ERBB2 and breast cancer: For example, long-term exposure to HER2-targeting ADC, the breast cancer cell lines will reduce the expression of HER2 receptors and reduce lysosomal acidification to slow down protein degradation and metabolism.266 Some ATP-binding cassette (ABC) transporters have been found to be important in the export anticancer drugs and render tumors resistant.267 The common payloads used in ADC, like MMAE, MMAF and calicheamicin, can be exported outside cancer cells by ABC transporters, which makes these ADCs show drug resistance.268