peritoneum, mesenetry and retroperitoneal tumors

PERITONEUM, MESENETRY AND RETROPERITONEAL TUMORS

PERITONEUM, MESENETRY AND RETROPERITONEAL TUMORSBYDR. HAYTHAM FAYEDLECTURER OF SURGICAL ONCOLOGYALEXANDRIA FACULTY OF MEDICINE

Surgical Anatomy of the PeritoneumThe peritoneum is the largest serous membrane in the body, with a surface area of about 22,000 cm2.

It can be divided into parietal and visceral portions:

The parietal layer lines the abdominal and pelvic cavities and the abdominal surface of the diaphragm. The visceral layer covers the abdominal and pelvic viscera and includes the mesenteries.

Surgical Anatomy of the PeritoneumThe parietal peritoneum is only loosely connected with the body wall, separated from it by an adipose layer, the tela subserosa;

Whereas the visceral peritoneum is usually tightly attached to the organs it covers.

The peritoneum consists of a fibrous layer (the tunica subserosa) and a surface layer of mesothelium (the tunica serosa).

Surgical Anatomy of the PeritoneumThe peritoneal cavity is a potential space.

It normally contains only a thin film of fluid which lubricates the surfaces, allowing frictionless movements of the gastrointestinal tract.

Under the effects of certain pathologic conditions, great quantities of fluid can occupy the peritoneal cavity.

Surgical Anatomy of the PeritoneumPeritoneum does not line the entirety of the abdominopelvic cavity. It is lifted from the body wall, especially posteriorly, by organs located against the wall during embryologic development.

This chain of events causes the formation of a retroperitoneal space between the peritoneum and the body wall, with organs situated within the space.

An organ that is covered only in part by the peritoneum is referred to as a retroperitoneal organ. An organ that is covered by peritoneum essentially everywhere except for the site of entrance of vessels is referred to as an intraperitoneal organ.

NEOPLASMS OF THE PERITONEUMPrimary malignancies Secondary malignanciesRare Include malignant mesothelioma and sarcomasMost of the casesDue to transperitoneal metastases from a carcinoma of the GIT (especially the stomach, colon, and pancreas), the genitourinary tract (most commonly, ovarian), or more rarely, an extra-abdominal site (e.g., breast).

When metastatic cancer deposits diffusely coat the visceral and parietal peritoneum, these peritoneal metastases are referred to as carcinomatosis.Malignant neoplasms of the peritoneum may be classified as primary or secondary depending on the site of origin of the tumor.

NEOPLASMS OF THE PERITONEUMPrimary peritoneal tumorsClassificationDefined as tumors with primary manifestation in the peritoneum in the absence of a visceral site of origin.

They arise from mesothelial cells, submesothelial mesenchymal cells, and uncommitted stem cellsMesothelial tumorsPeritoneal malignant mesotheliomaWell-differentiated papillary mesotheliomaMulticystic mesotheliomaAdenomatoid tumor

Epithelial tumorsPrimary peritoneal serous carcinomaPrimary peritoneal serous borderline tumor

Smooth muscle tumorLeiomyomatosis peritonealis disseminata

Tumors of uncertain originDesmoplastic small round cell tumorSolitary fibrous tumor

NEOPLASMS OF THE PERITONEUMMalignant Peritoneal Mesothelioma

The most common primary malignant peritoneal neoplasm.

The median survival rate for patients with this rare tumor is 4 to 12 months.

At least in part, this poor prognosis is due to the very advanced stage of the disease at the time of presentation.


Classifying malignant mesotheliomas into diffuse and localized subtypes has prognostic significance.

Diffuse malignant mesotheliomas are highly aggressive and,with a few exceptions such as well-differentiated papillary mesotheliomas that occur in women, are incurable.

In contrast, patients with localized malignant mesotheliomas usually have a good prognosis following complete surgical excision of the lesions


Clinical picture:. Fifty to 70 percent of patients have a history of asbestos exposure.

Other etiologic factors implicated in the development of malignant mesothelioma include exposure to erionite (a mineral fiber found in Turkey), therapeutic irradiation, exposure to simian virus 40, and, in rare cases, chronic pleural or peritoneal irritation. Occasionally, malignant mesothelioma is seen in young patients with no exposure history.

The majority of all malignant mesotheliomas occur in men, with a median age at presentation of 60 years.

