Primary retroperitoneal mucinous cystic neoplasm of borderline malignancy with KRAS and GNAS - co-mutation: a case report

Sep 24, 2026

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Primary retroperitoneal mucinous cystic neoplasms are rare retroperitoneal tumors histologically resembling ovarian mucinous cystic neoplasms. Only 31 cases of primary retroperitoneal mucinous cystic neoplasm with borderline malignancy (PRMCN-BM) have been reported, including 26 women and five men. The report adds a male patient: a 39-year-old man with back pain whose lesion was excised laparoscopically and showed atypical mucinous intestinal epithelium. Targeted sequencing identified KRAS and GNAS hotspot mutations, and follow-up showed no recurrence.

LanguageEnglish

CategoryHealthcare

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Reading Time25 min

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Abstract

Introduction

Case report

Presentation and prior history

Imaging and preoperative assessment

Surgical management and pathology

Primary retroperitoneal mucinous cystic neoplasm of borderline malignancy with KRAS and GNAS co-mutation: a case report Seung-Myoung Son 1 , Chang Gok Woo 1 , Seok Jung Yun2 and Ok-Jun Lee 1 Journal of International Medical Research 2023, Vol. 51(5) 1–10! The Author(s) 2023 Article reuse guidelines: [sagepub.com/journals-permissions](sagepub.com/journals-permissions)[ ](sagepub.com/journals-permissions)[DOI: 10.1177/03000605231172469](DOI: 10.1177/03000605231172469)[ ](DOI: 10.1177/03000605231172469)[journals.sagepub.com/home/imr](journals.sagepub.com/home/imr) 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 PRMCNBM. 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. 1 Department of Pathology, Chungbuk National University Hospital, Chungbuk National University College of Medicine, Cheongju, Republic of Korea 2Department of Urology, Chungbuk National University Hospital, Chungbuk National University College of Medicine, Cheongju, Republic of Korea Corresponding author: Ok-Jun Lee, Department of Pathology, Chungbuk National University Hospital, Chungbuk National University College of Medicine, 1 Chungdae-ro, Seowon-gu, Cheongju 28644, Republic of Korea. [Email: md5218@naver.com](Email: md5218@naver.com) Creative Commons Non Commercial CC BY-NC: This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 License ([https://creativecommons.org/licenses/by-nc/4.0/](https://creativecommons.org/licenses/by-nc/4.0/)) which permits non-commercial use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages ([https://us.sagepub.com/en-us/nam/open-access-at-sage](https://us.sagepub.com/en-us/nam/open-access-at-sage)). Keywords Primary retroperitoneal mucinous cystic neoplasm, borderline malignancy, retroperitoneum, case report, KRAS, GNAS Date received: 02 December 2022; accepted: 11 April 2023 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 patho

FAQs

What condition does the case report focus on?

The article focuses on primary retroperitoneal mucinous cystic neoplasm with borderline malignancy (PRMCN-BM), described in an additional male patient.

What did imaging show before surgery?

Computed tomography revealed a 6.9 × 4.4 cm cystic mass in the left pararenal space without mural nodules and without findings such as peritoneal implants, ascites, or lymphadenopathy.

Which gene mutations were identified, and what was the follow-up outcome?

Targeted next-generation sequencing identified hotspot mutations in both KRAS and GNAS. Outpatient follow-up 10 months after surgery showed no evidence of tumor recurrence.

Sep 24, 2026

Uploaded by Riley