Laparoscopically resected perivascular epithelioid cell tumor of the ascending colon demonstrating submucosal tumor morphology: a case report

Background: The differential diagnosis for a colonic submucosal tumor (SMT) can include many types of cancer. We report a case of a perivascular epithelioid cell tumor (PEComa), a rare mesenchymal neoplasm that demonstrates SMT morphology, in the ascending colon. Case presentation: A mass was incidentally detected by computed tomography (CT) in a 53-year-old man. Colonoscopy revealed an SMT with central ulceration in the ascending colon, and 18F-uoro-2-deoxy-D-glucose positron emission tomography CT demonstrated a high maximum standardized uptake value of 7.33. Preoperative diagnosis was inconclusive. Given the malignant potential of the tumor, we performed a laparoscopic right hemicolectomy with D3 lymph node dissection. The tumor was 5.5 cm × 4.1 cm and located in the submucosa and muscular propria. There was no lymph node metastasis (0/46). Based on the positive immunohistochemical stainings of both melanocytic (HMB45) and muscle (desmin) markers, we diagnosed the tumor as a PEComa. In the 17 months since surgical resection, the patient has not experienced recurrence, but careful observation should continue because of the malignant potential of the tumor. Conclusions: Although rare, a PEComa should be considered in the differential diagnosis of colonic SMT. Immunohistochemical staining of melanocytic and muscle markers is useful for the diagnosis. . One a large tumor (5.5 cm), mitotic rate (60/50 high-power elds), and 60% tumor necrosis had lymph node and liver metastases at initial diagnosis 21 . Our patient has not experienced recurrence during the 17 months after surgery, although we had concerns because he met ve of Forpe’s six criteria to predict malignancy. Follow-up should be continued because information regarding disease pathology and prognosis is limited. More cases with longer follow-up periods are needed to predict the prognosis of colonic PEComa, although this will be dicult because of the rarity of the tumor. of SMT. Immunohistochemical staining of melanocytic and muscle markers is useful for the diagnosis, although preoperative ndings indicate a malignant potential. More research and case reports are needed to provide guidance for effective PEComa surgery and long-term care.


Background
A colonic submucosal tumor (SMT) constitutes various differential diagnoses including gastrointestinal stromal tumor (GIST), neuroendocrine tumor, smooth muscle tumor, schwannoma, malignant lymphoma, and primary or metastatic colon cancer 1 . We report a case of perivascular epithelioid cell tumor (PEComa) demonstrating SMT morphology in the ascending colon. PEComa is a rare mesenchymal neoplasm with a particular immunohistochemical pro le 3 . We also summarize previous colonic PEComa cases and investigate their clinicopathological characteristics.

Case Presentation
A 53-year-old man with cough and fever but no abdominal symptoms underwent computed tomography (CT), and a mass was incidentally discovered in the right intra-abdominal region. After referral to our hospital, a contrast-enhanced CT showed a 50 mm mass with heterogeneous enhancement (Fig. 1A) and a 10 mm regional lymph node (Fig. 1B). A subsequent colonoscopy showed an SMT with central ulceration in the ascending colon (Fig. 1C). 18F-uoro-2-deoxy-D-glucose (FDG) positron emission tomography CT demonstrated a high maximum standardized uptake value of 7.33 (Fig. 1D). A biopsy taken during the colonoscopy did not provide adequate tumor specimens for pathological investigation. Given the malignant potential of the tumor, we performed a laparoscopic right hemicolectomy with D3 lymph node dissection 2 .
Macroscopic examination revealed a 5.5 cm × 4.1 cm tumor located in the submucosa and muscular propria, protruding into the mucosal and serous surfaces (Figs. 2A and 2B). Central ulceration was con rmed, and the surgical resection margin was negative. There was no lymph node metastasis (0/46). tumor as a PEComa based on the co-expression of melanocytic (HMB45) and muscle (desmin) markers 3 . The histology of the specimen showed a high nuclear grade and cellularity, and the mitotic rate was zero. Both tumor necrosis and lymphovascular invasion were positive, and the Ki-67 index was 13% ( Fig. 3I). There has been no tumor recurrence in the 17 months since the surgical resection.

Discussion And Conclusions
PEComa is a rare mesenchymal neoplasm de ned by the World Health Organization in 2002 as a "mesenchymal tumors composed of histologically and immunohistochemically distinctive perivascular epithelioid cells" 4 . As was seen in our case, a diagnosis can be made by melanocytic markers such as HMB-45 and Melan A and the muscle markers SMA and desmin.
The di culty of obtaining a su cient tumor sample makes the preoperative diagnosis of SMT challenging, particularly in the right-sided colon. Endoscopic ultrasound-guided ne-needle aspiration (EUS-FNA) has recently improved the ability to diagnose SMT; however, EUS-FNA for right-sided colon lesions is still technically complicated and not standardized 5, 6 . In our case, a biopsy taken during colonoscopy did not yield a su cient tumor sample for preoperative diagnosis.
When a biopsy cannot be performed, images can determine the treatment strategy. In our case, the images indicated a potential malignancy according to guidelines presented in the literature 7 : a large tumor size (> 5 cm), heterogeneous enhancement in CT, high FDG accumulation, and central tumor ulceration.
The discovery of a swollen 10 mm regional lymph node further suggested the possibility of malignancy. These ndings provided compelling evidence to perform surgery for both diagnostic and therapeutic purposes, and we did a minimally invasive laparoscopic procedure to perform systematic tumor resection and lymph node dissection.
We did a literature search using PubMed to investigate the clinicopathological features of colonic PEComa and found 21 primary cases, including that of our patient [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] . These are summarized in Table 1. The median age was 36 years (range: 7-62 years), and the percentage of females was 61.9%, suggesting that the patients were predominantly younger and female, as reported in a recent systematic review of GI PEComa 3 . The tumors were found equally on both sides of the colon (right side: 11 cases and left side: 10 cases). The tumors were large (median: 4.8 cm, range: 1.2-10.0 cm), and most patients were symptomatic (85.7%). Preoperative diagnosis of colonic PEComa was di cult in most cases, and only one patient had a suspected PEComa from the specimen obtained under colonoscopy 13 . There was diversity in the extent of surgical resection and lymph node dissection, which could be explained by the di culty of preoperative diagnosis.  25 . One patient with a large tumor (5.5 cm), high mitotic rate (60/50 high-power elds), and 60% tumor necrosis had lymph node and liver metastases at initial diagnosis 21 . Our patient has not experienced recurrence during the 17 months after surgery, although we had concerns because he met ve of Forpe's six criteria to predict malignancy. Follow-up should be continued because information regarding disease pathology and prognosis is limited. More cases with longer follow-up periods are needed to predict the prognosis of colonic PEComa, although this will be di cult because of the rarity of the tumor.
In conclusion, PEComa, although rare, should be considered in the differential diagnosis of colonic SMT. Immunohistochemical staining of melanocytic and muscle markers is useful for the diagnosis, although preoperative diagnosis is di cult. Image ndings could indicate a malignant potential. More research and case reports are needed to provide guidance for effective PEComa surgery and long-term care.

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Written informed consent was obtained from the patient to publish this case report.
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