Rare tumors are understudied, yet have the potential to shed light on vast areas of cancer research. Ovarian sex cord-stromal tumors, rare tumors of childhood and young adulthood, have recently been found to be associated with a lung cancer of early childhood called pleuropulmonary blastoma (PPB). The cause of these ovarian tumors is unknown. DICER1 mutations are seen in the majority of children with PPB. Research shows DICER1 mutations are also seen in some patients with ovarian tumors. Like PPB, ovarian stromal tumors are highly curable when found in early stage; however, later forms of the disease are aggressive and often fatal. The International Ovarian Stromal Tumor Registry collects clinical and biologic data to understand why these tumors occur and how to treat them. Current work involves the study of the role of DICER1 and miRNA expression in ovarian stromal tumors. Understanding the clinical history, predisposing factors and DICER1 and miRNA expression in these ovarian tumors of childhood will lead to targeted screening and risk stratification for evidence-based treatment and biologically rational therapies. These efforts will improve the lives of children by increasing survival and reducing late effects.