Published in the Red Journal, this systematic review included 32 studies (1452 early breast cancer patients) treated with adjuvant PBT. Scattering PBT was delivered in seven studies (258 patients) and scanning PBT in 22 studies (1041 patients). The synthesis of this data showed that adverse events were less severe after scanning than after scattering PBT. For partial breast PBT, severe dermatitis after scattering PBT was 4% (7/169) and 0% after scanning PBT (0/114). For whole breast or chest wall +/- regional lymph nodes PBT, 4% (44/1026) of events were severe after scanning PBT. The most prevalent severe outcome after scanning PBT was dermatitis which occurred in 5.7% of patients. Other severe adverse outcomes included infection, pain and pneumonitis (each ≤1%). Of the 141 reconstruction events reported, the most prevalent after scanning PBT was prosthetic implant removal (34/181, 19%). 19 locoregional recurrences were reported from 867 patients in 19 studies, 53 distant recurrences were reported from 811 patients in 16 studies. Few studies reported outcomes beyond three years, and there is no randomized study comparing PBT with photons. Ongoing randomized clinical trials are likely to provide comparative data on the longer-term safety and effectiveness of PBT.