PNL2: An Adjunctive Biomarker for Renal Angiomyolipomas and PEComas

Abstract

Aims

Renal angiomyolipoma (AML) and perivascular epithelioid cell tumor (PEComa) are members of the microphthalmia-associated transcription factor (MiTF) family of tumors. Traditionally, HMB45 and MelanA have been used to diagnose these lesions; however, low sensitivity can render interpretation difficult. PNL2 is a sensitive and specific biomarker for epithelioid melanoma, and immunoreactivity has also been shown in small series of PEComas. This study determined the utility of PNL2 in MiTF and non-MiTF renal tumors.

Methods and Results

PNL2 immunostaining was performed on 196 tumors, including 40 MiTF renal tumors (AMLs, epithelioid AMLs, sclerosing PEComas, malignant PEComas, and Xp11.2 renal cell carcinomas (RCCs)) and 156 non-MiTF renal tumors. HMB45, MelanA and CathepsinK were also evaluated in a subset of MiTF tumors. Overall, 85% of AMLs and PEComas were positive for PNL2, compared to 81%, 76%, and 95% with HMB45, MelanA, and Cathepsin K, respectively. In 55% of cases, PNL2 stained more extensively when compared to HMB45. PNL2 staining was greater in sclerosing and malignant PEComas (89%) when compared to HMB45 (78%) and MelanA (38%). All remaining renal tumors, except 1 melanocytic Xp11.2 RCC, were negative for PNL2.

Conclusions

NL2 has relatively high sensitivity and specificity for AML and PEComas when compared to non-MiTF renal tumors, and PNL2 appears to be a more useful biomarker for sclerosing and malignant PEComas. For cases that are limited in tissue quantity (i.e., core biopsies) and/or are morphologically suspicious for AML/PEComa, but negative or focally positive for HMB45 and MelanA, PNL2 may be a useful adjunct biomarker.

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