Surgical experience of adult primary hepatic sarcomas.

BACKGROUND: Primary hepatic sarcoma (PHS) is a rare primary liver malignancy. The histological types of PHS are diverse, and the clinical outcomes and management mainly depend on the histopathology. This study aims to evaluate the results of surgical intervention. METHODS: Between January 2003 and June 2009, 13 adult patients with pathologically proven PHS were identified by record review. The patients' demographic profile, tumor characteristics, treatment modalities, and outcomes were reviewed and analyzed. The end of follow-up was December 2014. RESULTS: Nine (69%) underwent curative liver resection and two underwent liver transplantation; the others received non-operative treatments. The pathologic findings were six (46%) angiosarcomas, four (30.7%) undifferentiated sarcomas, one (7.6%) leiomyosarcoma, one (7.6%) malignant mesenchymoma, and one (7.6%) hepatic epithelioid hemangioendothelioma. The median follow-up was 31.4 (2.8 ~ 142.5) months. The 1-, 2-, and 5-year survival of surgical patients were 72.7%, 63.6%, and 36.4%, respectively. Importantly, the 1-, 2-, and 5-year survival rates of non-angiosarcoma patients were superior to those of angiosarcoma (85.7% vs. 33.3%, 71.4% vs. 16.7%, and 57.1% vs. 0%, respectively, P = 0.023). CONCLUSIONS: Surgical intervention provides the possibility of long-term survival from PHS. Angiosarcoma is associated with a more dismal outcome than non-angiosarcoma.

[Diagnosis and treatment of prostatic malignant mesenchymal tumors: Analysis of 20 cases].

OBJECTIVE: To explore the diagnosis, treatment, and prognosis of prostatic malignant mesenchymal tumors (PMMT). METHODS: We retrospectively analyzed the clinical and follow-up data about 20 cases of PMMT and reviewed the literature relevant to the diagnosis, treatment, and prognosis of the disease. RESULTS: Based on the results of pathology and immunohistochemistry, the 20 PMMT cases included leiomyosarcoma (n = 7), rhabdomyosarcoma (n = 5), prostatic stromal sarcoma (n = 3), chondrosarcoma (n = 1), and undifferentiated PMMT (n = 4). Twelve of the patients were treated by radical prostatectomy (3 concurrently by sigmoid colostomy and 1 by cystostomy), 2 by pelvic tumor resection following arterial embolization, 1 by total pelvic exenteration, 1 by colostomy with pelvic lymph node biopsy, and 4 by conservative therapy because of metastasis to the lung, pelvis and bone. Of the 20 patients, 9 died of systemic metastasis within 3 months after treatment, 3 died at 6, 7, and 14 months, respectively, 3 survived with tumor for 5, 11, and 12 months, respectively, 2 survived without tumor for 12 and 24 months so far, all subjected to periodic chemotherapy postoperatively, and 3 lost to follow-up. CONCLUSION: PMMT is a tumor of high malignancy and rapid progression, for which transrectal ultrasound-guided biopsy remains the main diagnostic method. The clinical stage of the tumor is an important factor influencing its prognosis and the survival rate of the patients can be improved by early diagnosis and combined therapy dominated by radical prostatectomy.

Conservative approach in localised rhabdomyosarcoma of the bladder and prostate: results from International Society of Paediatric Oncology (SIOP) studies: malignant mesenchymal tumour (MMT) 84, 89 and 95.

BACKGROUND: The three sequential SIOP MMT studies provide the largest dataset available to date, to define the patient and tumour characteristics, treatment modalities and event-free and overall survival for children with non metastatic rhabdomyosarcoma (RMS) of the bladder and/or prostate (BP). PROCEDURE: The combined dataset of 172 patients with BP RMS treated on the SIOP MMT 84, 89 and 95 studies was reviewed to determine tumour characteristics, details of treatment and outcome. RESULTS: Median age at diagnosis was 2.5 years (range 2 months-17.8 years) and 138 (79%) were males. Median follow-up was 11.4 years (range 3 months-22 years). The 5-year overall survival of the combined cohort was 77% (CI 70-83%). The 5-year event-free survival was 63% and included 7 patients (4%) who did not achieve complete remission (CR), and 57 (33%) who relapsed. Age ≥ 10 years (RR 3.7) and alveolar pathology (RR 3.3) were identified as independent prognostic factors on multivariate analysis. Fifty-nine (50%) of the 119 survivors were cured without significant local therapy, improving from 31% in MMT84 study to 61% in MMT95 study. CONCLUSION: The clinical strategy of the MMT studies aims to minimise the burden of therapy whilst maintaining survival rates. Overall survival is comparable to that of other international groups, despite the lower use of radiotherapy and or radical surgery, although number of events experienced is higher. Further assessment of the late effects of therapy is required to confirm whether this approach results in lower morbidity in the long-term.