In women, peritoneal malignant mesothelioma occurs in a slightly younger age group (mean age, 50 years) and, in general, has a better prognosis.


Clinical picture:. Abdominal pain, ascites, and weight lossGastrointestinal complications such as bowel obstruction may occur with advanced disease. Patients with localized peritoneal malignant mesotheliomas may complain of localized abdominal pain or a palpable abdominal or pelvic mass.The omentum may be diffusely involved with tumor and present as an epigastric mass.


CT demonstrates mesenteric thickening, peritoneal studding, hemorrhage within the tumor, and ascites.

At laparotomy, the ascitic fluid ranges from a serous transudate to a viscous fluid rich in mucopolysaccharides.

The neoplasm tends to involve all peritoneal surfaces, producing large masses of tumor.

In contrast to pseudomyxoma peritonei, local invasion of intra-abdominal organs, such as the liver, intestine, bladder, and abdominal wall, is common.



It may be difficult to differentiate a malignant peritoneal mesothelioma from diffuse peritoneal carcinomatosis arising from an intra-abdominal organ such as the stomach, pancreas, colon, or ovary.

Careful intraoperative examination of the pattern of spread and biopsy with histologic examination allow this distinction to be made.

Furthermore, malignant peritoneal mesothelioma generally remains confined to the abdomen, whereas advanced-stage intra-abdominal carcinomas frequently have pulmonary and other extra-abdominal metastases.

Extension of the mesothelioma into one or both pleural cavities is more likely than hematogenous dissemination.


Complete surgical resection is technically challenging and requires peritonectomy with resection of involved organs.

Combined-modality approaches using surgery and chemotherapy hint of a brighter future.

NEOPLASMS OF THE PERITONEUMWell-differentiated Papillary Mesothelioma

It occurs predominantly in women and most often arises from the peritoneal surfaces of the pelvis, but it has been reported to occur in the pleura, pericardium, and tunica vaginalis.

NEOPLASMS OF THE PERITONEUMMulticystic MesotheliomaMulticystic mesothelioma is an unusual, multilocularcystic tumor that most commonly arises from the pelvic surfaces of the peritoneum.

It has benign or indolent biologic behavior in the majority of patients.

Some authors consider it to be a mesothelial neoplasm because it may recur locally and in rare cases may showmalignant transformation . Other authors believe that it is a non-neoplastic, reactive mesothelial proliferation

NEOPLASMS OF THE PERITONEUMPrimary Peritoneal Serous Carcinoma

Primary peritoneal serous carcinoma is an epithelial tumor that arises from the peritoneum.

At histopathologic analysis, it resembles a malignant ovarian surface epithelial stromal tumor.

Primary peritoneal serous carcinoma is thought to arise from extraovarian mesothelium that has mullerian potential, making it a unique clinicopathologic entity distinct from its ovarian counterpart.

NEOPLASMS OF THE PERITONEUMPrimary Peritoneal Serous Carcinoma

Patients typically present with complaints of abdominal distention, pain, and fullness; increasing abdominal girth; and gastrointestinal symptoms such as nausea and vomiting.

Clinically, the majority of patients have ascites and elevation of serum levels of cancer antigen CA- 125.

NEOPLASMS OF THE PERITONEUMSecondary Tumors and Tumorlike Lesions of the Peritoneum

Tumors and tumor-like lesions that secondarily involve the mesothelial or submesothelial layers of the peritoneum are a diverse group of disorders that range in biologic behavior from benign to highly malignant.

The anatomy of peritoneal ligaments and mesenteries and the normal circulation of peritoneal fluid dictate location and distribution of these diseases within the peritoneal cavity.

NEOPLASMS OF THE PERITONEUMClassification of Secondary Tumors and Tumorlike Lesions of the Peritoneum

I. Metastatic neoplasmsCarcinomatosisPseudomyxoma peritoneiLymphomatosisSarcomatosis

II. Infectious and inflammatory lesionsGranulomatous peritonitisInflammatory pseudotumorSclerosing encapsulating peritonitis

III. Miscellaneous tumors and tumorl-ike lesionsEndometriosisGliomatosis peritoneiOsseous metaplasiaCartilagenous metaplasiaMelanosisSplenosis

NEOPLASMS OF THE PERITONEUMPeritoneal carcinomatosis:

This is a common terminal event in many cases of carcinoma of the stomach, colon, ovary or other abdominal organs and also of the breast and bronchus.

