A case of successful detection of disseminated gastrointestinal stromal tumors by ascites smear cytology using cell block preparation with DOG1 immunostaining.

Cytological features of gastrointestinal stromal tumors (GISTs) have been reported, especially regarding fine-needle aspiration cytology, including immunostaining for c-kit and DOG1. Meanwhile, cytological findings of GISTs on ascites cytology have rarely been reported, which may be owing to the rare appearance of GIST tumor cells in ascites. Herein, we present a 66-year-old woman who had disseminated GISTs in the abdomen. The GIST tumor cells appeared sparsely in the ascites smear cytology using ascites obtained at the time of autopsy. Even when widespread intra-abdominal dissemination takes place, GISTs may be hard to detect in ascites smear cytology, based on the experience of this case. However, immunohistochemistry of DOG1 using a cell block preparation was found to clearly visualize the GIST tumor cells, although they were sparsely present. Immunostaining of c-kit did not provide as clear an identification of the tumor cells as DOG1 did. When suspicious about GISTs, it is wise to prepare a cell block to make it possible to visualize the tumor cells immunohistochemically.