Malignant ectomesenchymoma in children and adolescents: report from the Cooperative Weichteilsarkom Studiengruppe (CWS).

BACKGROUND: Malignant ectomesenchymoma (MEM) is a soft tissue tumor with heterologous rhabdomyoblastic components believed to arise from pluripotent migratory neural crest cells. To date merely 50 cases have been published and the knowledge about the course of disease and optimal treatment is limited. METHODS: Six patients with MEM were registered 1996-2009. The diagnosis was confirmed according to current criteria. Their treatment and outcome was analyzed. RESULTS: The median age of the three females and three males was 0.6 years (range, 0.2-13.5). The mesenchymal component in all tumors was rhabdomyosarcoma (RMS), the neural component ganglioneuroblastoma/neuroblastoma (n = 5) and peripheral primitive neuroectodermal tumor in one case. Five patients presented with localized, one with metastatic disease. All but one patient received multiagent chemotherapy during their initial treatment. The tumors of 4/5 patients with localized MEM were at least grossly resected at best surgery; the patient without gross resection was additionally irradiated. Three of four evaluable tumors responded well to induction chemotherapy. All patients achieved a first complete remission (CR), but three recurrences (two local, one systemic) occurred. The individual with metastatic MEM did not survive, but all five patients with localized MEM are currently alive in CR with a median follow-up of 5 years (range: 2.1-13.7). CONCLUSIONS: Risk-factors and outcome of MEM appear to be comparable with other highly malignant pediatric soft tissue sarcoma when a multimodal treatment strategy including chemotherapy and adequate local treatment is pursued. We propose that treatment of patients with MEM be done according to pediatric protocols similar to other rhabdomyosarcoma-like soft tissue sarcoma.

Paratesticular alveolar rhabdomyosarcomas do not harbor typical translocations: a distinct entity with favorable prognosis?

The alveolar subtype of rhabdomyosarcoma (RMA) is a strong risk factor. Cases of RMA located in paratesticular sites have however been reported to have similar outcomes to those of embryonal rhabdomyosarcoma (RME). We wanted to re-evaluate the impact of subtype in paratesticular rhabdomyosarcoma (PT-RMS). Patients from a population-based cohort diagnosed with paratesticular RMA in 1990-2013 were analyzed. All tumor samples were re-reviewed using conventional morphology, immunohistochemistry, and molecular testing. Seven patients were eligible. Four tumors showed focal areas morphologically compatible with RMA (mixed RMA/RME). One case was undifferentiated, with a solid round-cell morphology which had to be reclassified as poorly differentiated RME. Two cases had a "microalveolar" morphology which is today regarded as sclerosing RME. No tumor showed the characteristic gene fusion of RMA. Five children had localized disease, one bone metastases, and another lymph-node involvement. All primaries were grossly resected. One locoregional relapse occurred. At a median follow-up of 7 years, all patients were alive disease-free. PT-RMS can show a focal alveolar histology combined with typical features of RME. In current morphological classifications, all rhabdomyosarcomas qualify for the alveolar subtype if typical features of RMA are realized at least focally. Rhabdomyosarcomas consisting of pure RMA morphology were however not found in our patients with PT-RMS. The mixed RMA/RMEs identified in our population-based study did not show a translocation typical for RMA and had a good prognosis. Further prospective studies need to evaluate if mixed RMA/RMEs have a similar favorable outcome in non-paratesticular sites as well.

Nonparameningeal head and neck rhabdomyosarcoma in children and adolescents: Lessons from the consecutive International Society of Pediatric Oncology Malignant Mesenchymal Tumor studies.

