Biophysical studies of extracts of tissues of high- and low-breast-cancer-strain mice

Abstract

Electron micrographs prepared from extracts of normal and malignant tissues of 3 high-breast-cancer strains (C 3H, RIII, Strong A) of mice show the presence of approximately spherical particles of diameters ranging from about 200 Å to 1200 Å, though mostly not larger than about 300 Å. Similar micrographs from extracts of normal tissues and induced tumours of low-breast-cancer strains (C 57 black, CBA, IF) either do not show such particles or show them only occasionally. Extracts of RIII high-cancer-strain breast-tumour tissue show greater numbers of these particles than extracts of tumours from other high-breast-cancer strains. Electron micrographs of the extracts of breast tumours induced in C 3H high-breast-cancer strain males show smaller numbers of characteristic particles than those of spontaneous breast tumours arising in females of this strain. Electron micrographs of milk of C 3H high and C 57 black low-breast-cancer strains show similar numerical differences in the presence of the characteristic particles. Electron micrographs after ultracentrifugation of extracts from high-breast-cancer-strain tumours indicate that the particles are completely sedimented in two hours at a speed corresponding to 120,000 times gravity, but the critical speed has not yet been established. All extracts tested by the electron microscope and in the ultracentrifuge are being tested for the presence of the tumour-inducing agent by injecting them into C 57 × RIII susceptible hybrid mice; 56 out of 221 mice injected with extracts which contained the particles in large numbers have so far developed tumours. The relationship between these particles and the tumour-inducing factor is not yet clear. It is necessary to await the final results of the biological tests in hybrid mice before a definite correlation may be regarded as established.