NEOPLASTIC ABNORMAL GROWTH 257 



the neoplasm only as composed of irreversibly altered constituents 

 which continue to reproduce themselves faithfully forever. Certainly 

 much evidence favors the view of permanent cellular change, but there 

 exist data which require the inclusion of an environmental factor to ex- 

 plain some neoplasms. Furthermore, all cancers need not arise and con- 

 tinue to grow because of exactly the same mechanism. Green (117) 

 has called attention to the fact that two neoplasms, histologically iden- 

 tical, may differ wholly in the degree to which they are autonomous. In 

 man, too many regressions of breast and prostate cancer occur to allow 

 the complete elimination of the general control of cellular environ- 

 mental factors as a possible participant in the neoplastic process. 



From the vast collection of factual material existent on neoplastic 

 growth, one fact in particular stands out as worthy of special mention. 

 This is that further data are urgently required on the comparative com- 

 positions of normal and neoplastic cells. These data may concern genes, 

 enzymes, proteins, or any other component. They may be derived from 

 direct analytical methods, from tracer studies, or from the different 

 susceptibilities of the two cell types to toxic agents. Precise informa- 

 tion of this type is likely to advance significantly our knowledge of the 

 problem, somewhat more than discussions of whether the etiologic 

 agent is a component foreign to the host or of host origin. It is impor- 

 tant to prove only that it is different from any normal component and 

 to learn how to accomplish its destruction. 



REFERENCES 



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3. Seidlin, S. N., and L. D. MarineUi. Therapeutic Effect of Radio- 

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4. Haddow, A. On Secondary Colony Development in Bacteria and an 

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5. Burrows, H. Biological Action of Sex Hormones. Cambridge Uni- 

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6. Allen, E., and W. U. Gardner. Cancer of Cervix of Uterus in Hybrid 

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