Ultrastructural aspects of mucinous (colloid) breast carcinoma.

Seven cases of mucinous (colloid) breast carcinoma were studied by electron microscopy. In addition to the predictably abundant mucosubstance production, the following observations merit elaboration: 1) absence of myoepithelial differentiation and basal lamina deposition, 2) notably developed cytoplasmic filamentous systems and relatively scarce lysosomes, 3) frequent and apparently well-developed intercellular junctions, and 4) a distinct paucity of vessels in the tumors' stroma. The rather favorable clinical prognosis of mucinous breast carcinoma despite the absence of myoepithelial differentiation and basal lamina deposition parallel observations made on medullary and tubular breast carcinomas, thus confirming that those parameters, however important, are not the sole determinants of an aggresive behavior. The conspicuous cytoplasmic filaments appear to be neither true myoepithelial filaments or tonfilaments. The peculiar arrangement of these contractile proteins and the suspected sarcity of lysosomal collagenases may be reflected in the rather low invasiveness of these carcinomas. Another factor that may impact favorably on the cohesiveness of these neoplastic cell clusters is the presence of abundant and well-developed intercellular junctions. We further speculate that the paucity of stromal vessels in these neoplasms may be the result of as yet unidentified factors that might inhibit angiogenesis.