THE MAST CELLS 



connective tissues, invasion of normal tissues favouring the development of 

 mast cells, other mast cells arising as fresh connective tissue is laid down 

 within the tumour itself. 



2. Tumours rich in mast cells. Certain tumours appear to have a 

 characteristically high mast-cell content irrespective of the state of their stroma 

 or of the accumulation of mast cells at the periphery, though there is nothing 

 to suggest that the mast cells themselves are malignant. In view of what has 

 already been said concerning the normal habitat of the mast cell in relation to 

 fibrous tissue and blood vessels, it is not surprising to find the cells in simple 

 fibromas and angiomas (Baumer, 1896; Harris, 1900). Numerous mast cells 

 have also been observed in the skin lesions of neurofibromatosis (Unna, 1896; 

 Greggio, 1911 ; Cornil and Michon, 1924). 



So far as frankly malignant tumours are concerned Holmgren and Wohlfart 

 (1947) report an interesting experimental study of mast cells in chemically 

 induced fibrosarcomas in rats, the cells being numerous in fibroplastic tumours, 

 less common in more cellular growths. Within the substance of the tumours 

 the mast cells are scattered diffusely among the malignant fibroblasts, and though 

 the tumours are often rich in blood vessels, perivascular mast cells are compar- 

 atively rare. Serial transplantation of fibroplastic sarcoma rich in mast cells 

 led to the emergence of more cellular growths and, as this transition occurred, 

 the mast-cell content of the tumours declined. Other significant observations 

 in this study are first, that mast cells are always numerous at the periphery of 

 the tumours irrespective of their internal mast-cell content; secondly, that no 

 correlation whatsoever was seen between the density of the mast-cell population 

 and the presence or absence of 'free chromotrope substance' as described by 

 Sylven. Holmgren and Wohlfart conclude (p. 689) that 'the most likely 

 assumption appears to be that the mast cells develop locally in the connective 

 tissue of the tumours', a suggestion which is in line with the observations which 

 we have already made in our examination of the mast cell in chronic inflamma- 

 tion. I have confirmed many of the above findings in a series of uterine fibroids 

 and fibrosarcomas in women. 



Of great interest, therefore, are the non-fibroblastic tumours rich in mast 

 cells discovered in inbred mice by Bali and Furth (1949). The first is a trans- 

 plantable splenic tumour composed of polygonal epithelium-like cells 'thought 

 to be derivatives of splenic reticulum' and often containing erythropoietic foci 

 and large accumulations of mast cells. According to these authors (p. 607) 

 the mast cells were always numerous, 'in the "capsule" of the tumour and were 

 abundant about the connective tissue stroma and about the adventitia of 

 vessels', characteristics which the tumours retained on transplantation. It 

 is noteworthy that growth on transplantation was extremely slow, often 

 requiring up to six months for a nodule to become palpable. 



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