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    • The patient underwent surgery on

    2019-05-15

    The patient underwent surgery on December 2, 2013. A 13 × 13 cm elastic lobulated yellowish tumor, arising from the upper jejunum with suspected local invasion into the transverse colon and mesentery, was detected intraoperatively. Thus, small bowel segmental resection and left hemicolectomy were performed as radical treatment. Under gross examination by our pathologist, the tumor was observed to arise from the jejunal muscle layer with a focally jagged and infiltrative tumor border and that it extended to the subserosa, serosa, and nearby mesocolon. The muscle layer of the colon and the jejunal mucosa were both uninvolved. The tumor was yellowish, elastic, and firm with areas of necrosis. Microscopically, spindle cells arranged in interwoven fascicles with occasional epithelioid cells were seen radiating from staghorn-like vessels. The spindle cells contained elongated nuclei and eosinophilic fibrillary or granular cytoplasm. The epithelioid cells contained a clear cytoplasm with hyalinized stroma (Fig. 2A, B, C). Mild to moderate nuclear pleomorphism and 6 mitoses/10 high-power field (HPF) were seen (Fig. 2D). The surgical margins were free of tumor involvement. Immunohistochemical studies showed that the tumor cells were diffusely positive for smooth muscle azd2171 (SMA) and h-caldesmon, focally positive for desmin and melan-A, occasionally positive for MiTF, and negative for HMB-45, cytokeratin, CD117, DOG-1, S-100, CD34, CDK4, and MDM-2 (Fig. 2E, F). Taken together, the tumor cells were positive for both myogenic and melanocytic markers. A diagnosis of PEComa with spindle cell predominance was confirmed. Considering the high mitotic rate (6/10 HPF) but limited cellular atypia and pleomorphism, the PEComa was identified as a low-grade malignant tumor. Adjuvant chemotherapy or radiotherapy was not suggested owing to the lack of evidence for clinical benefits.
    Discussion PEComa is a rare subtype of mesenchymal tumor with characteristic expression of both myogenic and melanocytic markers. It harbors a wide range of morphologic appearances with the most common finding of clear to lightly eosinophilic cells arranged in nested, fascicular, or sheet-like patterns. The tumor cells are predominantly epithelioid, predominantly spindle-like, or an admixture of both types and are surrounded by a delicate arborizing capillary network. These unique tumor cells were thus named “perivascular epithelioid cells” (PECs). The PEComa family of tumors includes AML, LAM, and PEComa. AML is commonly seen as an asymptomatic renal lesion with fat, muscle, and blood vessels. Pulmonary LAM presents predominantly in young premenopausal women with progressive multiple nodular and interstitial pulmonary lesions, which may lead to respiratory failure. PEComa is an epithelioid neoplasm typically arising in the gynecological tract, retroperitoneum, GI tract, and soft tissue with variable clinical behaviors. Definitive diagnosis of PEComa is mainly based on pathological examination showing positivity for myogenic markers—including SMA, desmin, and caldesmon—and melanocytic markers—including HMB-45, melan-A, and MiTF—in the characteristic tumor cells (Table 1). Generally, PEComas are diagnosed in middle-aged and predominantly female patients. In one large pooled analysis of 234 cases of PEComa by Bleeker et al., the median age of PEComa patients was 43 years, and 79% of patients were women. The most commonly reported tumor site is the uterus, followed by the skin and the liver. Dolye et al. reported 35 cases of PEComa in the GI tract, which is the largest reported series of GI PEComas. In contrast to previous reports, PEComas in the GI tract do not exhibit gender predilections, and over 90% of tumors are composed of purely or predominantly epithelioid cells. The most common site for GI tract PEComa is the colon followed by the small intestine. Most PEComas follow a relatively benign clinical course, but a subset demonstrates aggressive behavior of local recurrence or distant metastasis. Risk factors associated with recurrence or metastases were proposed by several studies (Table 2). Folpe et al. developed the first and most widely accepted classification utilizing the identified six unfavorable features (tumor size > 5 cm, mitosis >1/50 HPF, necrosis, infiltrative growth pattern, high nuclear grade and cellularity, and vascular invasion). Malignant PEComas are defined as tumors with two or more unfavorable features; benign PEComas, those with no unfavorable features; and PEComas of uncertain malignant potential, those not fulfilling the above conditions. The largest PEComa series reported by Bleeker et al. showed that only primary tumor size ≥5 cm and high mitotic rate (>1/50 HPF) were associated with recurrence. The series of PEComas of the GI tract reported by Doyle et al. demonstrated that marked atypia, diffuse polymorphism, and mitoses ≥2/10 HPF were associated with metastasis. According to the above criteria, our case should be classified as a malignant PEComa and it harbors a risk of recurrence or metastasis.