Tubular carcinoma: a variant of secretory breast carcinoma.

Fifteen cases of tubular carcinoma of the breast have been studied using histochemical methods for mucosubstances, immunocytochemical methods for casein and actin and conventional electron microscopy. Mucosubstances and casein were demonstrated lying freely in the lumina of the tubules. Occasionally, mucosubstances and casein assumed the form of target-like intracytoplasmic 'inclusions' like those characteristically seen in lobular carcinoma. The neoplastic cells did not react with antisera specific against actin. Even at ultrastructural level no myoepithelial cells were observed, whilst villi were revealed along the tubular luminal surface. It appears that, in addition to distinctive biological, histological and ultrastructural features, tubular carcinoma has an almost constant histochemical pattern. This suggests a differentiation towards epithelial secretory cells engaged in intensive milk protein production which has also been shown to be a feature of lobular carcinoma. It is concluded that though lobular carcinoma and tubular carcinoma of the breast have been traditionally regarded as two distinct entities, they have certain similar functional characteristics and it is postulated that these two tumours could represent the extreme variants fo the same entity: the infiltrative lobular carcinoma being the most undifferentiated and tubular carcinoma the most highly differentiated.