Brain Metastasis of Crystal-Deficient, CD68-Positive Alveolar Soft Part Sarcoma: Ultrastructural Features and Differential Diagnosis

ABSTRACT

We report a case of alveolar soft part sarcoma (ASPS) presenting as an isolated frontal lobe metastasis. The tumor demonstrated little or no immunoreactivity for a broad panel of antibodies yet strong, diffuse immunoreactivity with CD68. On electron microscopy, the characteristic rectangular to rhomboid crystalline inclusions of ASPS were not present. Electron-dense granules resembling peroxisomes were present, sometimes in association with elongated granular structures having a periodic, lattice-like arrangement. Metastatic ASPS was confirmed by demonstration of an ASPSCR1–TFE3 fusion and imaging studies that excluded metastatic Xp11.2 translocation renal cell carcinoma. The primary site was subsequently identified in the lower extremity.

• Alveolar soft part sarcoma
• brain metastasis
• CD68

ACKNOWLEDGEMENTS

We wish to thank Dr Alyaa Al-Ibraheemi, of the Department of Pathology and Laboratory Medicine at the University of Texas Health Science Center at Houston, for her assistance. Thanks to Drs Irina Vaysertreyger, Yuanyuan Zhang, and Xiao-qiong Liu of the University of Nebraska Medical Center for their technical assistance.

DECLARATION OF INTEREST

A.O. was supported by the National Institutes of Health/National Cancer Institute (Training Grant No. 5T32CA163185).