound. It has been suggested, for ex- 

 ample, that the ability of the salamander to regener- 

 ate lost limbs is evidence of the retention into adult 

 life of such highly potent morphogenetic fields that 

 an aberrant cell will be forced to differentiate by the 

 organizer effect of the adjacent tissues and hence 

 uncontrolled growth cannot occur. The failure of 

 carcinogens to evoke a neoplastic response similar 

 to that observed in mammals has been interpreted 

 by some as evidence that urodeles are more resistant 

 to tumor growth than are other classes of verte- 

 brates. But as stated above the probability is great 

 that tumors are not as rare as they seem to be in 

 these animals; they simply have not been sought, 

 hence have not been found. 



Perhaps because of the paucity of spontaneous tu- 

 mors, few experimental studies of neoplasia have 

 been carried out on these animals. They have been 

 limited largely to attempts at the production of 

 tumors by means of carcinogenic agents, as in the ex- 

 periments by Martella (132), Koch and his associ- 

 ates (99), Fedotov (46), Finkelstein (51), Shev- 

 chenko (186) and Tokin (218). Other experi- 

 mental studies are those of the Champys (28) (ma 

 transmissible epithelioma in the newt, believed to be 

 caused by a virus, and the work of the Brunsts 

 ( 186a) on melanomas of the axolotl which probably 

 arise on a hereditary basis. A detailed account of 

 these various exi>erimenLs is given elsewhere ( I23a). 



