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Year : 2012  |  Volume : 55  |  Issue : 3  |  Page : 395-398
Retroperitoneal sclerosing PEComa with melanin pigmentation and granulomatous inflammation-A rare association within an uncommon tumor

Department of Pathology, Tata Memorial Hospital, Parel, Mumbai, India

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Date of Web Publication29-Sep-2012


PEComa, defined as a perivascular epithelioid cell tumor, displays a wide clinicopathological spectrum. Lately, a sclerosing PEComa has been identified as its distinct variant, but with limited documentation, in view of its rarity. Herein, we describe an uncommon case of a 53-year-old lady, who was referred to us with pain abdomen. Radiological imaging disclosed a well-defined, hypodense retroperitoneal mass. The excised tumor was a round, encapsulated soft tissue mass measuring 7 cm with a tan-brown cut surface. Microscopy showed uniform, epithelioid cells with clear cytoplasm, focal melanin pigmentation and mild nuclear atypia, arranged in sheets and nests around capillary-sized vessels in a dense sclerotic stroma. Additionally, co-existing epithelioid granulomas were noted. On immunohistochemistry (IHC), tumor cells were diffusely positive for HMB45; focally for desmin and smooth muscle actin (SMA), while negative for EMA, CD10, S100-P, Melan A, CD34, AMACR and CK MNF116. This case reinforces sclerosing PEComa as an uncommon, but a distinct clinicopathological entity and exemplifies diagnostic challenge associated with it; necessitating application of IHC markers for its correct identification. Presence of melanin pigment and granulomatous inflammation in the present tumor constitute as novel histopathological findings in a sclerosing PEComa.

Keywords: HMB45, melanoma, myomelanocytic tumor, PEComa, retroperitoneal sarcomas, sclerosing PEComa, uncommon soft tissue tumors

How to cite this article:
Rekhi B, Sable M, Desai SB. Retroperitoneal sclerosing PEComa with melanin pigmentation and granulomatous inflammation-A rare association within an uncommon tumor . Indian J Pathol Microbiol 2012;55:395-8

How to cite this URL:
Rekhi B, Sable M, Desai SB. Retroperitoneal sclerosing PEComa with melanin pigmentation and granulomatous inflammation-A rare association within an uncommon tumor . Indian J Pathol Microbiol [serial online] 2012 [cited 2022 Jul 7];55:395-8. Available from: https://www.ijpmonline.org/text.asp?2012/55/3/395/101757

   Introduction Top

PEComas comprise a group of uncommon mesenchymal tumors known to arise from the perivascular epithelioid cells (PEC). This tumor was first described by Bonneti et al.[1] and subsequently termed as PEComa by Zamboni et al.[2] According to the World health organization (WHO) classification of soft tissue tumors, PEComa is a mesenchymal tumor that arises from a histologically and immunohistochemically distinct PEC, which is an undifferentiated cell of neural crest origin, displays a melanocytic and smooth muscle phenotype and objectively diagnosed with immunohistochemical antibody markers like human melanoma black (HMB)-45 and Melan A, along with desmin and smooth muscle actin (SMA), respectively. PEComas include angiomyolipomas (AML) of the kidney and liver, clear cell ''sugar'' tumors of the lung (CCST), lymphangioleiomyomatosis (LAM), along with a group of similar tumors occurring in the soft tissues, visceral organs, like heart, pancreas, rectum, uterus, abdominal serosa and skin. [3]

Within the histomorphological spectrum of PEComas, a small subset of cases with a predilection for retroperitoneum, in women, displays abundant stromal hyalinization, on histopathology, namely sclerosing PEComas, as first described by Hornick et al.[4] Herein, we describe this rare and distinctive variant of PEComa that additionally displayed melanin pigment within and co-existing epithelioid granulomas. Such a histopathological association has not been documented to the best of our knowledge.

   Case Report Top

A 56-year-old-lady referred with upper abdominal pain accompanied with abdominal distention at another hospital. She denied history of cough and or breathlessness. On clinical examination, her vitals were stable. Mild tenderness was noted in her epigastric region. Thereafter, she underwent radiological evaluation, followed by a laparotomy.

Radiological Findings

Ultrasonography (USG) abdomen disclosed a well-defined, round hypoechoic mass measuring 5.0 cm in diameter, in the epigastric region with enlarged porta hepatic lymph nodes. Computed tomography (CT) scan showed a well-defined, round, hypodense mass measuring 7.3 x 6.5 cm, in the right-sided retroperitoneum, extending superiorly up to inferior border of liver, porta and gall bladder fossa and caudally up to renal hilum, displacing pancreatic head superolaterally, and resting on the segment of inferior vena cava, with minimal extensions in the aortocaval region. Abdominal viscera, including bilateral kidneys and adrenals were unremarkable.

Subsequently, she underwent an exploratory laparotomy. Intraoperatively, a discrete, well-circumscribed, circular mass was seen in the retroperitoneum, unattached with the kidneys and adrenals. The mass was excised and submitted for histopathological evaluation.

