MYXOMA OF THE BREAST - REPORT OF A CASE WITH UNIQUE HISTOLOGICAL AND IMMUNOHISTOCHEMICAL APPEARANCES

A case of myxoma of the breast is reported. The patient, a 19 year old Japanese woman, showed a lump in the left breast which had enlarged g radually over 3 years. A tumor measuring 5 x 5 x 4.5 cm was located ma inly in the mammary parenchyma, but partially involved the overlying s ubcutaneous tissue. Histologically the tumor was multinodular and each nodule consisted of an abundant myxoid substance with a few spindle o r stellate mesenchymal cells. The presence of hyaluronic acid was obse rved in the myxoid area, and a few constituent cells showed immunoreac tivities for S-100 protein and alpha1-antichymotrypsin. Electron micro scopic studies revealed that some constituent cells looked like undiff erentiated mesenchymal cells, while others showed a differentiation si milar to fibroblast or histiocyte. These findings suggest that the con stituent cells might derive from totipotential primitive mesenchymal c ells.