Primary Ewing Sarcoma of the Mastoid: A Novel Case Mimicking Acute Mastoiditis.

Ewing sarcoma (EWS) is a primitive neuroectodermal tumor arising in bone or soft tissue. It is the second most common primary bone malignancy of children and adolescents, with a peak incidence in the second decade of life. It most often arises in the long bones of the extremities and pelvis. Here, we present a novel case of EWS arising from the mastoid bone in a 5-year-old African American male who presented with symptoms of acute mastoiditis. This unique presentation highlights the importance of considering EWS in a patient who presents with atypical mastoiditis or a rapidly growing mass in the postauricular region.

MAPK signaling cascades mediate distinct glucocorticoid resistance mechanisms in pediatric leukemia.

The outcome for pediatric acute lymphoblastic leukemia (ALL) patients who relapse is dismal. A hallmark of relapsed disease is acquired resistance to multiple chemotherapeutic agents, particularly glucocorticoids. In this study, we performed a genome-scale short hairpin RNA screen to identify mediators of prednisolone sensitivity in ALL cell lines. The incorporation of these data with an integrated analysis of relapse-specific genetic and epigenetic changes allowed us to identify the mitogen-activated protein kinase (MAPK) pathway as a mediator of prednisolone resistance in pediatric ALL. We show that knockdown of the specific MAPK pathway members MEK2 and MEK4 increased sensitivity to prednisolone through distinct mechanisms. MEK4 knockdown increased sensitivity specifically to prednisolone by increasing the levels of the glucocorticoid receptor. MEK2 knockdown increased sensitivity to all chemotherapy agents tested by increasing the levels of p53. Furthermore, we demonstrate that inhibition of MEK1/2 with trametinib increased sensitivity of ALL cells and primary samples to chemotherapy in vitro and in vivo. To confirm a role for MAPK signaling in patients with relapsed ALL, we measured the activation of the MEK1/2 target ERK in matched diagnosis-relapse primary samples and observed increased phosphorylated ERK levels at relapse. Furthermore, relapse samples have an enhanced response to MEK inhibition compared to matched diagnosis samples in xenograft models. Together, our data indicate that inhibition of the MAPK pathway increases chemosensitivity to glucocorticoids and possibly other agents and that the MAPK pathway is an attractive target for prevention and/or treatment of relapsed disease.