The azanucleotides azacitidine and decitabine have been shown to induce hematologic response and prolong survival in higher-risk myelodysplastic syndromes. They are inhibitors of DNA methyltransferase-1 and induce DNA-hypomethylation. Induction of apoptosis is also clinically relevant, in particular during the first treatment cycles, when cytopenia is a frequent side-effect. Since the hypomethylating effect is reversible, and the malignant clone has been shown to persist in most responding patients, several cycles are necessary to achieve and maintain responses, while treatment interruption is associated with rapid relapse. Methylation studies have shown global and gene-specific hypermethylation in myelodysplastic syndromes, but there seems to be little relation between the degree of demethylation following hypomethylating treatment and hematologic response. The presence of concurrent genomic hypermethylation and hypomethylation may impair the predictive power of current detection techniques. This scenario has been complicated by the identification of epigenetic enzyme mutations, including TET2, IDH1/2, DNMT3A and EZH2, which are important for response to hypomethylating treatment. Changes in azanucleotide metabolism genes may also play a role. In the future, methylation analysis concentrating not only on promoters, but also on gene bodies and intergenic regions, may identify key genes in patients with the highest probability of response to azanucleotides and allow a patient-tailored approach.

Therapy-related myeloid neoplasms (t-MNs) include diseases onsetting in patients treated with chemo- and/or radiotherapy for a primary cancer, or an autoimmune disorder. Genomic variants, in particular, in familial cancer genes, may play a predisposing role. Recent advances in deep sequencing techniques have shed light on the pathogenesis of t-MNs, identifying clonal hematopoiesis of indeterminate potential (CHIP) as a frequent first step in the multihit model of t-MNs. CHIP is often detectable prior to any cytotoxic treatment, probably setting the fertile genomic background for secondary leukemogenesis. The evolution pattern toward t-MNs is then a complex process, shaped by the type of cancer therapy, the aging process, and the individual exposures, that favor additional hits, such as the acquisition of TP53 mutations and unfavorable karyotype abnormalities. The pathogenesis of t-MNs differs from MN associated with environmental exposure. Indeed, the genetic aberration patterns of MN developing in atomic bomb survivors show few mutations in classical DNA methylation genes, and a high prevalence of 11q and ATM alterations, together with TP53 mutations. Survival in t-MNs is poor. In addition to the biology of t-MNs, the patient’s previous disease history and the remission status at t-MN diagnosis are significant factors contributing to unfavorable outcome. New drugs active in secondary leukemias include CPX-351, or venetoclax in combination with hypomethylating agents, monoclonal antibodies as magrolimab, or targeted drugs against pathogenic mutations. Allogeneic stem cell transplantation remains the best currently available therapeutic option with curative intent for fit patients with unfavorable genetic profiles.

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood. About 25% of RMS expresses fusion oncoproteins such as PAX3/PAX7-FOXO1 (fusion-positive, FP) while fusion-negative (FN)-RMS harbors RAS mutations. Radiotherapy (RT) plays a crucial role in local control but metastatic RMS is often radio-resistant. HDAC inhibitors (HDACi) radio-sensitize different cancer cells types. Thus, we evaluated MS-275 (Entinostat), a Class I and IV HDACi, in combination with RT on RMS cells in vitro and in vivo. MS-275 reversibly hampered cell survival in vitro in FN-RMS RD (RASmut) and irreversibly in FP-RMS RH30 cell lines down-regulating cyclin A, B, and D1, up-regulating p21 and p27 and reducing ERKs activity, and c-Myc expression in RD and PI3K/Akt/mTOR activity and N-Myc expression in RH30 cells. Further, MS-275 and RT combination reduced colony formation ability of RH30 cells. In both cell lines, co-treatment increased DNA damage repair inhibition and reactive oxygen species formation, down-regulated NRF2, SOD, CAT and GPx4 anti-oxidant genes and improved RT ability to induce G2 growth arrest. MS-275 inhibited in vivo growth of RH30 cells and completely prevented the growth of RT-unresponsive RH30 xenografts when combined with radiation. Thus, MS-275 could be considered as a radio-sensitizing agent for the treatment of intrinsically radio-resistant PAX3-FOXO1 RMS.

Therapy-related myeloid neoplasms (t-MNs) are a complication of cytotoxic treatment for primary tumors and autoimmune diseases. t-MNs result from a complex interaction between individual predisposition and exposition to toxic agents. Some different biological and clinical characteristics can be recognized according to the type of anticancer drug. Compared to de novo myeloid neoplasms, prognosis of t-MN is dismal. Age and karyotype are the most important prognostic factors for t-MN, which should be treated with frontline chemotherapy treatments that are appropriate for patients with myelodysplastic syndrome (MDS) and de novo acute myeloid leukemia (AML) with similar disease characteristics. Allogeneic stem cell transplantation should be considered particularly for unfavorable karyotypes and younger patients with aggressive disease.