Expression of WT1 in renal rhabdoid tumors: immunohistochemistry and molecular genetics

Renal rhabdoid tumor (RRT) is the most malignant and aggressive renal tumors in children. The results of immunohistochemistry show co-expression of epithelial and mesenchymal markers with total loss of INI1 expression in tumor cells. Aim. To determine the frequency of WT1 expression in RRT using three different clones and to investigate WT1 gene status. This study is supported by the Independent Ethics Committee and approved by the Academic Council of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology. 28 patients with RRT were included in our study from a period 2006–2019. Immunohistochemical staining included Vimentin, panCK, CK19, EMA, INI1, CD34, WT1 (clones: polyclonal, WT49, 6FH2). Additionally, in order to evaluate genetic events known to be significant in the RRT pathogenesis, molecular genetic testing by multiplex ligase-dependent probe amplification (NGS) and next-generation sequencing (NGS) of customized gene panel were conducted in 15 cases with available material. All tumors had classical rhabdoid morphology with co-expression of epithelial and mesenchymal markers and total loss of INI1 expression. Two tumors were WT1-positive (WT49 and Polyclonal). 5 out of 15 tumors harbored different in length SMARCB1 gene deletions. 7 cases studied by NGS for nucleotide substitutions and small indels included 5 patients lacking SMARCB1 deletions based on the MLPA data and 2 cases of RRT with WT1 protein nuclear expression. All evaluated patients had pathogenic or likely-pathogenic genetic variants in genes encoding core subunits of SWI/ SNF chromatin remodeling complex (predominantly, SMARCB1 and SMARCA4 genes). No pathogenic variants were revealed in WT1 gene. The literature describes isolated cases of WT1 expression in RRT elements. Often, the cellular elements of a rhabdoid tumor after preoperative chemotherapy are regarded as elements of the stromal component of nephroblastoma, maturing into rhabdomyoblasts. In the presence of WT1 expression, these tumors are considered as nephroblastomas. In this study we showed that RRTs are molecularly heterogeneous tumors with aberrant immunophenotype. Thus, our experience proves the importance of an integrated approach to differential diagnosis and the need for routine use of the INI1 antibody in panels for the study of kidney tumors in children to avoid misinterpretation of morphological data.

The Genomic Landscape of Wilms' Tumor 1 (WT1) Mutant Acute Myeloid Leukemia

Mutations in tumor suppressor genes and oncogenes are both potentially therapeutically actionable in acute myeloid leukemia (AML). The Wilms' Tumor 1 (WT1) gene is located on 11p13 and encodes a zinc finger transcription factor which has been found to be overexpressed and mutated in AML. In normal development, WT1 is only expressed in a small subset of hematopoietic stem cells. While its overexpression suggests an oncogenic role, the invariable presence of mutations in the cysteine-histidine zinc finger domains indicates a tumor suppressor function, similar to that in WAGR syndrome/11p deletion syndrome in which it was first discovered. Like its unknown function in AML, the clinical significance and genetic associations of WT1 mutations have been also controversial. Although studies of WT1 mutations in AML have been conducted, the lack of solid clinical and molecular characterization of large WT1-mutant (WT1MT) AML cohort has hampered its definition. In this study, we took advantage of a compendia of genomic results from Cleveland Clinic and publicly available data of 2188 AML patients (primary (p)AML, n= 1636; secondary (s)AML, n= 433; therapy-related (t)AML, n= 119, excluding cases with acute promyelocytic leukemia, MLL-rearrangement, and core-binding factor AML). While several reports only focused on cytogenetic normal AML (CN-AML), which represented 61% of our cohort, we additionally included all other cytogenetic risk groups. In total, WT1 mutations were detected in 5% (114/2188) of patients. WT1 mutations were enriched in pAML (85%) compared to sAML (11%) and tAML (4%). Thirty-nine patients (13%) carried more than 1 WT1 mutation. WT1MT were younger [59 vs 64 years, P=0.0002] and more often females (55% vs 45%, P=0.03) as compared to WT1 wild type (WT1WT) patients. Univariate analyses of baseline parameters showed that WT1MT AML had a more proliferative phenotype with a higher WBC [15.1 vs 9.5 x109/L, P=0.03] and bone marrow blast percentages [73 vs 59%, P=0.002] and with lower platelet counts [44 vs 56 x109/L, P=0.008] compared to WT1WT cases. In the WT1MT cohort, 70% had a normal karyotype, with complex karyotype being significantly less frequent vsWT1WT patients [4 vs 16%, P=0.001]. The most common cytogenetic abnormalities in WT1MT patients included +8 (8%) followed by -9/del(9q) (3%) and -7/del(7q) (3%). Only 1 patient carried inv(3)/t(3;3) or -17/del(17p). In sum, no statistical differences in cytogenetics were found between WT1MTvsWT1WT AML patients. Next, identified mutational signatures of WT1MT patients. A panel of 44 myeloid genes and their hotspot configurations were selected according to their relevance in AML. In comparison to WT1WT AML patients, multivariate analyses showed that WT1MT patients had higher odds of biallelic CEBPA (12 vs 3%; P=0.009) and FLT3 internal tandem duplication mutations (FLT3ITD, 31 vs 16%; P=0.01) but lower odds of SRSF2 mutations (2 vs 9%, P=0.04). Since FLT3ITD has been previously described to be associated with WT1 mutations, we also focused on investigating whether mutations in the tyrosine kinase domain (TKD) were frequent in WT1MT as well. Although we found increased percentages of FLT3TKD (11%) among the WT1MT patients compared to WT1WT cohort (8%), this difference did not reach statistical significance. To uncover multifactor lesions (cytogenetic and/ or additional molecular lesions) of prognostic importance, we performed survival analyses. Although the combination of WT1 mutations and FLT3TKD shortened overall survival (OS) by 2-times in WT1MT patients vsWT1WT cases with FLT3TKD (23.7 vs 45.9 months), this result was not significant (P=0.1). In addition, the concurrent presence of other cytogenetic and molecular features didn't reveal significant impact on OS. In sum, using an adequately powered cohort, our study of the genomic landscape of WT1MT AML patients identified its genomic associations and their clinical and prognostic inferences. The application of advanced machine learning methods to large datasets of WT1MT AML patients might be crucial to capture the complex genomic interactions of WT1 gene in AML. Disclosures Carraway: BMS: Consultancy, Other: Research support, Speakers Bureau; Stemline: Consultancy, Speakers Bureau; Takeda: Other: Independent Advisory Committe (IRC); ASTEX: Other: Independent Advisory Committe (IRC); Abbvie: Other: Independent Advisory Committe (IRC); Novartis: Consultancy, Speakers Bureau; Jazz: Consultancy, Speakers Bureau. Nazha:MEI: Other: Data monitoring Committee; Novartis: Speakers Bureau; Incyte: Speakers Bureau; Jazz: Research Funding. Sekeres:Pfizer: Consultancy; BMS: Consultancy; Takeda/Millenium: Consultancy. Maciejewski:Alexion, BMS: Speakers Bureau; Novartis, Roche: Consultancy, Honoraria.