An electron microscopic study of acute promyelocytic leukemia with chloroma.

Tumor forming acute promyelocytic leukemia (APL) is rare and only three cases have been documented. However, there are no reports on either the chloromatous character or electron microscopical analysis. The present paper dealt with a light, electron microscopic and histochemical study of the tumor of APL in a 55-year-old Japanese male. The tumors found in the anterior mediastinum and right lower extremity. He died from respiratory disturbance and hydrothorax due to obstruction of the pulmonary truncus by the mediastinal tumor. In electron microscopy, the tumor cells showed dilatation, colloracious pattern and honey-comb-like structure of rough endoplasmic reticula (RER) and parallel array-arrangement of smooth endoplasmic reticula (SER). These abnormalities of ER are the same as those recently recognized in leukemic cells in APL. Furthermore, the intercellular junctions composed of opposing dense patches of the cytoplasmic plasmalemma were frequently found between the more immature tumor cell of the mediastinum.