The case of invasive lobular carcinoma of the breast which appeared in ascites, which was indistinguishable from reactive mesothelial cell.

A 74-year-old wolnan was admitted becase of a large amount of ascites. The patient also pointed out the presence of a breast tumor. Aspiration cytology of the breast tumor and a cytology exalnination of the ascites were pcrformed.Cytologicaly, the tumor cells in the ascites were small. sized and uniform-In celis with a low N/C ratio, the chromatin pat. tern was fine and uniform. ICL was observed in the cytoplasm. The tulnor cells were individually dispersed.The cytological findings strongly suggested that these cells were reactive mesothelial cells.Histologlcally, the breast tumor was diagnosed as an invasive lobular carcinoma that was positive for CA19-9. The peritoneum biopsy was diagnosed as a metastasis of the invasive lobular carcinoma of the breast. Thus, the cells which had been regarded as reactivc mesothelial cells were in fact adenocarcinoma cells.