Histopathological Findings

Grossly, the tumor was well-circumscribed, encapsulated and measured 7.0 x 6.5 x 6.0 cm. Cut surface was tan-brown with focal whitish myxoid areas and calcifications. Necrosis was absent [Figure 1].
Figure 1: Gross Findings. Well-circumscribed, encapsulated tumor measuring 7 cm in diameter with a tan-brown cut surface and focal translucent areas

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On microscopic examination of several sections, a well-circumscribed tumor was noted composed of nests and sheets of uniform polygonal/epithelioid cells with perivascular arrangement, embedded in a sclerotic stroma. Tumor cells displayed mild to moderate nuclear atypia, inconspicuous nucleoli and abundant clear cytoplasm. Mitotic figures and necrosis were absent. In addition, multiple non-necrotizing granulomas with Langhan's giant cells were noted in the tumor vicinity, along with "black" pigment and areas of dystrophic calcifications. Differential diagnoses considered were clear cell carcinoma, clear cell sarcoma or melanoma of soft parts and sclerosing PEComa. Special stain (Masson Fontana) confirmed presence of intracytoplasmic melanin pigment. On immunohistochemical (IHC) staining, tumor cells were diffusely positive for Human melanoma black (HMB)-45 and focally, discretely for desmin and smooth muscle actin (SMA), while negative for cytokeratin (CK MNF116), epithelial membrane antigen (EMA), CD10, AMACR, Melan A, S100-P, and INI-1. Diagnosis of sclerosing PEComa was offered. Special stains for acid fast bacilli (Ziehl-Neelsen) and fungal organisms (Gomori methenamine silver and periodic acid-Schiff) were negative. [Figure 2] and [Figure 3].
Figure 2: Histopathological findings. (a) Nests of clear cells with interspersed 'black' pigment, embedded in sclerotic stroma. (hematoxylin and eosin, x100). (b) Higher magnifi cation, displaying nests of tumor cells with clear cytoplasm, separated by delicate vasculature. (hematoxylin and eosin, x400). (c) Tumor cells with coexisting 'pale' areas containing epithelioid granulomas (arrow heads). (hematoxylin and eosin, x200). (d) Epithelioid cell granuloma with a Langhan's giant cell (arrow head). (hematoxylin and eosin, x400)

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Figure 3: (a) Positive staining for melanin pigment within tumor cells embedded in a dense sclerotic stroma. Masson Fontana ×200. (b) Diff use HMB-45 positive tumor cells. (Diaminobenzidine, ×200). (c) HMB-45 positivity within tumor cells, on higher magnifi cation (Diaminobenzidine, ×400). (d) Focal desmin positivity within tumor cells (arrow heads). DAB ×200. Inset showing discrete tumor cells positive for desmin. (Diaminobenzidine, ×400)

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   Discussion Top

PEComa is a relatively uncommon, invariably benign soft tissue tumor with a wide clinicopathological spectrum, along with its borderline and malignant counterparts that are rarer. [1],[2],[3] Sclerosing PEComa is a recently described distinctive variant of a PEComa, most commonly identified in the pararenal retroperitoneum of middle-aged women and on histopathology, displays tumor cells within dense stromal hyalinization. [3] To the best of our knowledge, very few cases of a sclerosing PEComa have been documented in literature, including none exhibiting pigmentation and or coexisting granulomas, as the present case of a lady, who presented with pain and distention in abdomen. [4],[5],[6],[7] [Table 1] shows literature review of previously documented cases of a sclerosing PEComa.
Table 1: Literature review of sclerosing PEComas

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Variable symptomatology has been noted in cases of sclerosing PEComas, most commonly pain abdomen, followed by pressure sensation and diarrhea. [3],[4] Imaging in the present case unraveled a discrete, round retroperitoneal mass, unattached to any visceral organs.

