Tumor Symbiosis: Gastrointestinal Stromal Tumor as a Host for Primary Peritoneal Mesothelioma

Excerpt

A 57-year-old man with a history of polycythemia vera presented for routine primary care follow-up and was found to have anemia with hemoglobin level of 12 mg/dL from 16 mg/dL. He was referred to gastroenterology for upper and lower endoscopies, which revealed an ulcerated submucosal mass in the gastric antrum. Endoscopic ultrasound (EUS) with core needle biopsy revealed a spindle cell neoplasm on hematoxylin and eosin (H&E) staining. Immunohistochemical analyses were positive for CD117 (KIT) and DOG-1, consistent with a gastrointestinal stromal tumor (GIST). Staging computed tomography (CT) of the abdomen/pelvis demonstrated a 15 × 12 × 13 cm gastric mass with effacement of the left liver. He was started on neoadjuvant imatinib (Gleevec, Novartis). Follow-up CT after 3 months of therapy demonstrated a 19% increase in tumor volume and new omental nodules (Fig. 1a). Tumor sequencing revealed a PDGFRA D842V mutation, which is known to be imatinib resistant. Thus, he was switched to dasatinib, but this was poorly tolerated. Therefore, he underwent diagnostic laparoscopy and peritoneal biopsies, which revealed primary peritoneal mesothelioma in addition to the known gastric GIST. He was then referred to our center for possible cytoreduction and hyperthermic intraperitoneal chemotherapy (HIPEC) to treat his mesothelioma. To determine his candidacy for this approach, repeat diagnostic laparoscopy was performed. This revealed the large gastric GIST with invasion, rather than abutment, of hepatic segments 2 and 3. Moreover, there were numerous peritoneal implants coating the surface of the GIST (Fig. 1b). The peritoneal cancer index (PCI) regions of the upper abdomen (e.g., regions 1–3) and along the small bowel (e.g., regions 9–12) were most affected. As compared to the upper abdomen, the pelvis and lower quadrants were essentially spared of mesothelioma. The patient had a PCI score of 17. We proceeded with an exploratory laparotomy, subtotal gastrectomy with an en bloc left lateral sectionectomy and omentectomy for the GIST followed by complete peritoneal cytoreduction (CC0) and HIPEC for the mesothelioma. Final histopathology (Fig. 2a) revealed numerous peritoneal calretinin immunostain-positive tumor deposits that were histopathologically consistent with epithelioid peritoneal mesothelioma (Fig. 2b) with an underlying highly vascularized KIT (C-KIT, CD117) immunostain-positive spindle cell tumor consistent with GIST (Fig. 2c).

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