(P 213) EPITHELIOID INFLAMMATORY MYOFIBROBLASTIC SARCOMA WITH LEUKEMOID REACTION

Objective: Epithelioid inflammatory myofibroblastic sarcoma (EIMS) is a rare and aggressive inflammatory myofibroblastic tumor variant. Our report identifies the first case of EIMS with leukemoid reaction (LR). This is also the first case for which pancreatic infiltration occurred from the disease onset.

Methods: A previously healthy 14-year-old male patient presented with an 18×18×10 cm mass at the retroperitoneal space and a white blood cell count (WBC) of 85×10^9/L. The mass, pancreatic body and tail, spleen, partial transverse and descending colon and corresponding mesentery, and omentum were surgically removed with no visible remnants. The WBC count returned to 16×10^9/L after surgery, but rose to 41×10^9/L four days later. Then we took the bone marrow (BM) aspiration and biopsy, which showed normal cellularity with myeloid hyperplasia and intact maturation and morphology. BM immunophenotyping showed a mature granulocyte pattern, cytogenetics showed 46, XY, and molecular analysis revealed negative myeloproliferative neoplasm mutations and fusion genes. Histological examination of the retroperitoneal mass showed most of the tumor cells were epithelioid-to-round with vesicular chromatin, large nucleoli, and mitosis around 10–30/10 HPF. About 20% of the tumor cells were spindle (Figure 3). The tumor extensively invaded the pancreas, adipose tissue of the splenic hilum, and mesentery of the colon. The margins were free of tumor. Immunohistochemistry indicated ALK-positive cytoplasm staining with perinuclear accentuation (Figure 4), vimentin+, desmin-, SMA-, CK-, CD30 (scattered+), myogenin-, TP53+, Ki-67 (70%+), calponin-, and S-100-. FISH showed ALK rearrangement. These findings were consistent with the diagnosis of EIMS and LR.

Results: The patient's condition was stable during the first week after surgery; however, about ten days after surgery, pancreatic fistula, abdominal bleeding, fever, and colonic anastomotic fistula appeared successively. Chemotherapy and targeted drugs were not given due to his unstable condition. After treatment, the aforementioned fever and other symptoms were gradually controlled. Unfortunately, symptoms of gastrointestinal obstruction appeared and gradually worsened one month after surgery. CT and angiography revealed the retroperitoneal tumor recurred with hepatic and pulmonary metastasis. The patient died three months after disease presentation with a 183×10^9/L WBC.

Conclusion: EIMS is a highly aggressive inflammatory myofibroblastic tumor variant. Since ALK rearrangement presents in all EIMS, the combination therapy of surgical resection and crizotinib or other targeted drugs may be a potential treatment. Disease understanding and study of EIMS among pathologists and clinicians need to be strengthened to improve prognosis of this disease.