BACKGROUND: This article reports risk factors and long-term outcome in localized nonparameningeal head and neck rhabdomyosarcomas in children and adolescents from a combined dataset from 3 consecutive international trials. METHODS: Data from 140 children (9.3% of total) prospectively enrolled in the International Society of Pediatric Oncology Malignant Mesenchymal Tumor (SIOP-MMT)-84/89/95 studies were analyzed. RESULTS: Primary site was: superficial face in 46%; oral cavity (21%); neck (19%); and salivary glands (14%). Local control was achieved in 96%, but 49% relapsed (locoregionally 91%). At median follow-up of 10 years, 5-year overall survival (OS) was 74.7% (67.4% to 81.9%) and event-free survival 48.9% (40.6% to 57.2%), although this improved with successive studies. Radiotherapy (RT) as first-line treatment was independently prognostic for event-free survival (relative risk [RR] = 0.4 [range, 0.2-0.7]; p < .01) even if it did not impact OS (RR = 1 [range, 0.5-2]). CONCLUSION: High rates of locoregional relapse were seen in head and neck rhabdomyosarcoma that should be prevented by more frequent use of RT in this primary. © 2016 Wiley Periodicals, Inc. Head Neck 39: 24-31, 2017.

Trends in incidence and survival of mesenchymal neoplasm of the digestive tract within a defined population of northern Norway.

Population-based incidence and survival data for gastrointestinal stromal tumor (GIST) are sparse due to the fact that GIST is a rather novel entity both clinically and pathologically, and has not been registered as a separate entity in population-based cancer registries. The aim of the present study was to reclassify all mesenchymal tumors within a defined population of northern Norway over a time-span of 30 years with the purpose of estimating trends of incidence and survival. One hundred and forty-one patients with mesenchymal neoplasms of the digestive tract were identified: 102 as GISTs, 32 as leiomyomatous tumors, 4 as schwannomas, and 3 as fibromas. Incidence rates of GIST showed a significant increase over the whole period, which was not observed for the non-GIST cases. Analysis of GIST cases showed that cases with more than 5 mitoses per 50 high power fields had an increased expected mortality 4 times that of those with fewer mitoses, and the combination of mitotic count and size of tumor can be recommended for categorizing the tumors into different risk levels. The study confirms that GIST is by far the most frequent mesenchymal neoplasm of the digestive tract and that the incidence has increased over the last 30 years.

[Malignant solid tumors in neonates: a study of 71 cases]. / Tumeurs solides malignes néonatales: à propos de 71 cas.

UNLABELLED: Malignant neonatal tumors are rare and comprise 2% of childhood malignancies. Clinical features, histologic types, prognosis were very different from those seen in older children, facing oncologists with diagnostic, therapeutic and ethical problems. PATIENTS AND METHODS: In a retrospective study from January 1987 to January 2004, we reviewed the management of neonates treated at the Institute Gustave Roussy for a malignant solid tumor for whom symptoms started in the first month of life. RESULTS: Seventy-one neonates were treated, comprising 1,2% of the overall patients treated during the same period of time. Of these 71 patients, 42 (59%) presented with neuroblastomas, 12 (17%) with mesenchymal tumors, 6(8%) with cerebral tumors and 11 with various other types of tumors. Fifty-nine patients underwent surgical resection. Thirty-eight neonates received chemotherapy, administered at a 30 to 50% reduced dose. Hematologic toxicities and infections were the main therapeutic complications. Very small doses of radiotherapy were used in only 5 children. There has been no therapy-related mortality. Twenty-two of the 57 survivors have sequelae, especially patients with intraspinal neuroblastoma. The 5 year overall survival was 79%. CONCLUSIONS: Neonatal malignant solid tumors, except for cerebral tumors, have a good prognosis. The young age of patients resulted in problems of treatment tolerance. The therapeutic regimen should take into account the risk of acute iatrogenic toxicity and long term sequelae. Surgery remains the treatment of choice but chemotherapy, with dose reduction, managed by expert teams, is essential and safer in a lot of case.

Integrative Modeling Reveals Annexin A2-mediated Epigenetic Control of Mesenchymal Glioblastoma.

Glioblastomas are characterized by transcriptionally distinct subtypes, but despite possible clinical relevance, their regulation remains poorly understood. The commonly used molecular classification systems for GBM all identify a subtype with high expression of mesenchymal marker transcripts, strongly associated with invasive growth. We used a comprehensive data-driven network modeling technique (augmented sparse inverse covariance selection, aSICS) to define separate genomic, epigenetic, and transcriptional regulators of glioblastoma subtypes. Our model identified Annexin A2 (ANXA2) as a novel methylation-controlled positive regulator of the mesenchymal subtype. Subsequent evaluation in two independent cohorts established ANXA2 expression as a prognostic factor that is dependent on ANXA2 promoter methylation. ANXA2 knockdown in primary glioblastoma stem cell-like cultures suppressed known mesenchymal master regulators, and abrogated cell proliferation and invasion. Our results place ANXA2 at the apex of a regulatory cascade that determines glioblastoma mesenchymal transformation and validate aSICS as a general methodology to uncover regulators of cancer subtypes.

