Cytoplasmic non-epithelial mucin accumulation associated with CD44 in an astrocytic tumor with signet ring features

We report a case of an atypical astrocytic tumor rich in signet ring cells with cytoplasmic mucin and glycogen in the left lower temporal lobe of the brain found in a Japanese female tricenarian. The signet ring cell cytoplasm contained bovine testicular hyaluronidase sensitive non-epithelial mucin together with CD44 and laminin. Glycogen was also detected. After subtotal resection, the residual tumor rapidly enlarged; hence, it was finally extirpated 8 months later followed by post-surgical irradiation. The recurrent tumor did not have signet ring cells and was entirely comprised of solid nests of large pale polygonal cells filled with glycogen and hyperchromatic nuclei. Mucin was not demonstrated in their cytoplasm, but their surface was diffusely coated with non-epithelial mucin together with CD44. The results of our analysis revealed that non-epithelial mucin could accumulate in or on the surface of neoplastic astrocytes in close association with CD44, findings that give new insights into the spectrum of non-epithelial mucin metabolism in astrocytic tumors. The tumor has not recurred for more than 3 years after the irradiation therapy following the second surgery, but further clinical observation is needed to evaluate the exact clinical behavior of this unusual tumor.