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Presented by Dr. Pedram Argani and prepared by Dr. Katherine Fomchenko
This is middle-aged female with a history of breast cancer and a 2 cm renal mass.
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1. Question
This is a 50 year old female with a history of breast cancer and a 2 cm renal mass which was focally positive for actin and negative for estrogen receptor (ER), S100 and cytokeratin.
Correct
Answer: C. GLI1 rearranged neoplasm
Histologic Description: This is an unusual spindle cell lesion with a prominent myxoid stroma. The neoplastic cells are bland, and are separated from prominent vessels within the lesion by myxoid and variably hyalinized/fibrinous stroma. There are also large areas of hyalinization and calcification within the lesion which are paucicellular.
Differential Diagnosis: Metastatic breast carcinoma was a strong consideration given the history and the focal immunoreactivity for ER. However, this patient’s breast cancer was morphologically distinct from the current case, and was not spindled. Myoepithelioma was a significant consideration given the morphology and focal immunoreactivity for actin. However, the absence of cytokeratin immunoreactivity and absence of S100 protein labeling argue against that possibility. The morphology certainly raises the possibility of a schwannoma given the degenerative changes and spindle cell morphology. However, the absence of immunoreactivity for S100 excludes that possibility.
GLI1 rearranged neoplasms are particularly challenging diagnostically, in that they overlap significantly with lesions such as myoepithelioma, myoepithelial carcinoma, and ossifying fibromyxoid tumor. These neoplasms should be kept in mind when a tumor with this morphology does not fit entities such as myoepithelial neoplasm or ossifying fibromyxoid tumor by immunohistochemistry, and in such cases molecular studies are appropriate to establish a definitive diagnosis. This case demonstrated a GLI1-FOXO4 gene fusion by RNA-sequencing, and fits the spectrum of GLI1 rearranged neoplasms. Of note, GLI1 amplified neoplasms tend to have a more varied morphologic spectrum, perhaps due to amplification genes adjacent to GLI1.
Reference Am J Surg Pathol 2022; 46:667-687 (PMID: 34907995)
Incorrect
Answer: C. GLI1 rearranged neoplasm
Histologic Description: This is an unusual spindle cell lesion with a prominent myxoid stroma. The neoplastic cells are bland, and are separated from prominent vessels within the lesion by myxoid and variably hyalinized/fibrinous stroma. There are also large areas of hyalinization and calcification within the lesion which are paucicellular.
Differential Diagnosis: Metastatic breast carcinoma was a strong consideration given the history and the focal immunoreactivity for ER. However, this patient’s breast cancer was morphologically distinct from the current case, and was not spindled. Myoepithelioma was a significant consideration given the morphology and focal immunoreactivity for actin. However, the absence of cytokeratin immunoreactivity and absence of S100 protein labeling argue against that possibility. The morphology certainly raises the possibility of a schwannoma given the degenerative changes and spindle cell morphology. However, the absence of immunoreactivity for S100 excludes that possibility.
GLI1 rearranged neoplasms are particularly challenging diagnostically, in that they overlap significantly with lesions such as myoepithelioma, myoepithelial carcinoma, and ossifying fibromyxoid tumor. These neoplasms should be kept in mind when a tumor with this morphology does not fit entities such as myoepithelial neoplasm or ossifying fibromyxoid tumor by immunohistochemistry, and in such cases molecular studies are appropriate to establish a definitive diagnosis. This case demonstrated a GLI1-FOXO4 gene fusion by RNA-sequencing, and fits the spectrum of GLI1 rearranged neoplasms. Of note, GLI1 amplified neoplasms tend to have a more varied morphologic spectrum, perhaps due to amplification genes adjacent to GLI1.
Reference Am J Surg Pathol 2022; 46:667-687 (PMID: 34907995)