The peritoneum, both parietal and visceral, is studded with secondary growths and the peritoneal cavity becomes filled with clear, straw-colored or blood-stained ascitic fluid.


The main forms of peritoneal metastases are:

Discrete nodules by far the most common variety;Plaques varying in size and colour;Diffuse adhesions this form occurs at a late stage of the disease and gives rise, sometimes, to a frozen pelvis.


Differential diagnosis

Early discrete tubercles common in tuberculous peritonitis are greyish and translucent and closely resemble the discrete nodules of peritoneal carcinomatosis.

Fat necrosis can usually be distinguished from a carcinomatous nodule by its opacity.

Peritoneal hydatids can also simulate malignant disease after rupture of a hydatid cyst, with seeding of daughter cysts.


Treatment

Ascites caused by carcinomatosis of the peritoneum may respond to systemic or intraperitoneal chemotherapy or to endocrine therapy in the case of hormone receptor-positive tumours.

NEOPLASMS OF THE PERITONEUMPseudomyxoma Peritonei

A rare malignant process of the peritoneal cavity that characteristically arises from a ruptured ovarian or appendiceal adenocarcinoma.

The peritoneum becomes coated with a mucus-secreting tumor that fills the peritoneal cavity with tenacious, semisolid mucus and large loculated cystic masses.


Pseudomyxoma peritonei is most prevalent in women between 50 and 70 years of age.

It is often asymptomatic until very late in its course, and patients often experience a global deterioration in their health long before the diagnosis of pseudomyxoma peritonei is made.


Symptoms include abdominal pain and distention as well as numerous nonspecific symptoms.

Physical examination reveals a distended abdomen with non-shifting dullness.

On occasion, a palpable abdominal mass may be present, especially in tumors of appendiceal origin.



CT may demonstrate posterior displacement of the small intestine, loculated collections of fluid-density material, and scalloping of intra-abdominal organs due to extrinsic compression by adjacent peritoneal implants.


The management of these patients includes drainage of the mucus and intraperitoneal fluid and cytoreduction of the primary and secondary tumor implants, including peritonectomy and omentectomy.

For those tumors originating from an appendiceal adenocarcinoma, a right colectomy is also performed.

Ovarian malignancies are treated with total abdominal hysterectomy and bilateral salpingo-oophorectomy as well as cytoreduction.


In the setting of an indeterminate site of origin, a right colectomy and resection of the omentum along with bilateral oophorectomy and cytoreduction surgery are performed.

Postoperative adjuvant therapy has included the use of intraperitoneal 5-fluorouracil, mitomycin C, and oxiliplatin, as well as intraperitoneal mucolytics,

Tumors of the omentumOmental cysts

Pathology

Most cysts of the omentum are of lymphatic mesothelioma origin.

All are rare.


Cystic lymphangioma

In childhood, omental cysts are usually caused by developmental abnormalities of the lymphoid tissue, such as obstruction of the lymphatic channels or by growth of congenitally misplaced lymphatic tissue.

They are variously called chylous cysts, cystic hygromas, or cystic lymphangiomas, and are benign.

They vary greatly in size, and can be unilocular or multilocular.

Histologically each cyst has an endothelial lining similar to cystic hygroma of the neck, and contains many foamy macrophages, giving the fluid a milky appearance.


Cystic mesothelioma

Omental cysts of mesothelial origin occur almost exclusively in adult life, usually in women under the age of 50 years.

Although they are benign, local recurrence often occurs after surgical excision.

They appear as large multicystic masses similar to cystic lymphangiomas, but histologically they are lined by flattened or cuboidal mesothelial cells and the cyst fluid is clear, containing mucopolysaccharides.

Although the aetiology is unknown there is no association with asbestos exposure.


Dermoid cysts

As with dermoid cysts elsewhere in the body, omental dermoid cysts are lined with squamous epithelium and may contain epithelial structures such as hair and teeth.

Pseudocysts

Omental pseudocysts are caused by fat necrosis or abdominal trauma with haematoma formation. They are lined with fibrous tissue and contain blood-stained fluid.

Tumors of the omentumOmental cystsClinical features and treatment

Many omental cysts are small and asymptomatic and may only be discovered incidentally at laparotomy or autopsy.

