Melanotic Xp11 Translocation Renal Cancer Managed With Radical Nephrectomy and IVC Tumor Thrombectomy

Malignant melanotic Xp11 neoplasms exhibit a clinicopathologic spectrum and gene expression profiling akin to alveolar soft part sarcoma: a proposal for reclassification

The classification of the distinct group of mesenchymal neoplasms, first described as 'Xp11 translocation perivascular epithelioid cell tumor (PEComa)' and for which the term 'melanotic Xp11 neoplasm' or 'Xp11 neoplasm with melanocytic differentiation' has recently been proposed, remains challenging and controversial. We collected 27 melanotic Xp11 neoplasms, the largest series to date, for a comprehensive evaluation. Fourteen of the cases, together with eight alveolar soft part sarcomas (ASPS), nine conventional PEComas and a control group of seven normal tissues were submitted to RNA sequencing. Follow-up available in 22 patients showed 5-year overall survival and 5-year disease-free survival of 47.6 and 35.7%, respectively, which were similar to ASPS and significantly worse than conventional PEComa. Univariate analysis of location (occurring in the kidney versus not kidney), infiltrative growth pattern, nuclear pleomorphism, mitotic activity ≥2/50 high-power fields (HPF), necrosis and lymphovascular invasion were found to be associated with overall survival and/or disease-free survival. Multivariate analysis identified that location was the only factor found to independently correlate with disease-free survival. More importantly, RNA sequencing-based clustering analysis segregated melanotic Xp11 neoplasm and ASPS from other tumors, including conventional PEComa and Xp11 translocation renal cell carcinoma, and formed a compact cluster representative of the largely similar expression signature. Here we clearly define the true biologic nature of melanotic Xp11 neoplasms which are distinctive malignant mesenchymal tumors, rather than simply PEComa variants with occasionally unpredictable behavior. Meanwhile, melanotic Xp11 neoplasm and ASPS more likely represent phenotypic variants of the same entity, which is distinct from conventional PEComa and Xp11 translocation renal cell carcinoma. Based on these important findings, melanotic Xp11 neoplasm might be reclassified into a distinctive entity together with ASPS, independent from PEComa, in future revisions of the current WHO categories of tumors of soft tissue and bone for the improved reclassification. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Melanotic Xp11 translocation renal cancer: a report of a distinctive case and a review of the literature

BACKGROUND

Melanotic Xp11 translocation renal cancer (TRC) is a newly described exceedingly rare tumor, and its characterization remains controversial. This study aimed to describe a case of distinctive melanotic Xp11 TRC and to elucidate its clinicopathological and molecular genetic features.

CASE PRESENTATION

A 44-year-old Chinese female presented with a left renal mass. Abdominal ultrasonography and computed tomography (CT) scans revealed a 4.5 cm × 4.0 cm mass in the left kidney. Grossly, the well-demarcated mass was black with moderately firm consistency. Microscopic examination indicated that the tumor was characterized by the presence of nests and cords of polygonal cells with clear and granular eosinophilic cytoplasm, central round to oval nuclei and occasional nucleoli. Intracytoplasmic melanin was observed in approximately 45% of tumor cells. Uniquely, the tumor presented with intranuclear eosinophilic pseudoinclusions and thick-walled stromal blood vessels. IHC showed that tumor cells were diffusely positive for TFE3 and exhibited patchy and weak HMB45 staining. FISH confirmed the presence of TFE3 rearrangement.

CONCLUSION

This case is the twentieth published case of melanotic Xp11 TRC. Moreover, the present patient had a favorable prognosis given that she was disease free at her 113-month postoperative follow-up. Our case adds to the small body of literature on these exceptionally rare tumors and widens their clinicopathological spectrum.