A precision medicine approach to the myelodysplastic syndrome with isolated deletion 5q, 50 years after its discovery.

In 1974, Van den Berghe et al described a distinct hematologic disorder associated with acquired, interstitial deletion of part of the long arm of chromosome 5. This condition is now classified as myelodysplastic syndrome (MDS) with isolated deletion 5q, or MDS-del(5q). The common deletion region 5q32-5q33 contains several genes and microRNAs whose expression levels are reduced in hematopoietic cells, consistent with the loss of 1 allele. Haploinsufficiency production of multiple gene transcripts, primarily involving CSNK1A1, RPS14, MIR145, and MIR146A, results in myelodysplastic hematopoiesis. Lenalidomide can selectively suppress the del(5q)-mutant clone by promoting proteasomal degradation of casein kinase 1A1 and inducing mutant stem cell failure. However, lenalidomide is not a curative treatment, as almost all patients relapse. Molecular profiling studies have significantly improved our understanding of MDS-del(5q). Only a minority of patients have interstitial deletion 5q as their sole genetic lesion, a condition that is associated with an indolent clinical course. Most patients have co-occurring somatic mutations in myeloid genes, including DNMT3A, TET2, ASXL1, SF3B1, TP53, RUNX1, and CSNK1A1. These comutations have independent effects on leukemic transformation and survival, so genomic profiling is required for implementing a precision management approach to MDS-del(5q) in a clinical setting. Accurate assessment of the TP53 allelic state is crucial for distinguishing MDS-del(5q) from TP53-mutant MDS, a myeloid malignancy characterized by TP53 multihit state and very aggressive clinical course. Genomic profiling is also critical for therapeutic decision-making in patients with MDS-del(5q), particularly for assessing a patient's eligibility for allogeneic transplantation, which remains the only curative treatment.