ERBB2 and breast carcinoma: The authors hypothesised that photooxidative damage to HER2 with the light‐before treatment resulted in less efficient drug delivery.28 Gelonin was similarly targeted against several breast cancer cell lines showing different levels of expression of HER‐2 receptor,33 and it was shown that in addition to toxin uptake, relative cellular sensitivity to the toxin is also an important factor affecting PCI efficacy.33