Cisplatin therapy for disseminated mixed mesodermal sarcoma of the uterus.

Eighteen patients with metastatic mixed mesodermal sarcoma of the uterus received cisplatin therapy at the University of Texas (UT) M.D. Anderson Hospital and Tumor Institute at Houston. The dose of cisplatin varied from 75 mg/m2 to 100 mg/m2. Previous therapy included surgery in 11 patients, radiotherapy in two patients, and surgery plus radiotherapy in four patients. One patient had no prior therapy. Seven patients had also received prior chemotherapy with doxorubicin. Of 12 patients with measurable disease, one (8%) had a complete response and four (33%) had a partial response for an overall response rate of 42%. The median progression-free survival of patients treated with cisplatin as first- and second-line therapy was 4.5 and 5.5 months, respectively. Cisplatin demonstrated moderate activity with mild toxicity in this group of patients with metastatic mixed mesodermal uterine sarcomas. Further studies including cisplatin-containing combination regimens seem to be warranted.

Tumor angiogenesis and its clinical significance in pediatric malignant liver tumor.

AIM: To investigate the expression of vascular endothelial growth factor (VEGF) and microvascular density (MVD) count in pediatric malignant liver tumor and their clinical significances. METHODS: Fourteen children with malignant liver tumors including seven hepatocellular carcinomas (HCCs), five hepatoblastomas, one malignant mesenchymoma and one rhabdomyosarcoma were studied. Twelve adult HCC samples served as control group. All samples were examined with streptavidin-biotin peroxidase (SP) immunohistochemical staining for VEGF expression and MVD count. RESULTS: VEGF positive expression in all pediatric malignant liver tumors was significantly higher than that in adult HCC (0.4971+/-0.14 vs 0.4027+/-0.03, P<0.05). VEGF expression in pediatric HCC group was also markedly higher than that in adult HCC group (0.5665+/-0.10 vs 0.4027+/-0.03, P<0.01) and pediatric non-HCC group (0.5665+/-0.10 vs 0.4276+/-0.15, P<0.05). The mean value of MVD in pediatric malignant liver tumors was significantly higher than that in adult HCC (33.66+/-12.24 vs 26.52+/-4.38, P<0.05). Furthermore, MVD in pediatric HCC group was significantly higher compared to that in adult HCC group (36.94+/-9.28 vs 26.52+/-4.38, P<0.05), but there was no significant difference compared to the pediatric non-HCC group (36.94+/-9.28 vs 30.37+/-14.61, P>0.05). All 7 children in HCC group died within 2 years, whereas the prognosis in pediatric non-HCC group was better, in which two patients survived more than 5 years. CONCLUSION: Children with malignant liver tumors, especially with HCC, may have extensive angiogenesis that induces a rapid tumor growth and leads to a poor prognosis.

Spindle cell variants of embryonal rhabdomyosarcoma in the paratesticular region. A report of the Intergroup Rhabdomyosarcoma Study.

We reviewed 173 cases of paratesticular rhabdomyosarcoma (RMS) of Intergroup Rhabdomyosarcoma Studies (IRS)-I, -II, and -III for evaluation of possible histological factors that might account for the good prognosis of these patients. Almost all cases (161 of 173 cases, 93.1%) occurring in this site were of embryonal histology. A spindle-cell subtype of embryonal RMS was identified that presented a storiform growth pattern with abundant collagen between the tumor cells in most cases. Other tumors of this subtype showed an arrangement of tumor cells in bundles with a low to moderate amount of collagen, resembling a leiomyosarcoma. The other embryonal RMS in this site had the classical embryonal cytology. The spindle-cell subtype was highly differentiated by immunohistochemistry and electron microscopy. Lymph node metastasis was found in seven of 43 patients (16.3%) with a RMS of spindle-cell subtype, compared with 40 of 112 patients (35.7%) with RMS of non-spindle-cell type. Clinical data from patients with spindle-cell subtypes of the paratesticular lesions revealed that they almost always had an association with clinical groups of limited disease (32 patients, 74.4%, with Group I; 10 patients, 23.3%, with Group II disease) and a significantly better prognosis (95.5% survival at 5 years) when compared with patients with the classic embryonal variant of RMS (80% survival at 5 years, p < 0.035). The incidence and anatomic distribution of this spindle cell subtype of embryonal RMS was estimated on 800 randomly selected patients from IRS-II. It was found in the head and neck, extremities, orbit, and some other sites, but 30.6% were located in the paratesticular area. Patients with spindle cell RMS of nonparatesticular sites usually had more extensive disease compared with patients having paratesticular lesions; two thirds of the cases had gross residual tumor after surgery or metastatic tumor at diagnosis. We conclude that spindle-cell RMS is a subtype of embryonal RMS with a very favorable prognosis. The site factor of the paratesticular localization may allow earlier diagnosis of the spindle-cell lesions compared with other sites. Other unknown factors may also play a role.

