Malignant extragastrointestinal stromal tumor: A challenging diagnosis due to unusual presentation

Abhay Vilas Deshmukh; Swati Dhanraj Hagone; Vitaladevuni Balasubramanyam Shivkumar; Nitin M Gangane

doi:10.4103/jmedsci.jmedsci_131_21

CASE REPORT

Year : 2022 | Volume : 42 | Issue : 4 | Page : 187-190

Malignant extragastrointestinal stromal tumor: A challenging diagnosis due to unusual presentation

Abhay Vilas Deshmukh, Swati Dhanraj Hagone, Vitaladevuni Balasubramanyam Shivkumar, Nitin M Gangane
Department of Pathology, Mahatma Gandhi Institute of Medical Sciences, Wardha, Maharashtra, India

Date of Submission	21-Apr-2021
Date of Decision	22-May-2021
Date of Acceptance	26-May-2021
Date of Web Publication	23-Jul-2021

Correspondence Address:
Prof. Vitaladevuni Balasubramanyam Shivkumar
Department of Pathology, Mahatma Gandhi Institute of Medical Sciences, Sevagram, Wardha - 442 102, Maharashtra
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/jmedsci.jmedsci_131_21

Abstract

Gastrointestinal stromal tumors are the most common mesenchymal tumors of gastrointestinal tract which comprise <1% of all primary gastrointestinal malignancies. These tumors show mutations in the KIT gene or platelet-derived growth factor receptor-A gene and usually stains positively for CD117. Very few cases of extragastrointestinal GIST (EGIST) have been reported in literature which originate from omentum and mesentery as per our knowledge. Here, we report a case of EGIST arising from omentum with no connection to gastrointestinal tract organs in a 60-year-old woman who presented with abdominal pain for 2–3 months. Intraoperative findings showed the presence of multiple globular masses and nodules in the peritoneal cavity. Microscopically, the spindled tumor cells were arranged in interlacing fashion. Immunohistochemistry showed positivity for CD117 and negativity for smooth muscle actin (SMA). Thus, EGIST should always be considered as a differential diagnosis for nodular mesenteric masses.

Keywords: Malignant extragastrointestinal stromal tumor, CD117, cell of Cajal, imatinib

How to cite this article:
Deshmukh AV, Hagone SD, Shivkumar VB, Gangane NM. Malignant extragastrointestinal stromal tumor: A challenging diagnosis due to unusual presentation. J Med Sci 2022;42:187-90

How to cite this URL:
Deshmukh AV, Hagone SD, Shivkumar VB, Gangane NM. Malignant extragastrointestinal stromal tumor: A challenging diagnosis due to unusual presentation. J Med Sci [serial online] 2022 [cited 2023 May 31];42:187-90. Available from: https://www.jmedscindmc.com/text.asp?2022/42/4/187/353042

Introduction

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of gastrointestinal tract and comprise <1% of all primary gastrointestinal malignancies.^[1] These tumors show mutations in the KIT gene or platelet-derived growth factor receptor-A gene and may or may not stain positively for KIT.^[2] Most GISTs arise from the stomach (50%–70%), small intestine (20%–30%), large intestine (5%), and esophagus (5%).^[3]

Extragastrointestinal GISTs (EGISTs) are tumors which are not connected to the gastrointestinal tract. There are very few cases of EGISTs reported in literature which originate from omentum and mesentery.^[4] EGISTs arising from the omentum are usually extremely rare and their clinicopathological behavior is poorly known. Here, we report a case of EGIST arising from omentum with no connection to gastrointestinal tract organs in a 60-year-old woman.

Case Report

A 60-year-old postmenopausal woman presented to Obstetrics and Gynaecology Outpatient Department at Mahatma Gandhi Institute of Medical Sciences, Sevagram, Wardha, Maharashtra, India, a tertiary care hospital in Central India with complaints of pain in the abdomen for 2–3 months. Physical examination was unremarkable. Contrast-enhanced computed tomography abdomen and pelvis revealed multiple deposits in peritoneum and omentum, each measuring around 1 cm × 1 cm–2 cm × 2 cm in the area superior to the uterus [Figure 1]. The rest organs and cavity were unremarkable, there was no lymphadenopathy. The routine hematological investigations were normal. A possibility of metastatic deposits in the abdomen was raised. The patient was investigated thoroughly to look for primary elsewhere in the body. Whole-body 18-fluorodeoxyglucose positron emission tomography showed metabolically active lesion in the peritoneal cavity. No other lesion was noted in the whole body.

