ABCG2 and breast carcinoma: Even though the breast cancer cell lines proved to be more susceptible to 5‐ALA‐PDT, in the case of MCF7 cells, inhibition of ABCG2 or FECH greatly enhanced 5‐ALA‐PDT cytotoxicity, while for MDA‐MB‐231s, ABCG2 inhibition, and intracellular GSH depletion conferred the most profound synergies to 5‐ALA‐PDT.