Nonneoplastic endometrial signet-ring cells - Vacuolated decidual cells and stromal histiocytes mimicking adenocarcinoma

We describe 5 patients (mean age, 50 years; all had uterine bleeding) whose routine endometrial biopsy and curettage specimens contained prominent sig net-ring cells. Each specimen contained loose aggregates of signet-ring cel ls scattered within the endometrial stroma that were characterized by perip herally displaced small, uniform nuclei with indistinct nucleoli and showed no mitotic activity The central portion of the cytoplasm was occupied by s ingle or multiple cytoplasmic vacuoles. In all cases, the signet-ring cells were reactive for vimentin and negative for epithelial membrane antigen an d cytokeratin. Four cases were focally positive for muscle-specific actin o r smooth muscle actin and negative for CD68, Mac387, periodic acid-Schiff m ucicarmine, and alcian blue. In these 4 cases, the surrounding endometrial stroma showed decidual changes, and the signet-ring cells demonstrated a mo rphologic continuum with more typical decidualized stroma. As such, the sig net-ring cells in these cases were vacuolated, decidualized endometrial str omal cells. In the remaining case, the vacuolar contents of the signet-ring cells were periodic acid-Schiff-positive and resistant to diastase predige stion, and the cells reacted with Mac387 and CD68. The surrounding stroma s howed no decidual reaction. Thus, the signet-ring cells in this case were o f histiocytic differentiation Endometrial stroma occasionally may contain n onneoplastic signet-ring cells that closely mimic adenocarcinoma. At least 2 directions of differentiation, decidual and histiocytic, are possible.