Even though it is blocked right now, I would still like to “confess” that my original diagnosis for this case was “angiomyofibroblastoma”, based on the morphology posted on line. Here are my rationalizations for that diagnosis:

The tumor is small size (2 cm), well circumscribed, and not hypocellular as the aggressive angiomyxoma. It appears to be heterogeneous in cell distribution (clusters, cords and single cells) and in cell morphology (stellate, spindle and sometimes epithelioid), with areas relatively hypercellular and other areas more hyalinized/myxoid. The tumor cells in general are very bland. The vasculature is mainly capillaries to small vessels with perivascular hyalinization. There are clusters of epithelioid cells with eosinophilic cytoplasm (best viewed in slide 17 and others), resembling the epithelioid cells in angiomyofibroblastoma. These cells can be clustered around vessels or as nests or cords or single cells in hyalinized/myxoid stroma. Mast cells and chronic inflammation cells are present, while no apparent mitosis or necrosis identified.

But then additional photos were sent to me:

I have to say that these photos look a lot different from the photos posted on line. It has to be smooth muscle tumor based on this morphology (cellular long fascicles intersecting with each other and with thick eosinophilic cytoplasm). Looking back at the original photos, I realize that there might be focal areas with spindle fascicles (slide 14, 15), even though it was nothing close to these photos.

As to leiomyoma vs leiomyosarcoma, one will have to count the mitosis and maybe look for tumor necrosis and other features under microscope. A Ki67 stain could be helpful as well, especially when it is compared with nearby normal tissue (smooth muscle). I have to say that for myxoid or epithelioid smooth muscle tumors, one doesn't need that many mitoses to classify it as malignant.

After all, a good lesson to learn in this case is that one should analyze the entire case, not just selected areas.

Xlhong should be the winner. He/she already made the diagnosis of smooth muscle tumor from the very begining, while I didn't even consider it.