Figure 1

Case 9. (a) Low magnification of an area in which most of the neoplastic cells exhibit prominent signet-ring-like features. (b) Higher magnification that better demonstrates the morphologic features of the signet-ring cells. The nuclei are often crescent shaped, hyperpycnotic, and located at the periphery of the cells. Case 11. (c) Low magnification of a lymph node involved by metastatic mesothelioma in which many of the neoplastic cells present signet-ring features. (d) Higher magnification in which many of the neoplastic cells exhibit early vacuolization that appears to progress to larger vacuoles. (e) Another area of the same case in which some of the signet-ring-like cells appear to be binucleated (inset) or forming tubular-like structures exhibiting peripherally located, hyperpycnotic nuclei (upper left and right). (f) In this area, the lumens of the signet-ring-like cells and the tubular-like structures contain abundant, flocculent, granular material, most probably proteoglycans, which could potentially be mistaken for mucin. Case 2. (g) Low magnification of an area in which the signet-ring-like cells appear to coalesce forming larger vacuoles that somewhat resemble fat cells. (h) Higher magnification showing some of the larger vacuoles separated by thin septa.