HK2 and breast cancer: Experimental studies have shown that the composition ratio of PK subtypes in a variety of drug-resistant cell lines cultured in vitro has changed.[38] Expression of HK-II in 5-fluoruracil-resistant gastric cancer cells (AGS) is upregulated.[39] The expression of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) is upregulated in paclitaxel-resistant breast cancer cells (MCF-7).[40]