The possibility that MMMF cause cancer in humans was raised by the finding that the experimental introduction of such fibre in a variety of forms into the pleural cavity or peritoneal cavity produced mesothelioma in several rodent species. Unlike asbestos, MMMF have not induced lung cancer or mesothelioma on intratracheal instillation or inhalation with two singular exceptions. These exceptions consist of an experiment involving ceramic fibre which is more durable than other vitreous fibres and another experiment in which lung cancer, mesothelioma and chest-wall sarcoma were produced by repeated intratracheal instillation of glass fibre in hamsters. It is suggested that the strikingly lesser tendency of MMMF to induce malignant tumours when introduced into the lung experimentally may be determined by its lesser degree of fibrogenicity, fibrosis being a precondition for the development of malignant tumours induced by fibres; also that fibrogenicity, in turn, is determined by fibre dimension, by physico-chemical characteristics of fibre and by durability. Inhalation of MMMF in man may not produce the scarred lung and pleura which must precede the development of carcinoma and mesothelioma. The introduction of a mass of fibrous material of any composition into the relatively sheltered confines of the pleural cavity where it becomes encapsulated and gives rise to tumours is not a significant test of the hazards of inhaled materials to humans.
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Marvin Kuschner (1987) studied this question.