ABCG2 and cancer: Combined exposure of the cancer cells to 5‐aminolevulinic acid and Ko143, a specific inhibitor of ATP‐binding cassette transporter G2, further increased protoporphyrin IX‐FI and alleviated the cell‐to‐cell variability in MCF7 and MDA‐MB‐231 cells, indicating improvement in the reproducibility and accuracy for fluorescence‐based cancer detection.