Mixed mesodermal sarcoma of the ovary.

Three cases of mixed mesodermal sarcoma (MMS) are reported and a review of 90 cases from the English literature is presented. All cases were analyzed with regard to clinical features, prognosis, and therapeutic efficacy. The histogenesis of these rare tumors is discussed and a new classification of ovarian sarcomas is proposed. MMS usually afflicts the postmenopausal women and occurs more often in the nulliparous female. The disease is usually advanced (Stage III) when diagnosed and thus provides a difficult challenge to any postoperative therapy.

Thirty years of experience with pediatric primary malignant liver tumors.

Since 1950, 48 infants and children from 10 weeks to 16 years of age presented with primary hepatic malignancy. Signs and symptoms ranged from asymptomatic to those of malignant disease. All patients had a palpable abdominal mass. Jaundice was seen in five patients, four of whom had preexisting cirrhosis. Three male children had evidence of precocious puberty. Whereas liver function tests were usually normal, alpha-fetoprotein levels, when elevated, proved useful diagnostically and as a tumor marker in follow-up. Hepatic angiography and computed tomography (CT) scans have provided the most valuable preoperative assessment of hepatic architecture. Sixteen infants and children underwent resection for cure. Eleven of these patients are alive and disease free 6 months to 23 years later. Six additional patients had incomplete resection with subsequent radiotherapy and/or chemotherapy; only one such patient is disease-free past 3 years. Twenty-six tumors could only be biopsied; most of these patients died within 12 months regardless of what treatment they received. The histology was hepatoblastoma in 39 patients, hepatocellular carcinoma in 4, fibrolamellar carcinoma in 4, and malignant mesenchymal tumor (mesenchymoma) in 1. The patients with hepatocellular carcinoma and mesenchymoma all died. Three of four patients with fibrolamellar carcinoma are alive and disease-free following resection up to 3 years; this histology seems favorable. The other survivors had hepatoblastoma. The role of adjunctive chemotherapy and/or radiotherapy has not yet been determined.

[Immunohistochemical and ultrastructural heterogeneity of gastrointestinal stromal tumors]. / Hétérogénéité immunohistochimique et ultrastructurale des tumeurs stromales digestives.

AIMS AND METHODS: Digestive stromal tumors are the most frequent undifferentiated mesenchymal tumors. The prognosis of these tumors is difficult to predict and the histogenesis is still subject to controversy. However, the frequent and specific expression of CD117 (c-kit) by these tumors could suggest an origin from interstitial cells of Cajal. The aim of this study was to analyse the histological and immunohistochemical characteristics of 46 digestive stromal tumors surgically resected, with comparaison of CD34 and CD117 expression in these tumors. Sixteen tumors were analyzed on electron microscopy. RESULTS: Sixty three and 74% of the stromal tumors were positive for CD117 and CD34 respectively. While CD117 expression was similar in all locations, on the contrary, there was a decreasing gradient of CD34 expression between gastric (87%) and jejunal (33%) tumors. All tumors with skeinoid fibers expressed CD117. Focal expression of smooth muscle actin was noted in 43% of the cases. The ultrastructural study showed no correlation with the immunohistochemical results. CONCLUSION: Digestive stromal tumors show an immunophenotypic and ultrastructural heterogeneity. CD117 expression is frequent, but not constant.

[A clinical analysis of 153 uterine sarcomas].

