Benign metastasizing leiomyoma with retroperitoneal lymph node involvement in a patient with a history of renal cell carcinoma.

A 44-year-old Hispanic female was referred after an incidental mass found on her left kidney, which began increasing in size. The patient was status post transvaginal hysterectomy for endometriosis 1-year prior, and her past medical history was significant for inflammatory polyarthritis, hypertension, congenital von Willebrand disease type 1, subclinical hypothyroidism, and depression. She was a former smoker, and her family history was negative for genitourinary issues. Physical examination, including the genitourinary system, was unremarkable. The patient underwent an uneventful robotic left partial nephrectomy, after which pathological examination revealed stage pT1aNx clear cell RCC with negative surgical margins. The patient was followed regularly, according to the guidelines, with imaging and labs and remained cancer-free. Nevertheless, computed tomography (CT) at an 18-month follow-up demonstrated two enlarged retroperitoneal lymph nodes, measuring 12 mm × 12 mm and 10 mm × 9 mm, as well as bilateral pelvic lymphadenopathy [ Figure 1 a and b]. Given the uncertainty of the lymph nodes origin, a percutaneous CT-guided biopsy was performed from the left external iliac lymph nodes. Pathologic assessment revealed a cellular spindle cell tumor with smooth muscle cell differentiation and mild atypia. On immunohistochemistry staining, the tumor cells were positive for smooth muscle actin, desmin, estrogen receptor (ER), progesterone receptor (PR), Wilms tumor protein 1, and cathepsin K. The tumor was negative for HMB45, Melan A, myogenin, MyoD1, anaplastic lymphoma kinase 1, EBERISH, CD117, DOG1, AE1/AE3, and S100. Fumarate hydratase immunostain performed at an outside facility was found to be retained. MDM2 FISH was also negative [ Figure 2 ]. The patient underwent robotic extended pelvic lymph node dissections. The final pathology revealed a smooth muscle cell tumor consistent with a BML in 5 of 29 lymph nodes. Enlarged (a) left retroperitoneal and (b) bilateral pelvic lymph nodes before surgery (white arrows show the location of lymph nodes). Computed tomography images 1 year following surgery showing no lymph nodes in the (c) retroperitoneum and (d) pelvis, with postoperative changes Pathology slides depicting (a) Hematoxylin and Eosin image of benign metastasizing leiomyoma (BML) within a lymph node appearing to extend into the adjacent fibroadipose tissue, (b) Immunostain desmin shown to highlight the BML as a tumor of smooth muscle differentiation. The magnification is 200x After a multidisciplinary tumor board discussion, she underwent robotic retroperitoneal lymph node dissection 3 months later. Pathology revealed similar findings in 8 out of 17 lymph nodes. Postoperative courses of both surgeries were uneventful with no perioperative complications. The patient was followed for 3 years and remained asymptomatic with unremarkable imaging [ Figure 1 c and d] and laboratories.

Benign metastasizing leiomyoma (BML) is a benign growth of extra-uterine smooth muscle cells.[ 1 2 ] Despite their metastatic behavior, BMLs are defined by benign histological features, including low mitotic activity, absence of nuclear pleomorphism, and no evidence of invasion. They are often found in the lungs of women who have previously undergone uterine surgery.[ 1 2 ] The exact etiology of these tumors is not yet known; however, they are thought to arise from either coelomic metaplasia of mesenchymal tissue or peritoneal seeding of uterine fibroid tissue.[ 1 ] Nonetheless, data is limited to case studies and small series, given the scarcity of documented cases. Patients with a history of malignancy and de novo adenopathy remain under high suspicion of malignant metastasis and investigating the origin of new tumors is a high priority. Herein, we present a case of a patient with BML identified in the retroperitoneum in the setting of renal cell carcinoma (RCC). This case study was compiled in concordance with The Surgical CAse REport guidelines. The patient gave informed consent for her clinical information to be used in a journal article.

A comprehensive evaluation of new adenopathy following urological oncologic surgery is important to rule out the possible presence of metastasis. Although rare, BML should be considered among the differential diagnoses among female patients with a history of uterine pathologies. Once a diagnosis is made, patients should be educated on their prognosis with BML and closely monitored including surveillance imaging. 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. There are no conflicts of interest.

BML is a rare disease, with approximately 150 cases reported.[ 3 ] This is the first case study to describe BML in the context of renal malignancy. BMLs are rather rare and can be completely asymptomatic, which makes the exact incidence difficult to estimate. Premenopausal women who have undergone uterine surgery are the primary group affected by BML, as was the case in our patient with a prior hysterectomy.[ 1 2 ] BML originates from uterine leiomyoma tissue that migrates most commonly to the lungs and lymph nodes, though other soft tissues and bone may be involved.[ 1 2 ] The prognosis of BML is good as these tumors grow slowly and are often identified months to more than 30 years after uterine surgery. Frequently mistaken for malignancies, series describing BML with concurrent malignancy are sparse. Our patient underwent a biopsy to confirm the etiology of the retroperitoneal adenopathy. In the setting of RCC, a particularly aggressive neoplasm, confirming metastasis or lack thereof is critical.[ 4 ] Ruling out metastasis in our patient was the impetus for performing a biopsy on her retroperitoneal lesions; however, BML may be a diagnosis of exclusion, given the rarity.[ 1 2 ] Our patient did not have the typical presentation of a BML. She did not report a history of uterine fibroids, though she did undergo hysterectomy. Given that 20%–30% of women over 35 years old experience uterine leiomyoma, it is possible that she was unaware of the presence of a fibroid, either intra- or extrauterine.[ 5 ] In addition, the time between the initial surgery and the diagnosis of BML is typically estimated to range from 10 to 15 years. In contrast, in our patient’s case, this interval was notably shorter at just 3 years. The significance of this patient’s endometriosis in the setting of a BML is yet to be determined; however, endometriosis has also been reported to seed beyond the pelvis.[ 5 ] Endometriosis was not the etiology of our patient’s adenopathy, as BML was histologically confirmed. Standardized management of BMLs has not yet been described. However, the slow-growing nature of the benign tumors calls for conservative, frequent monitoring after other malignancies have been excluded. At present, no treatment exists specifically for BML. Nevertheless, in patients who are experiencing significant pulmonary symptoms, resection of uterine fibroids and hormonal management may be considered.[ 2 ] Progestin and estrogen have been associated with the growth of BML lung nodules; therefore, gonadotropin-releasing hormone analogs, selective ER modulators, selective PR modulators, and aromatase inhibitors may be indicated. Bilateral or unilateral oophorectomy may also be considered in cases of lung involvement.[ 2 ]