98 Inside the Living Cell 



However, chemical poisons are not the only agents which cause 

 cancers. It was found by Dr Oppenheimer that if plastic substances 

 are embedded in the skin of an animal, a cancerous growth may be 

 formed. The nature of the plastic seems to be quite unimportant, 

 but if the plastic film is pierced with holes, no cancer may occur. It 

 seems, therefore, that the cancerous growth is due to interference with 

 the flow of oxygen and food materials and to the effort of the cells to 

 improvise an alternative way of living. 



Cancers may also be formed by continual irritation of a tissue 

 or if a wound is prevented from healing. It is possible that hp cancers 

 caused by contact with pipe stems are due to this, but chemical 

 action by tobacco tar is also a possibility. 



(4) Cancer due to Hormonal Disturbances. Somewhat similar in 

 origin are cancers due to hormonal disturbances, which are common 

 in older men and women. Many bodily processes, as we have seen, 

 are controlled by hormones and require an accurate balance of 

 hormonal actions, if they are to function properly. We have also 

 seen that the glands which produce hormones are themselves con- 

 trolled by other glands, such as the pituitary. In ageing individuals, 

 the proper balance of hormones may be upset and an abnormal 

 growth of glands may occur, either by overstimulation or because 

 the gland is making an effort to produce sufficient quantities of a 

 hormone which are required. 



Mammary cancers are very common in certain strains of female 

 mice, but removal of the ovaries reduces the incidence of the mam- 

 mary tumours. It follows that some substance produced in the 

 ovaries stimulates the occurrence of mammary tumours. In the same 

 way, breast cancer of women is sometimes successfully treated by 

 removal of the ovaries; similarly tumours of the prostate gland of 

 males is sometimes treated by castration. It is found that much can 

 be done in cases in which tumours are the result of the hormonal (or 

 endocrine) system being out of balance by restoring the balance by 

 suitable hormone therapy. 



It has also been possible to replace hormones by the synthetic 

 equivalent. In fact, one of the most successful chemical treatments 

 of cancer is by the synthetic oestrogens (see p. 166) used for cancers 

 of the breast and the prostate. 



CONCLUSIONS 



It will be obvious that the subject of cancer is a large and very 

 complex one and there are many different facets to the whole problem. 

 It is quite possible that cancer is not one phenomenon but many. 