OBJECTIVE: To evaluate the prognostic factors and treatment methods of 153 uterine sarcomas. METHODS: 153 cases of the uterine sarcoma were eligible for this retrospective study. Of the 153 cases, 48 were leiomyosarcomas, 47 mixed mesodermal sarcomas, 37 endometrial stromal sarcomas, 8 carcinosarcomas, 4 sarcoma botryoides, 1 fibrosarcoma, and 8 malignant lymphomas. 81 cases were in stage I, 11 stage II, 33 stage III and 11 stage IV. 38 cases were treated by surgery alone, 24 by surgery combined with radiation therapy, 50 by surgery plus chemotherapy, 23 by surgery plus radiation therapy and chemotherapy, 4 by radiation therapy alone, 3 by chemotherapy alone, and 11 by radiation therapy plus chemotherapy. RESULTS: The overall 5-year survival rate was 49.0%, and that of leiomyosarcomas, mixed mesodermal sarcomas and endometrial stromal sarcomas was 46.9%, 34.1% and 69.3% respectively (P < 0.01). The 5-year survival rate of lesions limited to the uterus (stage I + II), and that of pelvic cavity invasion (stage III) and distant metastases was 59.6%, 25.6% and 10.0% respectively (P < 0.01. When the uterus was smaller than a 3 months pregnant uterus, the 5-year survival rate was 49.9%. When the uterus size larger than a 3 months pregnant uterus, the survival rate was 18.8% (P < 0.05). Premenopausals surviving 5-year accounted for 56.3% and post-menopausal 28.9% (P < 0.01). CONCLUSIONS: The prognosis of uterine sarcoma is significantly associated with histologic type, clinical and surgico-pathological stage, uterine size and pre- or post-menopausal status. Radiation or chemotherapy alone is palliative. Postsurgical adjuvant radiotherapy significantly decreased vaginal and pelvic recurrences rates. A combination of surgery, radiotherapy and chemotherapy can reduce pelvic recurrence as well as enhance survivals.

[9 years' survival of a patient with malignant mesenchymoma]. / 9-Letnie przezycie kobiety z mesenchymoma malignum.

The authors present diagnostic and therapeutic documentation of a very rare case of a tumour with mesenchymoma malignum texture in a 48-year old woman operated because of uterine myomas. After the surgery (total hysterectomy and adnexectomy by Freund procedure) followed by radiotherapy and chemotherapy, the patient survived nine years. At the bottom of the therapeutic success lies incidental very early discovery of the tumour and combined treatment of this kind of sarcoma, extremely malignant, thanks to operative therapy of uterine myomas.

Gastrointestinal stromal tumors presenting as omental masses--a clinicopathologic analysis of 95 cases.

Gastrointestinal stromal tumors (GISTs), generally KIT-positive and KIT/PDGFRA mutation-driven mesenchymal neoplasms, most commonly originate from the stomach or small intestine, but in rare examples they involve the omentum. In this study, we analyzed 95 GISTs surgically designated as the omental masses. These tumors occurred in 49 males and 46 females with a median age of 60 years (range: 27 to 88 y). They formed single (n=51) or multiple masses (n=39); 5 cases were equivocal in this respect. Of the single tumors, 21 had no evidence of gastrointestinal tract involvement, 25 were attached to stomach, and 3 were attached to small intestine. Clinicopathologic parameters and prognosis of the 2 former groups were similar. Single tumor cases showed a median mitotic count of 2/50 HPFs and median tumor size was 14 cm. Their histologic features were similar to gastric GISTs in 22 cases, and to small intestinal GISTs in 6 cases. These tumors were KIT positive 38/41, CD34 positive 20/33, 8 had PDGFRA mutations, and 6 had KIT exon 11 mutations. The median survival was 129 months (range: 0 to 397 mo) and 14 patients were alive at the end of follow-up. Multiple tumor cases showed median mitotic count of 14/50 HPFs and the main tumor median size was 16 cm. The histologic features were similar to small intestinal GISTs in 21 cases and to gastric GISTs in 7 cases; small intestinal attachment or history of a previous small intestinal GIST were noted in 5 cases, whereas no tumor was attached to stomach. The multiple GISTs were KIT positive 23/24, CD34 positive 7/21, and 5 had KIT exon 11 mutations, 3 had KIT exon 9 mutations, and 2 had PDGFRA mutations. The median survival was for 8 months and all patients died. Omental GISTs are clinicopathologically heterogenous. Patients with solitary tumors usually have gastric GIST-like morphology and a better prognosis than those with multiple tumors, whose tumor usually has small intestinal GIST-like histology. Omental GISTs unattached to gastrointestinal tract often resemble gastric GISTs suggesting that they may be gastric GISTs directly extending or parasitically attached into the omentum, whereas multiple omental GISTs more often resemble small intestinal GISTs suggesting that they may be metastatic or detached from this source. KIT positive Cajal cells were not found in normal omental tissues failing to support the presence of these ancestral cells for GIST in the omentum.