Large cysts may present with diffuse abdominal distension or as asmooth, mobile, palpable mass in the lower midline. Characteristically they are non-tender unless complicated by torsion of the omentum or intestinal obstruction.

Plain radiographs of the abdomen may demonstrate a soft tissue shadow and barium studies may show displacement of bowel.

The differential diagnosis includes mesenteric, peritoneal, or retroperitoneal cysts and tumours but the diagnosis is usually made at laparotomy.

Treatment consists of surgical excision of the cyst.

Tumors of the omentumSolid tumors of the omentum

Pathology

Secondary tumor

The vast majority of omental neoplasms are metastatic carcinomas arising from ovary, bowel, or pancreas and these are often associated with abdominal ascites.

The rare, diffuse, malignant mesothelioma of the peritoneum which is associated with the exposure to fibrous minerals such as asbestos also consistently involves the omentum.

Tumors of the omentumSolid tumors of the omentumPathologyPrimary tumorPrimary solid tumors of the omentum are exceptionally rare and may be benign or malignant. The majority are of smooth muscle origin. Malignant potential is difficult to predict from the histology but approximately one-third are frankly malignant. Before making a diagnosis of primary smooth muscle tumour of the omentum, leiomyosarcoma of the uterus or gastrointestinal tract giving rise to omental metastases must be carefully excluded. Other rare primary omental tumors include fibroma, fibrosarcoma, lipoma, and liposarcoma. Infantile myxoid hamartomas, found in infants under 1 year old, consist of multiple nodular lesions which show histological resemblance to myxoid liposarcoma; the clinical course is invariably benign.

Tumors of the omentumSolid tumors of the omentum

Clinical features and treatment

Benign primary tumours of the omentum, when sufficiently large, present with a palpable abdominal mass or diffuse distension and require surgical excision.

Malignant primary omental tumours are highly invasive and often present late with involvement of adjacent organs. Radical surgical excision of both the omentum and the involved organs may be required, but often palliative surgery is the only treatment option.

Retroperitoneal neoplasms

The retroperitoneum is a large potential space bounded anteriorly by the posterior peritoneum, posteriorly by the spine and back muscles, superiorly by the diaphragm, inferiorly by the levators, and laterally by the flank muscles at the level of the anterior superior spine of the iliac crest to the tip of the twelfth rib.


In this vast potential space, retroperitoneal masses tend to become very large before producing signs or symptoms, thus accounting for the poor prognosis for most malignant tumors arising there.

Although the pancreas, kidneys, ureters, and adrenals are retroperitoneal structures, neoplasms of these organs are not generally included in the analysis of retroperitoneal neoplasms.


With rare exceptions, retroperitoneal neoplasms are sarcomas, lymphomas, or benign lesions.

Retroperitoneal sarcomas are rare, representing only about 0.1 to 0.2per cent of all malignancies overall and only about 10 to 15per cent of all soft-tissue sarcomas. They form approximately 40per cent of all retroperitoneal masses.

RETRO-PERITONEAL SARCOMA

Retro-peritoneal sarcoma Sarcomas constitute a heterogeneous group of rare solid tumors of mesenchymal cell origin with distinct clinical and pathological features.

They are divided into two broad categories:Soft tissue sarcomasBone sarcomas

Retro-peritoneal sarcoma Sarcomas collectively account for approximately 1% of all adult malignancies and 15% of pediatric malignancies.

The true incidence of STS is underestimated, especially because a large proportion of patients with gastrointestinal stromal tumors (GISTs) may not have been included in tumor registry database before 2001.

Retro-peritoneal sarcoma The most common subtypes of STS are undifferentiated pleomorphic sarcoma, GISTs, liposarcoma, leomyosarcoma, synovial sarcoma and malignant peripheral nerve sheath tumors.

The anatomic site of the primary disease represents an important variable that influences treatment and outcome. Extremities (43%), trunk (10%), visceral(19%), retroperitoneal (15%) and head and neck (9%) are the most common primary sites.

Retro-peritoneal sarcoma Approximately 80 percent of the neoplasms that arise within the retroperitoneal space are malignant.

Furthermore, the majority of patients who present with a primary retroperitoneal, extravisceral, unifocal soft tissue mass will be found to have a sarcoma.

