Mesothelioma of Uncertain Malignant Potential (MUMP) of the Tunica Vaginalis: Proposal for Reclassification as "Complex Mesothelial Tumor of the Tunica Vaginalis".

A well-differentiated papillary mesothelial tumor (WDPMT) and malignant mesothelioma are 2 well-recognized entities arising from the testis tunica vaginalis. Another mesothelial lesion exclusively seen at this site is mesothelioma of uncertain malignant potential (MUMP)-a lesion reminiscent of WDPMT yet demonstrating variable proportions of more complex architectural patterns that could be confused with invasion. MUMP was first described in 2010 with a total of 11 cases reported to date. Herein, we describe 19 additional patients who underwent hydrocelectomy, excision, and/or orchiectomy. Novel morphologic patterns found in addition to the 2010 series include spindle cells, keloidal-type collagen, and multicystic architecture lined by bland mesothelial cells. Clinical follow-up in 9 patients for more than 1 year (1.5 to 22.5 y, median 4.5 y) revealed no evidence of disease recurrence or metastases. Despite greater architectural complexity, MUMP has (1) bland cytology; (2) merging in with WDPMT areas; (3) low mitotic rate and Ki-67 nuclear labeling index; (4) retention of MTAP and BAP1 expression; and (5) benign clinical follow-up. If these cases were malignant mesotheliomas, one would have expected at least some of the patients to demonstrate disease recurrence/progression without adjuvant therapy within the available follow-up time, particularly with limited resection in most patients. Thus, we propose that "mesothelioma of uncertain malignant potential" be renamed as "complex mesothelial tumor of the tunica vaginalis." Using the term "complex" draws a contrast with the simple cuboidal lining and simple papillary architecture seen in WDPMT. Also, labeling the lesion as "tumor" removes the stigmata of "uncertain malignant potential" and "mesothelioma" that are alarming to patients and clinicians, and potentially could unduly lead to more extensive surgery in an attempt at "complete" resection. At the same time, not definitively labeling the lesion as benign allows recommendations for follow-up.

Comparative Analysis of Surgery, Thermal Ablation, and Active Surveillance for Renal Oncocytic Neoplasms.

OBJECTIVE: To compare oncological and procedural outcomes for renal oncocytic tumors treated with surgery, thermal ablation, or active surveillance. METHODS: Clinical and pathologic data were collected for consecutive patients with a histologic diagnosis of oncocytoma, oncocytic neoplasm, or chromophobe renal cell cancer (chRCC) from 2003 to 2016. Independent pathology and radiology reviews were performed for this study. RESULTS: Of 171 patients, tumor histology included oncocytoma (n = 122), chRCC (n = 47), and oncocytic neoplasm not otherwise specified (n = 2). At the initial diagnosis, 67, 14, and 90 patients were treated with surgery, thermal ablation, and active surveillance. In 3 of 19 patients (16%) who had biopsy and subsequent surgery, diagnosis changed from oncocytoma to chRCC. The median follow-up was 39.9 months with no difference among choices of treatment modalities (P = .33). Of 90 patients who began active surveillance, 32 (36%) switched to active treatments (19 underwent thermal ablation and 13 underwent surgery). The median linear growth rate for patients on active surveillance was 1.2 mm/y. No patients who were managed with active surveillance developed metastatic renal cell cancer (mRCC). mRCC was identified in 3 patients and was the cause of death in 2 patients. Patients who developed metastatic disease presented with symptomatic tumors of >4 cm and were treated with immediate surgery. For oncocytic masses of ≤4 cm (n = 126), the 5-year cancer-specific survival was 100%. CONCLUSION: Renal oncocytic neoplasms have favorable oncological outcomes. Active surveillance is safe and is the preferred management for small (≤4 cm) oncocytic renal tumors in selected patients.