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We have studied 450 cases of human breast carcinoma at the histochemical and ultrastructural level. The breast biopsies were obtained from Canada, Mexico and Dominican Republic. This study was undertaken to evaluate the prognostic significance of classification of breast tumors, proposed in 1971 by Murad, based on their cell of origin. Under this classification, ATPase positive tumors represent those of myoepithelial origin, while the remainder are designated ductal or ductular based upon defined ultrastructural characteristics. We observed a distribution of tumor types essentially similar to that reported by Murad, and no significant differences were observed between the contributing centers. No correlation was observed between this classification and the histological classification described by Stewart. We found no evidence that ATPase positive tumors were myoepithelial in origin. They showed histochemical similarities to ductal and ductular tumors, and had features indicating their secretory nature. Estrogen receptor levels were measured in 20 cases, and did not reveal any correlation with tumor type. An interesting feature requiring further investigation was the high incidence of endocrine-like secretory granules in all histological types of tumors studied.

The extracellular components of small grayish-yellow atherosclerotic dots and streaks removed at necropsy from 17 human aortae not later than 3 hours postmortem, were examined with the electron microscope. The broadened intercellular spaces which separated widely the intimal cells contained in more superficial layers moderately to intensely electron dense, fibrillar and granular fibrin material and other blood proteins. Small osmiophilic bodies of different sizes and configuration were present in the deeper portions of earlier lesions and were more numerous in more advanced lesions. The latter contained less fibrin. In addition, myelin-like figures were often seen either “free” in the extracellular space or associated with degenerating elastic elements, remnants of fibrin, and with cellular membranes of intimal smooth muscle cells. These myelinated bodies possessed often a core of variable electron density and texture, but it was possible to identify the cores at times as shreds of elastic tissue, basement membrane-like substance, or remnants of fibrin. It is believed on the basis of the present studies that degeneration of elastica, insuded fibrin and detached basement membrane of smooth muschle cells as well as the many osmiophilic bodies interpreted as precipitated lipoproteins derived from blood, contribute to the presence of the extracellular fat.

Electron microscopic studies of foetal, neonatal and adult aortae in man show that elastic fibers and lamellae develop and “grow” by aggregation and fusion of single, characteristic elastic units. These units show a close relationship to the basement membrane of the smooth muscle cells in intima and media. “Micro-fibrils” of the extracellular space participate in the organization of the elastic units.