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Abstract

Primary retroperitoneal mucinous cystic neoplasms are rare retroperitoneal tumors, which are histologically similar to mucinous cystic neoplasms of the ovaries. Only 31 cases of primary retroperitoneal mucinous cystic neoplasm with borderline malignancy (PRMCN-BM) have been reported (26 in women and five in men). We describe an additional male patient with PRMCN-BM. A 39-year-old man presented to our hospital with back pain. Twelve years earlier, he had undergone an orchiectomy for a germ cell tumor. Computed tomography showed a 6.9- × 4.4-cm cystic mass in the left pararenal space. Laparoscopic mass excision was performed, and a unilocular cystic mass was found in the pararenal space near the lower pole of the left kidney. A histopathological examination showed a cyst lined by atypical mucinous intestinal epithelium without stromal invasion. Targeted next-generation sequencing identified two hotspot mutations, with one each in the KRAS and GNAS genes. Outpatient follow-up 10 months after surgery showed no evidence of tumor recurrence. PRMCNs are extremely rare retroperitoneal neoplasms, especially in men. These neoplasms are rarely considered in the differential diagnosis of retroperitoneal masses, and their preoperative diagnosis is difficult. Evaluation of additional patients is required to better determine the prognosis of PRMCNs and the optimal postoperative follow-up.

Keywords

Primary retroperitoneal mucinous cystic neoplasm borderline malignancy retroperitoneum case report

Introduction

Primary retroperitoneal mucinous cystic neoplasms (PRMCNs) are rare retroperitoneal tumors that predominantly occur in women.¹ Histologically, PRMCNs resemble ovarian mucinous tumors and are similarly classified into the following three categories: retroperitoneal mucinous cystadenoma, PRMCN with borderline malignancy (PRMCN-BM), and malignant retroperitoneal mucinous cystadenocarcinoma.² PRMCN-BM is exceedingly rare, with only 31 (26 in women and 5 in men) cases described in the literature to date. The preoperative diagnosis of PRMCN-BM is challenging, and its pathogenesis, clinical behavior, and management remain unclear because of the small number of registered cases and the absence of pathognomonic clinical and imaging features.³ The present report describes the sixth case of PRMCN-BM in a male patient and reviews the published data.

Case report

A 39-year-old man presented to our hospital with the complaint of back pain. Twelve years previously, he had undergone an orchiectomy for seminoma at another hospital, and this was followed by four cycles of cisplatin and etoposide chemotherapy. Seven months later, he was transferred to our hospital for follow-up, at which time an abdominal computed tomography (CT) scan was taken. There were no abnormalities, except for the previous orchiectomy site (Figure. 1). He was followed up in our hospital, and there was no recurrence for 12 years.

Figure 1.

Abdominal and pelvic computed tomography scan performed after orchiectomy shows no abnormalities in the retroperitoneum.

On the basis of the history of the testicular tumor, the patient underwent blood tests for tumor markers, such as alpha-fetoprotein and β-human chorionic gonadotropin, but the results were normal. An abdominal and pelvic CT scan showed a 6.9- × 4.4-cm cystic mass in the left pararenal space (Figure 2a–c). No mural nodules were found on the mass, and there were no signs of peritoneal implants, ascites, or lymphadenopathy.

Figure 2.

Unenhanced computed tomography scan of the abdomen and pelvis in the axial plane (a) contrast-enhanced images in the axial (b) and coronal planes and (c) show a 6.9- × 4.4-cm homogeneous cystic mass with smooth borders in the left pararenal space.

