Therapy-related myelodysplastic syndrome and acute myeloid leukemia (t-MDS/AML) has been reported after treatment of Hodgkin lymphoma (HL), acute lymphoblastic leukemia (ALL), and sarcomas, with the cumulative incidence approaching 2% at 15 years after therapy.[8,9,10,11] Some cases of late recurrence among childhood acute lymphoblastic leukemia have been shown to represent cases of new primary leukemia based on TCR gene rearrangement.[12,13] t-MDS/AML is a clonal disorder characterized by distinct chromosomal changes. The following two types are recognized by the World Health Organization classification:
- Alkylating agent-related type: Alkylating agents associated with t-MDS/AML include cyclophosphamide, ifosfamide, mechlorethamine, melphalan, busulfan, nitrosoureas, chlorambucil, and dacarbazine. The risk of alkylating agent–related t-MDS/AML is dose dependent, with a latency of 3 to 5 years after exposure; it is associated with abnormalities involving chromosomes 5 (-5/del[5q]) and 7 (-7/del[7q]).
- Topoisomerase II inhibitor-related type: Most of the translocations observed in patients exposed to topoisomerase II inhibitors disrupt a breakpoint cluster region between exons 5 and 11 of the band 11q23 and fuse mixed lineage leukemia with a partner gene. Topoisomerase II inhibitor-related t-AML presents as overt leukemia after a latency of 6 months to 3 years and is associated with balanced translocations involving chromosome bands 11q23 or 21q22.
Therapy-Related Solid Neoplasms
Therapy-related solid SNs represent 80% of all SNs and demonstrate a strong relationship with ionizing radiation. The histological subtypes of solid SNs encompass a neoplastic spectrum ranging from benign and low-grade malignant lesions (e.g., NMSC, meningiomas) to high-grade malignancies (e.g., breast cancers, glioblastomas).[1,11,16,17,18] SN solid tumors in childhood cancer survivors most commonly involve the breast, thyroid, central nervous system (CNS), bones, and soft tissues.[1,8,11,17,19] With more prolonged follow-up of cohorts of adults surviving childhood cancer, epithelial neoplasms involving the gastrointestinal tract and lung have emerged.[1,8,16] Benign and low-grade SNs, including NMSCs and meningiomas, have also been observed with increasing prevalence in survivors treated with radiation for childhood cancer.[1,17,18]