A reverse transcription polymerase chain reaction (RT-PCR)–based 3-gene PI is a biomarker of therapeutic response in AML (SAL series). (A) Detection of CALCRL, LSP1, and CD109 mRNA by quantitative RT-PCR in leukemia cell lines. Bars denote mean ± standard error of the mean (duplicate measurements). (B) Detection of CALCRL, LSP1, and CD109 mRNA by RT-PCR in BM samples from the SAL series (38 adults with newly diagnosed AML; clinical characteristics in supplemental Table 6). The PI was calculated as detailed in “Materials and methods.” (C) Detection of CALCRL, LSP1, and CD109 protein by western blotting (supplemental Materials and methods) in 23 BM samples from the SAL series. (D) Correlation between PI category (median split) and response to induction chemotherapy in the SAL series. Early blast clearance, a major independent predictor of therapy response and long-term outcomes, was defined as having <10% leukemia blasts on day 16 (1 week after the end of the first cycle of induction chemotherapy), as previously described.³⁵  (E) CALCRL, LSP1, and CD109 mRNA levels (duplicate measurements) in matched BM samples from 9 patients in the SAL series who later developed leukemia relapse. The analysis of variance test for paired determinations was used for statistical comparisons between gene expression at diagnosis and time of relapse.