Gastrointestinal stromal tumors with prominent signet-ring cell features.

Three cases of gastrointestinal stromal tumors characterized by a population of cells displaying prominent signet-ring cell features are described. The tumors occurred in women aged 45 to 74 years and presented as small (< 2.5 cm), well-circumscribed, serosal nodules located within the wall of the stomach, small bowel, and rectum. Histologically, the lesions were characterized by a proliferation of large, round-to-oval cells containing abundant clear cytoplasm with displacement of the nuclei toward the periphery, which imparted to them a striking signet-ring cell configuration. In some areas, the signet-ring cells were seen to merge with short fascicles of spindle cells, whereas in other areas, the tumor cells were associated with prominent deposition of myxoid matrix. Histochemical studies showed glycogen granules within the cytoplasm of the tumor cells in two cases. Immunohistochemical studies showed a heterogeneous pattern of staining, with strong positivity for actin, vimentin, and CD34 in one case; strong vimentin and S-100 protein and weak, focal positivity for actin and CD34 in another; and vimentin positivity alone in the third. The present cases illustrate an unusual morphologic appearance of gastrointestinal stromal tumors that should be distinguished from primary and metastatic mucin-secreting carcinoma and other types of neoplasms with clear cell or signet-ring cell features.