SERPINE2 and medulloblastoma: We show that siRNA-mediated lowering of SERPINE2/PN-1 in human medulloblastoma DAOY cells or genetically in Ptch1Δ/+Pn-1Δ/+ mice reduces cell proliferation and results in the majority, but not all PNLs remaining as small cerebellar nodules rather than progression to malignant medulloblastomas.