Pediatric Renal Tumors: Updates in the Molecular Era

Recent Advances in Renal Medullary Carcinoma

Renal medullary carcinoma (RMC) is a rare renal malignancy that has been associated with sickle hemoglobinopathies. RMC is aggressive, difficult to treat, and occurs primarily in adolescents and young adults of African ancestry. This cancer is driven by the loss of SMARCB1, a tumor suppressor seen in a number of primarily rare childhood cancers (e.g., rhabdoid tumor of the kidney and atypical teratoid rhabdoid tumor). Treatment options remain limited due in part to the limited knowledge of RMC biology. However, significant advances have been made in unraveling the biology of RMC, from genomics to therapeutic targets, over the past 5 years. In this review, we will present these advances and discuss what new questions exist in the field.

Commentary on: SMARCB1 as a novel diagnostic and prognostic biomarker for osteosarcoma

In the last couple of decades, biomarkers have been on the rise for diagnostic and predictive value. There has been a rush to identify new markers using new technologies and drug repurposing approaches. SMARCB1 acronym arises from the SWI/SNF (SWItch/Sucrose Non-Fermentable)-related Matrix-associated Actin-dependent Regulator of Chromatin subfamily B member 1 (SMARCB1). It is a molecule, whose role is associated with the sucrose metabolism. SMARCB1 is also called INI1 (Integrase Interactor 1). The molecule was discovered in the mid-1990s. Its role as a loss-of-function marker for malignant rhabdoid tumors (MRT) of renal and extrarenal origin has enormously expanded the spectrum of involved neoplasms since that time. Several tumors have been characterized by genetic aberrations in the SMARCB1 gene. They include reduction in expression, loss of expression, and mosaic expression. Most of the tumors are sarcomas, but a variegated group of tumors with mixed phenotypes has also been delineated. It is well known that the outcome of patients harboring genetic aberrations in the SMARCB1 gene has been poor. Guo et al. reported that reduced SMARCB1 expression occurred in 70% of osteosarcomas. Their data significantly correlated with poor neoadjuvant response. These authors emphasize a shorter progression-free and overall survival of the patients demonstrating an altered expression of this gene. Interestingly, mRNA in silico analysis established that SMARCB1 expression correlates with the response to chemotherapy of osteosarcoma patients, but there was no reliable correlation between SMARCB1 expression level and metastasis, response to neoadjuvant therapy, overall survival, and progression-free survival. The study involved a tissue microarray (TMA) on bone tumors that may limit the full evaluation of the gene expression. Nevertheless, Guo et al.’s study is remarkable. It expands the list of the tumors harboring an altered SMARCB1 gene expression and suggests that this marker should be investigated in every pathology workup for potential predictive value. On the other side, much work needs to be done if we hope that we strive to provide additional therapeutic strategies for osteosarcoma patients with altered SMARCB1 gene expression.

Anaplastic Sarcoma of the Kidney With Heterologous Ganglioneuroblastic Differentiation: Another DICER1-Associated Tumor

Anaplastic sarcoma of the kidney (ASK) is a rare renal tumor for which less than thirty cases have been described in the literature to date. Diagnosis of ASK is primarily based on histology, which features solid spindle cell neoplastic islands arranged in a fascicular pattern, prominent anaplastic nuclear morphology, brisk mitoses, and multiple multiloculated cysts lined by hobnail epithelium reminiscent of cystic nephroma. Chondroid or rhabdomyocytic differentiation is often present within the sarcoma. It has been recently suggested that this tumor entity belongs to the DICER1 syndrome tumors based on identification of DICER1 mutations. We report on a case of this rare tumor found in a twenty-month-old female. In addition to the typical histologic findings of ASK, this case also displayed heterologous neuroblastic-gangliocytic differentiation, which has not been previously described in the literature. TP53 and BRAF v600E had aberrant immunostaining. Chromosomal microarray and genomic sequencing revealed loss of chromosome 10 p15.3-p11.2 and both somatic and germline DICER1 mutations, consistent with recent research and further supporting the classification of this tumor within the DICER1 syndrome associated tumors.