Ultrastructural characteristics and variations in human mucinous breast carcinomas.

Nineteen human mucinous breast carcinomas have been studied by electron microscopy in order to investigate the variations in the fine structure of this type of tumor. All the investigated tumors are characterized by a well-developed, rough endoplasmic reticulum and prominent Golgi complexes. The majority of tumor cells contain secretory granules. Approximately 50% (9/19) of the tumors have cytoplasmic dense core granules that are morphological identical to the neurosecretory granules found in APUD-cell derived tumors. Six out of the nine tumors react positively in a Grimelius staining for light microscopic argyrophilic granules. Two of the investigated breast carcinomas contain tonofilaments that are normally regarded as characteristic of squamous epithelium. It is concluded that mucinous breast carcinomas--that to this time have been regarded as a morphological homogenous group of tumors--are ultrastructurally characterized by heterogeneity.