CHEK1 and neoplasm: In another study, it was shown that olaparib, after 5 days of treatment in the 0.1–1 μM range of concentration, was more cytotoxic in BRCAMUT cells (PEO-1, JHOS4) compared with HR-proficient cells (PEO4REV, WO-20 ATR/CHK1 primary tumor cultures, BRCAWT).