Figure 1: Computed tomography abdomen image showing the presence of multiple deposits in the peritoneal cavity

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Exploratory laparotomy was performed. On opening abdomen, the surgeon found the presence of multiple globular masses and nodules in the peritoneal cavity. The nodules were adherent to bowel loops. These were gently separated. Rest of the organs in the abdominal cavity was unremarkable. As no primary lesion seen in the abdominal organs, only partial omentectomy was done. The specimen was sent to surgical pathology section for examination. Grossly, the omentum was a gray yellow fibrofatty tissue piece having the presence of multiple gray-white nodular masses. The nodules were variable in sizes, from 0.5 cm × 0.5 cm × 0.5 cm to 3 cm × 2 cm × 1 cm in size. Cut surface was gray white [Figure 2]. Microscopically, the tumor cells were arranged in interlacing fashion. The individual tumor cells were spindle shaped and showed moderate nuclear atypia. The mitotic count was 1–2/10 hpf [Figure 3]. Immunohistochemistry (IHC) was done using a formalin-fixed and paraffin-embedded tissue blocks. The tumor cells were found to be positive for CD117, c-kit (YR145) (1:100, rabbit monoclonal primary antibody, CMC11731050, clone: 117R-14-ASR0, cell marque) [Figure 4], while it was negative for smooth muscle actin (1A4) (1:100, mouse monoclonal antibody, clone: 202M-94, cell marque) [Figure 5]. A diagnosis of malignant GIST arising from omentum was made. She was started on adjuvant imatinib therapy in view of intermediate risk and is disease free at 10 months.

Figure 2: Gross appearance of tumor mass showing multiple gray-white nodules attached to mesentery

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Figure 3: Microscopic view showing spindled tumor cells arranged in interlacing fashion. The individual tumor cells were spindle-shaped cells showing moderate nuclear atypia (H and E, magnification = ×100)

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Figure 4: Immunohistochemistry showing CD117 positivity in tumor cells (magnification = ×400)

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Figure 5: Immunohistochemistry showing SMA negativity in tumor cells (magnification = ×400)

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Discussion

GISTs are mesenchymal tumors which arise from the interstitial cell of Cajal or related stem cell precursors.^[5] EGISTs comprise approximately 5%–10% of all GISTs.^[6] The diagnosis of EGIST in our case was made by morphology including gross appearance, microscopic findings, and IHC. Literature shows reports of EGIST at few sites such as omentum, retroperitoneum, pancreas, liver, pleura, bladder, adrenal gland, and prostate till date.^[4],[5],[6]

IHC plays an important role in the diagnosis of EGISTs using a complete panel of antibodies for mesenchymal tumors. >90% of GISTs show overexpression of the receptor tyrosine kinase KIT (CD117) gene.^[7] Approximately 70% GISTs express CD34 marker and may also express SMA on IHC.^[8] Other commonly used markers to differentiate GIST from other entities include S-100, caldesmon, and cytokeratin which can show variable immunoreactivity.^[8] The differential diagnoses for GIST include inflammatory myofibroblastic tumor (negative for CD117 and CD34), tumors with nervous differentiation such as gastric schwannomas (positive for S-100 and negative for CD117), and tumors with fibrous differentiation such as intrabdominal fibromatosis (CD117 negative). The CD117 positive tumors can be differentiated with the help of IHC including metastases of malignant melanoma (HMB45 and Melan A-positive) and angiosarcoma (CD31 positive). Most reliable criteria for distinguishing malignant GISTs are tumor ≥5 cm in size showing mitotic rate of 5/50 high power fields or more on microscopy.^[9]

Reith et al., coined the term “EGIST” in 2000 for tumors which occur in soft tissues of the abdomen. He described these tumors histologically and immunophenotypically similar to that of GISTs.^[10] Most EGISTs arise from mesentery, omentum, and retroperitoneum.^[11] These tumors are well defined, encapsulated, gray white, and firm in consistency. Cut surface is usually homogenous in small lesions, while large specimen may show the presence of hemorrhage, necrosis, and cystic degeneration.^[7] Microscopically, these tumors show moderate to high cellularity. The tumor cells are usually spindle shaped but can also show pleomorphic, epithelioid, or oncocytic variants.^[3],[4],[7]

Clinical features usually depend on the location and size of tumor. Small size EGISTs are discovered incidentally during endoscopy or imaging studies. Symptoms vary depending on the size and location of the tumor-like abdominal mass, pain, discomfort, and distention of the abdomen.^[7],[9] These tumors generally metastasize to the liver (65%) or disseminate in peritoneal cavity (21%) but lymph nodes are usually spared.^[5] In our case, we found multiple nodules and globular masses adherent to bowel loops within the peritoneal cavity.

The current form of management for these tumors includes surgical resection and debulking of tumors along with the removal of adjacent structures which are infiltrated by tumor. The introduction of adjuvant-specific tyrosine kinase inhibitors such as imatinib mesylate is considered as the standard treatment in such patients at present, in spite of high recurrence rate and development of resistance to it.^{[5],[7],[9],[11]} Our patient underwent debulking surgery and was started on adjuvant imatinib therapy in view of intermediate risk. She is now disease free at 8 months.

Conclusion

We present a rare case of EGIST in an elderly woman, presented with vague abdominal pain. It should always be considered as a differential diagnosis for nodular mesenteric masses. As it is a very rare tumor, further studies are required with large sample size and long-term follow-up to decide the management and follow-up of this rare tumor.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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