RAD1 and mantle cell lymphoma: In contrast to the observations by Zhang et al., the differences in OCR/ECAR ratios between ibrutinib-sensitive and resistant MCL cell lines were not confirmed by our results, showing similar ratios for ibrutinib-sensitive REC-1 and resistant MAVER-1, which may be due to different culture conditions, cell density, and experimental setup in general [19, 46, 47].