Unclassified Chromosomal Abnormalities as an Indicator of Genomic Damage in Survivors of Hodgkin's Lymphoma.

: Hodgkin's lymphoma (HL) affects 2-4 individuals per 100,000 annually. Standard treatment includes radiotherapy and ABVD chemotherapy, achieving a 95% survival rate. However, HL survivors face an elevated risk of treatment-related morbidity, particularly the development of secondary malignancies. Previous studies have demonstrated that ABVD treatment induces a high frequency of chromosomal aberrations (CAs) in lymphocytes from HL patients, with higher frequencies one year after treatment than during treatment. This study aimed to determine whether HL treatment also induces unclassified chromosomal/nuclear aberrations (UnCAs) in the lymphocytes of HL patients, and whether these alterations may serve as complementary indicators of genomic instability. : Peripheral blood lymphocytes from HL patients were collected at three time points: before treatment (BT), during treatment (DT), and one year after treatment (1yAT) with ABVD chemotherapy and radiotherapy. A minimum of 3000 nuclei were analyzed per patient to identify and quantify UnCAs. These results were compared to UnCA frequencies in healthy individuals. : The percentage of cells presenting UnCAs per 3000 nuclei was 23.92% BT, 18.58% DT, and 30.62% 1yAT. All values were significantly higher ( < 0.016) than the 8.16% observed in healthy controls. The increase was primarily driven by free chromatin and micronuclei clusters. UnCA frequency was lower during treatment than one year after, likely due to the elimination of highly damaged cells through apoptosis or lack of proliferative capacity. Over time, however, persistent genomic damage appears to accumulate in surviving cells, becoming more evident post-treatment. A parallel trend was observed between the frequencies of UnCAs free chromatin, micronucleus and micronuclei clusters, and classical CAs, showing a similar pattern of genomic damage induced by therapy. : The post-treatment increase in UnCAs indicates ongoing genomic instability, possibly driven by the selective survival of hematopoietic stem cells with higher genomic fitness. Given their persistence and association with therapy-induced damage, free chromatin and micronuclei clusters may serve as early biomarkers for secondary cancer risk in HL survivors.