The neoplastic nature of the mass was uncertain. Therefore, the patient underwent laparoscopic excision of the mass. The mass was located in the pararenal space near the lower pole of the left kidney. After careful dissection of the pararenal fat and surrounding structures, the cyst was extracted gently without spillage of contents. No bag was used for retrieval, and the cyst was not aspirated before extraction. A gross examination of the surgically resected specimen showed a previously disrupted unilocular cyst (5.9 × 4.4 × 3.5 cm) containing mucinous material and evidence of hemorrhage. The inner surface of the cyst was smooth with no mural nodules or papillae. The entire cyst wall was tan-yellow to gray in color. A histopathological examination showed that the cyst wall was lined by atypical mucinous epithelium of the intestinal type, consisting of columnar and goblet cells, without stromal invasion. The cyst wall showed focal calcification, with pools of extravasated mucin. The epithelium displayed slightly atypical proliferation with glandular budding, tufting of the epithelium, and stratification two to three cells thick. The tumor cells displayed mild-to-moderate nuclear atypia without mitoses (Figure 3a). The epithelial lining showed an intestinal phenotype with positive staining for cytokeratin (CK)7, CK20, and CDX2 (Figure 3b–d). Immunohistochemical staining for c-kit and D2-40 was negative. Pathologically, this tumor was similar to mucinous borderline tumors observed in the ovaries. A subsequent thorough workup for any primary tumors failed to identify other lesions in this patient. Therefore, he was diagnosed with a PRMCN-BM.

Figure 3.

Histological staining of the tumor sample. (a) Hematoxylin and eosin staining shows the cyst wall with intestinal-type mucinous epithelium and focal nuclear stratification. Papillary tufts with mild cytological atypia can occasionally be seen (original magnification, ×100). (b–d) Staining with antibodies to (b) cytokeratin (CK)7, (c) CK20, and (d) CDX2 shows that the epithelial lining is strongly positive for all three (original magnification, ×100).

The tumor DNA was subjected to targeted next-generation sequencing. Libraries were prepared using Oncomine Comprehensive Assay Plus (Thermo Fisher Scientific, Waltham, MA, USA), and the products were sequenced on the Ion S5 System (Thermo Fisher Scientific). Sequencing data were analyzed using Ion Reporter 5.18. Next-generation sequencing identified two missense mutations, which comprised a c.183A>C (p.Gln61His) missense mutation in exon 3 of the KRAS gene and a c.602G>A (p.Arg201His) missense mutation in exon 8 of the GNAS gene.

We followed the patient with CT examinations at 3 and 10 months after surgery. During this period, the patient remained alive, with no evidence of tumor recurrence.

The reporting of this study conforms to the CARE guidelines.⁴

Discussion

PRMCNs are extremely rare retroperitoneal neoplasms, and are histologically similar to mucinous cystic neoplasms of the ovaries. To date, only 31 confirmed cases of PRMCN-BM have been reported (Table 1), with 26 in women and five in men.^3,5–24 The first male patient with PRMCN was described in 1994, with only five additional cases of PRMCN-BM in men, including the present patient, reported since this time.^{7,12,17,18,23}

Table 1.

Clinical features of previously reported cases of PRMCN with borderline malignancy

