Rad6–Rad18 complex responsible for PCNA ubiquitination is important, but not essential for TLS.335 Overexpression of Rad6 ubiquitin conjugating enzyme is correlated with cisplatin resistance in triple-negative breast cancer.336 Therefore, Rad6–Rad18 system may provide another possible target for chemotherapeutic intervention. Here, RAD18 is linked to triple-negative breast carcinoma.