Palbociclib is a cyclin dependent kinase (CDK) 4/6 inhibitor that is indicated in combination with an aromatase inhibitor for first-line treatment of hormone receptor-positive, human epidermal growth factor receptor 2 -negative advanced or metastatic breast cancer. The commonly described side effects of palbociclib are neutropenia, anaemia, thrombocytopenia, fatigue, nausea, stomatitis, alopecia, diarrhoea, decreased appetite, vomiting, asthenia, peripheral neuropathy and epistaxis. However, post approval, increasing use of this drug has revealed another potentially fatal complication, in the form of pneumonitis, especially in the Asian population. The PALOMA 3 trial showed that rates of grade 3 and grade 4 adverse events were modestly higher in Asians than non-Asians, though palbociclib exposure was similar in both races. From this, we could infer that adverse effects of this drug must be monitored more specifically in individual racial populations. We report a patient who developed pneumonitis while on palbociclib and discuss the possible mechanisms and management of CDK 4/6 inhibitor-related lung injury.