MKI67 and cancer: This is congruent with previous guidelines: In 2016, ASCO released clinical practice guidelines, which distinctly outlined that the ‘Protein encoded by the MKI67 gene labelling index by immunohistochemistry should not be used to guide choice on adjuvant chemotherapy’, and hesitancy in relying upon ‘Ki-67 protein levels in tumour cells to make recommendations about the type of hormonal therapy prescribed after surgery’, as well as ‘cancer cells with high levels of Ki-67 don’t respond well to aromatase inhibitors’ [22].