Case	Year	Reference	Age (years)	Sex	Location	Size (cm)	Clinical symptoms	Preoperative tumor-specific antigen	Imaging features	Gross features	Final diagnosis	Operative method	Outcome
1	1987	Nagata¹⁸	41	F	ND	12 × 10 × 9	Abdominal pain with distension	ND	ND	ND	PRMCN-BM	TR	NED, ND
2	1988	Banerjee⁵	38	F	Left lower abdomen	11	Abdominal pain and distension	ND	Cyst	Cyst with papillary excrescences < 5 mm tall	PRMCN-BM	TR + resection of the descending colon + left salpingo-oopho-rectomy	Media-stinal lymph node meta-stases 4 years after diagnosis
3	1988	Banerjee⁵	47	F	Left upper quadrant mass	13	Flu-like symptoms	ND	ND	Cyst with nodular excrescences measuring up to 3.5 × 2.0 cm	PRMCN-BM	TR + splenectomy+ left adrenal-ectomy	ND
4	1994	Motoyama¹⁷	42	F	Right kidney	6	Symptoms caused by systemic lupus erythematosus	CEA, 98,000 ng/mL	Cyst	Cyst with papillary lesion	PRMCN with foci of mucinous cystadeno-carcinoma	TR	ND
5	1994	Motoyama¹⁷	63	M	Right kidney	11	Abdominal pain	CEA, 15,200 ng/mL	Cyst	Cyst	PRMCN-BM	TR	ND
6	1996	Pearl²⁰	33	F	Retro-peritoneum of the left flank	ND	Increasing abdominal girth, weight gain, and severe back and abdominal pain	ND	Unilocular cyst with homogenous contents	Cyst with several map-like patches	PRMCN-BM	TR	NED, 10 months
7	1997	Papadogiannakis¹⁹	33	F	Lateral to the descend-ing colon	13 × 9	Tiredness, diarrhea and, a feeling of air in the stomach	ND	Cyst with low attenuation	Unilocular cyst with small papillary excrescences measuring 2.0 × 2.0 cm	PRMCN-BM	TR	NED, 12 months
8	1998	Chen⁹	48	F	Mesentery of the ascending colon	15 × 13 × 9	Postprandial fullness	ND	Homogeneous cyst	Cyst	PRMCN-BM	TR	NED, 8 months
9	2003	Gutsu¹²	41	F	Right upper abdominal quadrant	21 × 16	Flank pain and abdominal distension	ND	Mosaic structure	Unilocular cyst with some polypoid masses containing multiple mucin-filled cysts	PRMCN-BM	TR	NED, 18 months
10	2003	Song²¹	31	F	Right retro-peritoneal space	21 × 16 × 10	Abdominal distension	CA 72-4, normal (1.9 /mL)	Multi-septate cyst with calcifications	Multilocular cyst with calcified septa	PRMCN-BM	TR + appendectomy	ND
11	2005	Matsubara¹⁵	36	F	Right lower abdomen	12 × 8	Abdominal distension	CA 125 (51.4 U/mL) and CA 19-9 (55.2 U/mL) were elevated (CEA, normal	Cyst with solid portion	Multilocular cyst with solid mass of 5 cm in diameter	PRMCN-BM	TR + appendectomy+ myomectomy	NED, 6 months
12	2007	Bakker⁴	45	F	Left lower abdomen	15	Abdominal pain	CEA, CA 125, and CA 19-9 were in the normal range	Cyst with nodule	Unilocular cyst with a solid mural nodule of 3.5 × 3.5 × 2.5 cm	PRMCN-BM with a sarcoma-like mural nodule	TR	NED, 12 months
13	2007	Cottrill¹⁰	22	F	ND	20 × 17.5× 15	Abdominal pain and distension	ND	Cyst	ND	PRMCN-BM	TR	NED, ND
14	2008	Bifulco⁷	35	F	Rear of the cecum and near the last intestinal loop	28	Pelvic pain	CA 125, CA 19-9, CA 15-3, tissue polypeptide-specific antigen, and CEA were in the normal range	Cyst with a single septum	Unilocular cyst with a solid area with papillary projections	PRMCN-BM	TR + appendectomy+ partial omentectomy+ multiple biopsies of the peritoneum and ovaries	NED, 24 months
15	2009	Roma³	25	F	ND	15	Kidney mass	ND	ND	Cyst with single papilla	PRMCN-BM	TR	NED, 148 months
16	2009	Roma³	43	F	ND	14	Pelvic pain	ND	ND	Cyst with papilla	PRMCN-BM	TR + SO	NED, 1 month
17	2009	Roma³	35	F	ND	3	Pelvic pain	ND	ND	Multiloculated cyst	PRMCN-BM with microinvasion	TR	NED, 13 months
18	2009	Roma³	48	F	ND	7	Enlarged mass	ND	ND	Thin-walled cyst	PRMCN-BM	TR	NED, 34 months
19	2009	Roma³	47	F	ND	21	Enlarged mass	ND	ND	Cyst with nodules	PRMCN-BM with Ica	TR + SO	NED, 1 month
20	2009	Roma³	24	F	ND	18	Enlarged mass	ND	ND	Thin-walled cyst	PRMCN-BM with ICa	TR	NED, 2 months
21	2009	Roma³	27	F	ND	8	Enlarged mass	ND	ND	Cyst with nodules and papilla	PRMCN-BM with ICa	TR + SO	NED, 11 months
22	2009	Benkirane⁶	44	M	Right side	Four portions of 5 × 4 × 3, 4 × 4 × 3, 3 × 3 × 2, and 2 × 2 × 2	Torsion-like pain and weight loss	ND	Several retroperitoneal masses with heterogenic foci	Multilocular cyst with solid zones	PRMCN-BM	TR	NED, 12 months
23	2011	Falidas¹¹	37	M	Right abdomen	22 × 10	Pain and mass	ND	Cyst with diaphragms	Cysts within the mass, measuring from 1 to 4 cm in diameter	PRMCN-BM	TR	NED, 12 months
24	2013	Mattei¹⁶	32	M	Proximity to the vena cava	6 × 7.1 × 4.4	Incidentally found during work-up for a right testicular mass	ND	Cyst with heterogeneous features	ND	PRMCN-BM	TR	ND
25	2014	Haeri¹³	26	F	Left lower quadrant	13 × 10 × 8	Abdominal distention pain	CEA, AFP, CA 19-9, and CA 125 were in the normal range (3.5 U/mL, 5.3 U/mL, 35.17 U/mL, and 20 U/mL)	Cyst	Cyst with heterogeneous solid and cystic areas	PRMCN-BM	TR	ND
26	2015	Manrai¹⁴	65	F	Left abdominal cavity	20	Abdominal distention	CA 125, normal	Multilocular cyst	Multilocular cyst with small papillary areas	PRMCN-BM	TR	NED, 12 months
27	2015	Vargas²²	68	M	Right abdomen	16 × 4.5 × 11	Palpable mass	CA 19 was slightly elevated; AFP and CEA were in the normal range	Cyst	Multilocular cyst with calcification	PRMCN-BM	TR	ND
28	2019	Chaves⁸	62	F	Right flank	12 × 8.5	Abdominal pain	CEA and CA19-9 were elevated (6.7 ng/mL and 122 U/ mL)	Well-defined hypodense mass with heterogeneous structure	Unilocular cyst	PRMCN-BM	TR + laparoscopic ileocecal resection	NED, 18 months
29	2020	Zhang²³	65	F	ND	ND	Mass	ND	ND	Partially septated cyst	PRMCN-BM	TR	NED, 6 months
30	2020	Zhang²³	23	F	ND	ND	Mass	ND	ND	Unilocular cyst	Mucinous and serous PRMCN-BM	TR	ND
31	2020	Zhang²³	44	F	Left lower quadrant	20	Abdominal distention and a mass	ND	Cyst with mural nodule	Cyst with mural nodules and solid components	PRMCN-BM with Ica	TR	NED, 2 months
32	2022	Present case	39	M	Left pararenal space	6.9 × 4.4	Back pain	AFP and β-HCG were in the normal range	Unilocular homogeneous cyst	Unilocular cyst	PRMCN-BM	TR	NED, 10 months

