Sakari studied medicine at the University of Helsinki, Finland, where he attended the MD/PhD program. He completed his PhD work on human tumor genetics under the supervision of Lauri A. Aaltonen. After graduation he spent some time in clinical training before joining the laboratory of Joan Massagué at the Memorial Sloan Kettering Cancer Center, New York, where he worked on the molecular mechanisms of metastatic cancer progression. In 2014 Sakari joined the MRC Cancer Unit at the University of Cambridge as an independent group leader, with promotion to program leader in 2019. In 2022 he relocated to the Translational Cancer Medicine Program at the University of Helsinki. He was recently awarded the Sigrid Jusélius Professorship in basic medicine.