HPRT1 and B-cell chronic lymphocytic leukemia: In current study, we used three housekeeping genes, namely, YWHAZ, UBC, and HPRT1, that have been shown to be optimal for PCR data normalization in different types of lymphoid tissue 18, Regarding ZAP70 expression, the B‐CLL samples in our dataset can be divided into the following two groups (Table 2): low ZAP70 mRNA expression (8 samples, normalized cDNA quantity lower than 0.04, median 0.01) and high ZAP70 mRNA expression (12 samples, normalized cDNA quantity higher than 0.15, median 0.31).