F, female; ND, not described; PRMCN-BM, primary retroperitoneal mucinous cystic neoplasm with borderline malignancy; TR, tumor resection; NED, no evidence of disease; CEA, carcinoembryonic antigen; PRMCN, primary retroperitoneal mucinous cystic neoplasm; M, male; CA 72-4, carbohydrate antigen 72-4; CA 125, cancer antigen 125; CA 19-9, carbohydrate antigen 19-9; CA 15-3, cancer antigen 15-3; Ica, intraepithelial carcinoma; SO, bilateral salpingo-oophorectomy; AFP, alpha fetoprotein; HCG, human chorionic gonadotropin.

Patients with PRMCN-BM range in age from 22 to 68 years, with a median age of 40 years. The clinical presentation of PRMCN-BM is usually non-specific, with no known specific laboratory tests, tumor markers, or radiological findings. Therefore, the preoperative diagnosis of PRMCN-BM is challenging.²⁵ Serum tumor markers, such as carcinoembryonic antigen, cancer antigen 125, and carbohydrate antigen 19-9, are elevated in a small proportion of these patients, but these elevations do not have diagnostic or prognostic significance. No pathognomonic imaging features of PRMCN-BM have been described to date. These tumors are mainly cystic, with the greatest dimension of the cysts varying from 3 to 28 cm. The cysts may appear unilocular or multilocular, and imaging showed that cysts in only three previously reported cases^11,12^,31 had a solid component or mural nodule. These tumors are localized almost exclusively to the lateral retroperitoneal spaces, with 9 located in the left side and 11 in the right side. The treatment of choice is complete tumor resection, without cyst rupture, thereby preventing tumor cell dissemination.²⁵

