The Run 2 of the LHC opened up the possibility to measure various large-mass elementary particles for the first time in heavy ion collisions, in particular the top quark. The top quark is a novel tool for probing the nuclear parton distribution functions, the mechanisms of parton energy loss, and the medium opacity at different space-time scales. Using pPb and PbPb data, the CMS experiment measured for the first time top quark production in heavy ion collisions. In the talk, a review of these measurements and the acompannying pp reference ones, is given. The focus is put on the recent first observation of top quark pair in PbPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV, using an integrated luminosity of about 1.7/nb