Grossly, a well-circumscribed, round soft tissue mass was received with a characteristic tan-brown cut surface and focal calcifications, as similarly noted in earlier descriptions. [4],[6] On histopathology, nests of polygonal/epithelioid tumor cells with clear cytoplasm, arranged in an organoid pattern, characteristically around blood vessels, within a hyalinized matrix, led to consideration of differential diagnoses, including renal cell carcinoma, melanoma and an adrenal neoplasm. Lack of a renal mass, with EMA, CD10 and alpha-methylacyl-CoA racemase (AMACR) negativity, on IHC, ruled out a renal cell carcinoma, despite clear cells. Considering age of the patient, negative expression of cytokeratin and lack of association with any of the visceral organs, ruled out other carcinomas. Aforementioned features and IHC profile similarly ruled out an adrenal neoplasm. Earlier, Hornick et al.[4] studied and identified extensive stromal hyalinization in 19% PEComas that they designated as sclerosing PEComas. All these tumors occurred in women, mostly in retroperitoneum, exceeded 5 cm in size, in concert with subsequently documented three similar case reports and followed by the present one. [5],[6],[7] Out of 16 previously documented sclerosing PEComas, only two tumors were reported as malignant. Although tumor size in the present case and most of such cases exceeded 5 cm, other features for malignancy, namely tumor necrosis, pleomorphism, mitotic counts, higher nuclear grade and cellularity were absent. [8] Despite large size, these tumors usually show an indolent course with fewer chances of malignant transformation and metastases. [4] Presence of melanin pigment in our case pigment led to possibility of a melanoma. Melanin pigment is rarely documented in PEComas and none in the sclerosing subtype, so far. [4],[5],[6],[7] S100-P negativity, despite HMB-45 positivity with coexpression of SMA and desmin, led to diagnosis of a PEComa in this case, over a clear cell melanoma. In this way, IHC is necessary for an objective diagnosis of this rare tumor. Apart from aforementioned melanoma-related and smooth muscle markers, other IHC markers expressed in PEComas include microphthalmia transcription factor (MiTF) and TFE3, the latter observed in alveolar soft part sarcomas, translocation related renal cell carcinomas and some other tumors, leading to inclusion of a PEComa in "TFE3-related" tumors. [8],[9] Additional finding noted in the present tumor was multiple granulomas that have never been documented in a PEComa. Their presence can be attributed to mycobacterial infection, considering tuberculosis is endemic in our country. However, special stain for acid-fast bacilli was negative. Moreover, the patient did not reveal any associated pulmonary symptoms. The other possibility considered was coexisting fungal infection that was ruled out with negative results of special stains for fungal organisms. The most likely reason in the present case was tumor-related sarcoidal reaction.

Therapeutically, in view of its benign nature in most cases, a sclerosing PEComa is optimally treated with surgical excision, as noted earlier. [4],[5],[6],[7] Outcomes of this uncommon tumor subtype have been favorable in most cases, except in occasional cases with malignant transformation that were accompanied with tumor recurrence, metastasis and death. [4] Our patient is presently disease-free and on follow-up.

To sum up, the present case reinforces sclerosing PEComa as a distinct clinicopathological variant of a PEComa and exemplifies diagnostic challenge associated with it that necessitates application of various IHC markers for its correct identification from among its differentials. Presence of melanin pigment and granulomatous inflammation in the present tumor are novel findings in a sclerosing PEComa, adding to its histopathological spectrum.

   References Top

1.Bonetti F, Pea M, Martignoni G, Zamboni G. PEC and Sugar. Am J Surg Pathol 1992;16:307-8.  Back to cited text no. 1
2.Zamboni G, Pea M, Martifnoni G, Zancanaro C, Faccioli G, Gilioli E, et al. Clear cell "sugar" tumor of pancreas: A novel member of family of lesions characterized by the presence of perivascular epitheliod cells. Am J Surg Pathol 1996;20:722-30.  Back to cited text no. 2
3.Folpe A. Neoplasms with pervascular epithelioid cell differentiation. In, Fletcher CD, Unni KK, Mertens F, editors. World Health Organization Classification of Tumours: Pathology and Genetics of Tumours of Soft Tissue and Bone. Lyon, France: IARC Press; 2002. p. 221-2.  Back to cited text no. 3
4.Hornick JL, Fletcher CD. Sclerosing PEComa: Clinicopathologic analysis of a distinctive variant with a predilection for the retroperitoneum. Am J Surg Pathol 2008;32:493-501.  Back to cited text no. 4
5.Ramaiah S, Ganesan R, Mangham DC, McNally O, Klys HS, Hirschowitz L. Malignant variant of sclerosing perivascular epithelioid cell tumor arising in the adnexa. Int J Gynecol Pathol 2009;28:589-93.  Back to cited text no. 5
6.Yamada Y, Yamamoto H, Ohishi Y, Nishiyama K, Fukuhara M, Saitou T, et al. Sclerosing variant of perivascular epithelioid cell tumor in the female genital organs. Pathol Int 2011;61:768-72.  Back to cited text no. 6
7.Valiathan M, Sunil BP, Rao L, Geetha V, Hedge P. Sclerosing PEComa: A Histologic Surprise. African J Urol 2011;17:97-100.  Back to cited text no. 7
8.Folpe AL, Mentzel T, Lehr HA, Fisher C, Balzer BL, Weiss SW. Perivascular epitheliod cell neoplasms of soft tissue and gynecologic origin: A clinicopathologic study of 26 cases and review of the literature. Am J Surg Pathol 2005;29:1558-75.  Back to cited text no. 8
9.Rekhi B, Ingle A, Agarwal M, Puri A, Laskar S, Jambhekar NA. Alveolar Soft Part Sarcoma "Revisited"-Clinicopathological Review of 47 cases from a Tertiary Cancer Referral centre, including Immunohistochemical Expression of TFE3 in 22 cases and 21 other Tumors. Pathology 2012;44:11-17.  Back to cited text no. 9

Correspondence Address:
Bharat Rekhi
Department of Pathology, Tata Memorial Hospital, Dr. E.B. Road, Parel, Mumbai-400 012
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0377-4929.101757

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  [Figure 1], [Figure 2], [Figure 3]

  [Table 1]

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