The prognosis of patients with these tumors remains uncertain because of their rarity and because most patients were not followed up for ≥ 24 months. Outcomes have been reported in 75% of patients with PRMCN-BM who were followed up for a median of 19 months (range, 1–148 months). Based on published case reports, the overall prognosis of patients with PRMCN-BM and documented disease-free survival was excellent, with little evidence of recurrence, metastasis, or cancer-associated deaths, despite one patient with mediastinal lymph node metastases.⁶ Therefore, tumor resection is curative, with no need for adjuvant chemotherapy. No consensus has been reached on the postoperative follow-up strategy for patients with PRMCN-BM. However, long-term follow-up data are required to better determine the prognosis of patients with PRMCN.

The pathogenesis of PRMCNs has not been determined because epithelial cells are usually absent from the retroperitoneum.^2,10,26 Several hypotheses regarding the origin of these tumors have been proposed. According to one hypothesis, the histological similarity of PRMCNs to ovarian tumors suggests that they arise from ectopic ovarian tissues. However, this hypothesis cannot explain the occurrence of PRMCNs in men or the absence of ovarian tissue from tumors in women. Alternatively, PRMCNs may originate from retroperitoneal monodermal teratomas in which columnar epithelium dominates. In addition, PRMCNs may be remnants of the embryonal urogenital apparatus. The most widely accepted hypothesis is that PRCMNs are derived from invaginated multipotent mesothelial cells that become entrapped in the retroperitoneum during embryonic development, with subsequent mucinous metaplasia and cyst formation. However, in our case, the tumor was not congenital because it was not present on the CT scan performed after surgery (Figure 1).

Targeted next-generation sequencing of tumor DNA in our patient resulted in the identification of two hotspot mutations, with one in KRAS (c.183A>C p. Gln61His) and the other in GNAS (c.602G>A p.Arg201His). No studies to date have determined the molecular profiles of PRMCNs. Therefore, the results in this patient were compared with results in ovarian neoplasms. KRAS mutations have been reported in 30% to 75% of mucinous borderline tumors of the ovaries.²⁷ In contrast, activating mutations of GNAS occur in only a small percentage (2/29, 6.9%) of mucinous borderline tumors of the ovaries, although they are more frequent in other pre-malignant or non-aggressive mucinous-type tumors of gastrointestinal origin.²⁷ The co-occurrence of GNAS and KRAS mutations has been reported in only four mucinous ovarian tumors.²⁷ Additional molecular studies are required to better understand the molecular characteristics of this neoplasm.

Before diagnosing a patient with PRMCN, alternative diagnoses should be excluded by a careful clinical examination, diagnostic imaging, and thorough macroscopic and microscopic evaluations. The differential diagnosis should include metastatic mucinous tumors from the gastrointestinal tract (including the appendix) and the pancreas, which are more common than PRMCN. The possibility of a monodermal variant of a cystic teratoma arising from an undescended testis should also be considered because the retroperitoneum has no epithelial cells.

We describe the rare occurrence of a PRMCN-BM in a male patient. These tumors are rarely included in the differential diagnosis of retroperitoneal masses, and PRMCN-BM is difficult to diagnose preoperatively. The diagnosis of PRMCN-BM involves the exclusion of other considerations, based on careful clinical, imaging, and microscopic evaluations. Surgical excision is the standard approach for the diagnosis and treatment of PRMCN-BM. Evaluation of additional patients is required to better determine the prognosis and optimal postoperative follow-up of this condition.

Footnotes

Author contributions

Seung-Myoung Son made a substantial contribution to writing the manuscript. Chang Gok Woo and Ok-Jun Lee interpreted the pathological data. Seok Jung Yun analyzed the patient’s data. All authors have read and approved the final manuscript.

Declaration of conflicting interest

The authors declare that there is no conflict of interest.

Ethics statement

This study adhered to the guidelines established by the Declaration of Helsinki and was approved by the Institutional Review Board of Chungbuk National University Hospital (Cheongju, Korea, IRB No: 2022-11-013). The patient consented to publication of the case report.

Funding

This research was supported by the Regional Innovation Strategy (RIS) through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (MOE) (2021RIS-001).

ORCID iDs

Seung-Myoung Son

Chang Gok Woo

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