AKT1 and AL amyloidosis: Since previous work demonstrated the utility of pS6 in cytometry-based multiple myeloma CTC assays [50] and because the addition of an extra MM biomarker could potentially help identify a subpopulation of CD138neg/CD45neg MM CTCs, we multiplexed the MM CTC assay to include pS6 as a marker for PI3K/AKT pathway activation.