 The Phase 2 part of the study will be a dose expansion study and will be open to 2 groups of participants. Those with progressive NF-1 related optic pathway gliomas OPG, and those with NF1 related inoperable PN. This part of the study will only commence when the recommended phase 2 dose is established from part 1. The purpose of this part of the study is to determine the effectiveness of the 5 out of 7 day intermittent dosing schedule of Selumetinib, using response rates and duration of response, appropriate MRI criteria and functional assessments REINs criteria. The investigators plan to further evaluate the acute and chronic toxicities of selumetinib in this population and to assess the clinical status and quality of life in this population. 