Gastrointestinal Stromal Tumor: Chondro-Myxoid Variant Mimicking Chondrosarcoma

SW, an 84-year-old African American female, presented to an outside institution complaining of dull, intermittent abdominal pain in the anterolateral and suprapubic regions. Decreased appetite, nausea, and general weakness accompanied this pain. Physical exam revealed a soft, non-tender mass in the left upper quadrant that extended 20 cm below the costal margin. A separate 2 cm mass, in the periumbilical area, was also palpable. A CT scan (Figure 1) was performed and revealed a large, soft tissue mass in the left upper quadrant extending from the gastroesophageal junction to the mid-abdomen. The mass seemed to originate from the stomach compressing the stomach medially, and the pancreas and spleen inferiorly and laterally. The periumbilical mass was subcutaneous and separate from the larger mass. A fine needle aspiration and biopsy of the umbilical mass was diagnosed as a myxoid chondrosarcoma. No further therapy was given at that time. Approximately four months later, the patient presented to our institution with nausea, abdominal pain, and increased regurgitation of food. Given the clinical presentation, radiologic findings, and biopsy results, the patient was felt to have a primary sarcoma of the stomach. Since the patient was an appropriate surgical candidate, she was taken to the operating room. Upon laparotomy, a large mass, originating from a pedicle attached to the greater curvature of the stomach, was observed. The tumor was adherent to the diaphragm and to the lateral segment of the liver. No invasion of any other adjacent structures was observed. The periumbilical mass appeared to be a portion of the original tumor that had become incarcerated in an umbilical hernia defect that had fractured away from the dominant lesion. On gross pathologic examination, a 7012 gram, multinodular, cerebreform mass, was observed to be arising from within the wall of the greater curvature of the stomach. This mass extended from near the gastroesophageal junction to the pyloris. The tumor showed expansive intra-abdominal growth and involved the omentum and anterior abdominal wall. Sectioning showed a heterogeneous, lobulated, gray-white mass with areas of necrosis, hemorrhage, and cystic degeneration (Figure 2). The tumor had a variable histologic appearance. Portions of the tumor were relatively hypocellular with a vaguely nodular, but prominent chondroid matrix. Dispersed within this matrix were discohesive epithelioid cells. Focal areas of myxoid cystic degeneration were also present. The majority of the tumor was extremely cellular containing sheets of epithelioid cells within a chondroid matrix. Additionally, other areas had more spindle-shaped cells. These cells showed nuclear palisading and were aligned in a perivascular distribution. Focally, these cells formed microcysts. Tumor cell necrosis, hemorrhage, and high mitotic activity (65/50 hpf) was observed in these spindle cell areas. The differential diagnosis of this tumor upon H&E staining included a chondrosarcoma and a gastrointestinal stromal tumor (Figure 3). S100 staining, which should be positive in >95% of chondrosarcomas, was negative. The tumor cells were positive for c-kit (CD-117), CD-34, CD-99 (mic2), and smooth muscle actin (SMA) (Figure 3). This staining pattern confirmed