CARCINOGENESIS 



irrevocably lost in the cells of row 2 — a defect which is heritable. 

 This is indicated by the large cross covering the system involved. 

 As will be described later, some ancillary reactions of the altered 

 pattern may persist temporarily, as indicated by the short 

 arrows pointing away from the crossed circles. The initial 

 alteration may be either nuclear or cytoplasmic in origin. 



Although the heritable alterations in cells U, V, and W 

 affect some specialized function, it will be noted that a different 

 function is altered in each cell depicted. On closer scrutiny it is 

 evident that the future course of the cells is determined by the 

 particular system which has been altered. If the special func- 

 tion is one of the last to develop, as depicted by function H in 

 cell U, most of the remaining specialized functions are un- 

 altered, the general cellular economy experiences little change, 

 and the cell represents the type destined to give rise to benign 

 tumor cells. However, if the altered special function occupies a 

 more dominant position in the economy of the cell, as depicted 

 by the circle labeled L in cell V, some other functions of the 

 cell will be secondarily involved, and the result is a cell capable 

 of producing cells of intermediate malignancy. When the 

 altered function occupies a key position in relation to other 

 special functions, as represented by function S in cell W, many of 

 the other specialized functions will be secondarily disturbed. 

 Such a cell is potentially capable of forming a highly anaplastic 

 neoplasm. Since each cell has an abundance of many special 

 functions, it becomes obvious that almost any variation of cell 

 type is possible. Indeed, it is fortuitous for any two tumors to be 

 exactly alike when one considers the variety of combinations 

 that can result when one or more functions are altered simul- 

 taneously or sequentially. Defects in special functions may be 

 induced by carcinogens in any stage of normal development 

 such as cells B, C, D, or E, but neoplastic cells can never result 

 from cell E because there is no mechanism for transmitting the 

 change. 



It is also obvious that carcinogens produce a variety of bio- 

 chemical lesions which are not heritable. The cell may recover 



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