perivascular epithelioid cell tumor ( pecoma ) is a family of related mesenchymal neoplasms that include angiomyolipoma , lymphangiomyomatosis and clear cell ' sugar ' tumor of the lung , and a group of rare , morphologically and immunophenotypically similar lesions arising at a variety of visceral and soft tissue sites1 ) . it has distinct histological and immunohistochemical features defined by coexpression of melanocytic ( hmb-45 ) and smooth muscle markers ( smooth muscle actin and desmin ) , but negativity to s-100 protein2 ) . data on gastrointestinal ( gi ) pecoma remain limited to isolated case reports . to our knowledge , 17 cases have been reported in the literature , among which 10 occurred in adults3 ) . because of the rarity of pecoma , its clinical , phenotypic and biological characteristics are not fully understood , and little is known about prognosis and treatment modalities for pecoma . however , chemotherapy and radiotherapy have been used in locally advanced , metastatic and histologically malignant cases . we report a child with pecoma in the ascending colon , treated by surgical excision and interferon-2b ( ifn-2b ) immunotherapy . a previously healthy 7-year - old boy was admitted to our hospital because of hematochezia and abdominal pain . there was no history of bleeding disorders , recent infection , change in bowel habits , or significant weight loss . a complete blood count showed white blood cell 11,500/mm , hemoglobin 8.2 g / dl , hematocrit 26.0% , mean corpuscular volume 72.4 fl , platelet 401,000/mm and other biochemical tests were normal . 1a ) and colonoscopy displayed a 3.9 cm - sized pedunculated mass at the hepatic flexure of the ascending colon . examination of the resected colon revealed a 43 cm in size , polypoid , yellow and partially brown mass ( fig . the tumor cells were predominantly epithelioid cells having prominent nuclei and abundant cytoplasm ( fig . the tumor was low - grade malignancy as evidenced by infiltrative growth but mild cellular atypia , low mitotic and proliferation index without necrosis and no vascular invasion . all of the surgical margins were free of tumor . a metastatic workup including a bone scan , positron emission tomography , brain and chest ct was negative . he was treated with adjuvant ifn-2b therapy ( intron - a , schering - plough , kenilworth , new jersey , new jersey , usa ) : 3 million iu / m , 3 times / week , subcutaneous injection , for 1 year . short term side effects , such as fever , neutropenia and skin necrosis , were not seen in the present case . a recently defined pecoma is a rare mesenchymal neoplasm of uncertain malignant potential affecting various organs . at first , bonetti et al4 ) proposed the concept of perivascular epithelioid cell ( pec ) in 1992 and the terminology ' pecoma ' was suggested by zamboni et al5 ) in 1996 . the world health organization accepted the designation ' pecomas , ' defining them as mesenchymal neoplasms that share the same distinctive cell type , the pec in 2002 . pecomas have been reported in several organs including the uterus , falciform ligament , prostate , small and large bowel , rectum , lung , breast , cardiac septum , liver , kidney , pancreas and soft tissue of the thigh . a review of 51 cases of pecoma documented in the literature revealed that 90% of cases affected females and 41% involved the uterus6 ) . in the pediatric population , there have been only a few documented pecomas in several organs including the duodenum , appendix , transverse colon , sigmoid colon , rectum , kidney , broad ligament , vagina and orbit . to our knowledge , 17 cases of gi pecomas have been reported in the literature , among which 10 occurred in adults3 ) . pediatric gi pecomas were documented in rectum3 , 7 , 8) , appendix9 ) , duodenum10 ) , sigmoid colon11 ) and transverse colon12 ) . this report is the eighth documented case of the pediatric gi pecoma , and the third documented case of the pediatric colon pecoma . the tumor cells have large epithelioid appearance with abundant clear to granular eosinophilic cytoplasm and a large vesicular nucleus . immunohistochemically , pecoma expresses myogenic and melanocytic markers , such as hmb45 , hmsa-1 , melana / mart1 , microophthalmia transcription factor ( mitf ) , actin and , less commonly , desmin13 ) . on ultrastructural analysis , pecoma contains microfilament bundles with electron - dense condensation , numerous mitochondria and membrane - bound dense granules . little information is available on the possible molecular alterations occurring in pecomas . in one report , the loss of chromosome x and a t(3;10 ) translocation were identified by conventional cytogenetic techniques14 ) . in another report , histologic criteria indicative of malignant potential in pecomas have not been established , especially in the pediatric age group . however , in a recent study of pecoma of soft tissue and gynecologic origin , folpe et al15 ) suggested criteria to separate pecomas into benign , uncertain malignant potential , and malignant categories . they proposed that malignancy was predicted by the presence of 2 or more of the followings : tumor size greater than 5 cm , infiltrative tumor border , high nuclear grade and cellularity ; more than 1 mitosis/50 high - power fields , tumor necrosis , and vascular invasion . in the present case his tumor was regarded as low grade , as evidenced by infiltrative tumor border but lacking of other findings listed above . however , locally advanced or metastatic disease portends a poor prognosis and strategies incorporating chemotherapy , radiation and immunotherapy have been reported . various responses , including complete , partial or absent responses , have been noted for dacarbazine , vincristine and imatinib mesylate . rigby et al16 ) reported an 11-year - old girl with metastatic renal pecoma treated with dacarbazine based chemotherapy and imatinib mesylate . she presented with two large abdominal masses in the left flank and epigastrium and left supraclavicular lymphadenopathy . the tumor did not respond to an initial treatment of chemotherapy , including dacarbazine , bicnu and vincristine . a trial of imatinib mesylate based on the expression of c - kit was unsuccessful because of the lack of response and adverse effects of the drug . among 7 pediatric gi pecoma cases reported so far , six were treated with surgery alone7 - 12 ) , and the last was treated with surgery and adjuvant chemotherapy consisting of doxorubicin , ifosfamide , and mesna on the basis of non - rhabdomyosarcoma soft tissue sarcoma protocol arst0332 by children 's oncology group3 ) . adjuvant ifn-2b was used in patients with melanoma17 ) , and for immunotherapy in a patient with pecoma of the bladder18 ) . it reduced neomicrovascular density in the normal urothelium adjacent to the tumor after transurethral resection of superficial bladder carcinoma19 ) . outpatient treatment with subcutaneous ifn-2b plus interleukin-2 treatment for metastatic renal cell cancer was also reported . eight of 47 patients ( 17% ) responded to this regimen and overall response rate was similar to that seen with high - dose interleukin-2 alone , however , the response duration appeared to be shorter20 ) . while ifn-2b therapy for the management of pecoma remains experimental , we decide to use ifn-2b based on the vascular nature of this tumor and its anti - angiogenic effect . the present case represents the first documented pediatric gi pecoma treated with surgical resection and adjuvant ifn-2b immunotherapy . further studies involving larger number of cases and close monitoring by long - term follow - up are required in the light of its potential for local recurrence and distant metastasis .