Elevated ss-MSLN in patients with MSLN⁺AML. (A) ss-MSLN levels at diagnosis in 337 pediatric patients and 43 adult AML patients, measured by ELISA, comparable to Mesomark. Using a positivity threshold ≥1.5 nM, 25% of pediatric patients and 33% of adult AML patients were positive for soluble MSLN. (B) ss-MSLN levels correlate with MSLN transcript levels detected by RNA-Seq (Spearman r = +0.57; P < .0001). Thresholds of MSLN⁺ ≥1.5 nM and ≥5 TPM are illustrated. (C) ss-MSLN levels in 39 AML patients who were positive for soluble MSLN at diagnosis (Dx) and had a paired serum sample collected at the EOI chemotherapy in the setting of an MRD-negative remission.