 Akaita mutambo wake wekutanga mumakwikwi epasi rose mumakwikwi emamita mazana masere pamakwikwi eAfrican Championships muAthletics muna 2010muNairobi, asi akakundikana kupinda mumakwikwi okupedzisira. Muna 2011, Sum akaisa nguva yake yakanakisisa ye1:59.66 pakupedza wechipiri pamusoro pe800 m pamakwikwi eKenya. Kuita uku kwakaita kuti Sum akwanise kumhanya mamita 800 pa2011 World Championships in Athletics muDaegu, South Korea, kwaakasvika kuma semi finals. 