Retro-peritoneal sarcoma In adults, the most common histologic types of retroperitoneal STS are liposarcomas and leiomyosarcomas, followed by pleomorphic undifferentiated sarcoma/malignant fibrous histiocytoma. A variety of other histologic types may be observed, but they are much less common in the retroperitoneum than in other primary sites.

Retro-peritoneal sarcoma Among children, the most common histologic types of retroperitoneal STS are extraskeletal Ewing sarcoma/primitive neuroectodermal tumors [PNET], alveolar rhabdomyosarcoma, and fibrosarcoma

Approximately one-half of all retroperitoneal sarcomas are high-grade tumors, although this varies according to histology. The majority of retroperitoneal liposarcomas are low- to intermediate-grade lesions.

Retro-peritoneal sarcoma STS most commonly metastasize to the lungs ; tumors arising in the abdominal cavity more commonly metastasize to the liver and peritoneum.

Management of STS in adult patients is addressed from the perspective of the following disease subtypes:STS of extremity, superficial/ trunk, or head and neck.Retroperitoneal or intra-abdominal STS.GISTsDesmoid tumorsRabdomyosarcoma.

Retro-peritoneal sarcoma Genetic cancer syndromes with predisposition to STS:

Li-Faumeni syndrome (TP53 germline mutation). Associated with RMS, fibrosarcoma and undifferentiated pleomorphic sarcoma. Gardner syndrome (desmoid tumors)Carney-Stratakis syndrome (GISTs and paragangliomas)

Retro-peritoneal sarcoma WORKUP:Prior to the initiation of therapy, all patients should be evaluated and managed by multidisciplinary team.

History and physical examination.Chest, abdomen and pelvis CT with contrastMRI may add some data

Retro-peritoneal sarcoma WORKUP:

Criteria for unresectabilityRadiographic findings that indicate unresectability include:

Extensive vascular involvement (aorta, vena cava and/or iliac vessels), although involvement of the vena cava and iliac veins is a relative rather than absolute contraindication, as these vessels can often be replaced with interposition grafts

Peritoneal implants

Distant metastases

Involvement of the root of the mesentery (specifically, the superior mesenteric vessels)

Spinal cord involvement

Retro-peritoneal sarcoma WORKUP:

Biopsy:Pre-resection biopsy is not necessarily required ; consider biopsy if there is suspicion of malignancy other than sarcoma.Image-guided (U/s or CT) core needle biopsy is preferred

Patients with personal/family history suggestive of Li-Fraumeni syndrome should be considered for further genetic assessment.

Retro-peritoneal sarcoma Staging:

Retroperitoneal sarcomas are staged using the same TNM system as is used for extremity STS. However, the ability of the TNM staging system to discriminate outcomes is limited.

Several studies have found no prognostic role for tumor size in retroperitoneal sarcoma.

Given the importance of histologic grade and resection margins in the prognosis of retroperitoneal STS, an alternative staging system has been proposed that incorporates these features as well as the presence or absence of metastatic disease. However, this staging system is not in widespread use.

Retro-peritoneal sarcoma Staging:The Dutch/Memorial Sloan-Kettering cancer center classification system for retroperitoneal soft tissue sarcomas

ClassificationDefinitionStage ILow-grade, complete resection, no metastasesStage IIHigh-grade, complete resection, no metastasesStage IIIAny grade, incomplete resection, no metastasesStage IVAny grade, any resection, distant metastases

Retro-peritoneal sarcoma TREATMENTSurgical resection:Surgical resection has traditionally been the only potentially curative treatment for a localized retroperitoneal STS.

The ability to perform a complete surgical resection at the time of initial presentation is the most important prognostic factor for survival.

The usual reasons for unresectability are extensive vascular involvement or the presence of multiple peritoneal implants.

Retro-peritoneal sarcoma TREATMENTSurgical resection:The primary oncologic goal is complete resection with microscopically negative margins (R0 resection).

However, the large size of most retroperitoneal tumors, coupled with the inability to obtain wide margins due to anatomic constraints make this goal difficult to achieve.

In clinical practice, many resections are grossly complete but with microscopically positive margins (R1 resection)

Retro-peritoneal sarcoma TREATMENTSurgical resection:Resection of adjacent organs such as the small bowel, colon or kidney is often required to achieve a complete resection and bowel preparation and evaluation of kidney function should be performed prior to exploration.

Liberal en-bloc resection of adjacent viscera may allow a subset of patients to achieve wide, macroscopically negative surgical margins who might otherwise have been considered unresectable.

Retro-peritoneal sarcoma TREATMENTSurgical resection:Role of debulking surgeryThere is no survival benefit for incomplete resection (a "debulking" procedure) in patients with unresectable retroperitoneal STS.

Retro-peritoneal sarcoma TREATMENTAdjunctive RT:

In contrast to extremity STS in which the most common site of first recurrence is a distant site, the primary pattern of treatment failure after resection of a retroperitoneal STS is local.

Adjunctive radiation therapy (RT) can be administered following resection (adjuvant RT). However, increasingly, preoperative RT is being chosen for large high-grade or intermediate-grade STS.


Adjuvant RT

It is often difficult to deliver postoperative radiation therapy because the bowel and other organs fall into the resection cavity; however, newer techniques such as intensity-modulated RT (IMRT) and proton beam irradiation make it more feasible but the therapeutic ratio is probably still more favorable with preoperative RT.

Nevertheless, it is reasonable to consider the use of postoperative RT if it can be delivered safely.


Adjuvant RT

In the postoperative setting, radiation doses to the tumor bed are often limited by the large field size and the proximity and tolerance of surrounding radiosensitive normal structures, such as the liver and bowel.

In fact, many multidisciplinary sarcoma groups do not routinely offer postoperative RT to patients with resected retroperitoneal sarcomas because of significant concerns about the narrow therapeutic ratio.


Preoperative RT

The delivery of RT prior to surgery, with or without intraoperative RT (IORT) at the time of resection, may permit the safe delivery of higher RT doses than are possible in the postoperative setting


Preoperative RT

There are several theoretical advantages for preoperative as compared to postoperative RT for retroperitoneal STS :

The main advantage of preoperative RT is that the gross tumor volume can be precisely defined for radiation treatment planning, allowing accurate targeting of the radiation volume around the tumor.

The tumor itself can act to displace small bowel from the high-dose radiation field, resulting in safer and less toxic treatment.


Preoperative RT


Higher RT doses can be delivered to the actual tumor field, since bowel adhesions to tumor are less likely compared to the postoperative setting.

The risk of intraperitoneal tumor dissemination at the time of the operation may be reduced by preoperative RT.


Preoperative RT


Radiation is considered to be biologically more effective in the preoperative setting.

It is possible that an initially unresectable tumor may be converted to one that is potentially resectable for cure.

These advantages may result in an improvement in the therapeutic ratio when RT is administered preoperatively.

Retro-peritoneal sarcoma Outcomes and prognostic factors

Retroperitoneal sarcomas have a substantially less satisfactory outcome than soft tissue sarcomas (STS) at other sites, such as the extremities or trunk.

Several factors contribute to poor outcome and a high rate of recurrence:

Retroperitoneal STS are often large at diagnosis and anatomically situated such that wide resection is often not achievable.

Even with complete resection, retroperitoneal liposarcomas tend to do worse than extremity liposarcomas, independent of tumor size, grade, or surgical margin.


Retroperitoneal sarcomas have a substantially less satisfactory outcome than soft tissue sarcomas (STS) at other sites, such as the extremities or trunk.

Several factors contribute to poor outcome and a high rate of recurrence:

The surrounding normal tissues (liver, kidney, gastrointestinal tract, spinal cord) have relatively low tolerance for radiation therapy (RT). As a result, radiation dose levels must be kept below those typically employed for extremity sarcomas.


In contrast to extremity sarcomas, 90 percent of first recurrences are local. Eventually, distant metastases develop in 20 to 30 percent . The main sites of distant metastases are liver and lungs.

Local recurrence rates are higher with high-grade (poorly differentiated) tumors, liposarcoma histology, and in patients with positive resection margins.


In contrast to extremity sarcomas, 90 percent of first recurrences are local. Eventually, distant metastases develop in 20 to 30 percent . The main sites of distant metastases are liver and lungs.

Local recurrence rates are higher with high-grade (poorly differentiated) tumors, liposarcoma histology, and in patients with positive resection margins.

Retro-peritoneal sarcoma

Recurrent retroperitoneal sarcoma





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peritoneum, mesenetry and retroperitoneal tumors

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