Background: Even 25 years after the Chernobyl catastrophe, the interpretation of the findings on leukemia risk among Chernobyl clean-up workers is still a point of much controversy. Precise diagnosis of the main types of hematopoietic malignancies according to FAB classification and new WHO classification may be helpful in estimating the relative contribution of the radiation factor to the overall incidence of such pathologies. Methods:The data on 295 consecutive cases of malignant tumors of hematopoietic and lymphoid tissues in Chernobyl clean-up workers diagnosed from 1996 to 2010 are given in comparison with the data of 2,697 consecutive patients other than clean-up workers of the same age group. For this study, a set of complex diagnostic techniques were used, including morphology, cytochemistry of bone marrow and peripheral blood cells, immunocytochemistry (APAAP, LSAB-AP) as well as the utilization of monoclonal antibodies to lineage specific and differentiation antigens of leukocytes.Results: All the main forms of tumors of hematopoietic and lymphoid tissues were diagnosed among clean-up workers under study in 10-25 years after the Chernobyl catastrophe including myelodysplastic syndromes (MDS), acute leukemias (ALL and AML), chronic myelogenous leukemia (CML) and other myeloproliferative neoplasms, chronic lymphocytic leukemia (B-CLL) and lymphoid neoplasms of B and T cell origin. Among 46 AML cases in clean-up workers, leukemia was preceded by MDS in seven patients. CML percentage tended to be higher in the group of patients representing clean-up workers (9.13% vs. 6.59%). B-CLL was a predominant form of hematopoietic malignancies in clean-up workers under study (26.10%). Nevertheless, the percentage of B-CLL in patients of clean-up workers group did not differ significantly from that in the non-exposed patients. The multiple myeloma percentage in our study was higher in the clean-up workers (6.46% vs. 4.00%). Conclusions:The verified diagnosis of tumors of hematopoietic and lymphoid tissues according to the up-to-date WHO classification could be prerequisite for further molecular genetics and analytical epidemiology study of leukemias that may be related to the Chernobyl catastrophe.

The studies of the recent decades posed the question of the association between radiation exposure and myelodysplastic syndromes (MDS). This association has been proved in secondary MDS originating upon exposure to chemotherapeutics and/or radiation therapy. The long-term study in Japanese atomic (A)-bomb survivors demonstrated the significant linear dose-response for MDS confirming the link between radiation exposure and this form of hematopoietic malignancies. All these findings provide the strong basis for studying MDS in the persons exposed to radiation following the Chernobyl disaster, especially those in the cohort of Chernobyl clean-up workers of 1986-1987. The data on MDS among Chernobyl clean-up workers (1986-1987) diagnosed in 1996-2012 at the reference laboratory of RE Kavetsky Institute of Experimental Pathology, Oncology and Radiobiology are summarized. MDS cases were diagnosed in 23 persons (21 males and 2 females) having been exposed to radiation as clean-up workers of 1986-1987. Refractory anemia (RA) has been detected in 13, refractory anemia with ring sideroblasts (RARS)-in 2, and refractory anemia with excess blasts (RAEB)-in 8 patients. The median age of those MDS patients was 62.0 years. In addition, 5 cases of chronic myelomonocytic leukemia (CMML) were recorded in the group of Chernobyl clean-up workers with the median time of 14.8 years from 1986-1987 to diagnosis. The association between radiation exposure and MDS is discussed. The suggested life-long risk for myelodysplastic syndromes among A-bomb survivors in Japan highlights the importance of the continuing follow-up studies in the affected populations in the post-Chernobyl period.

Objective:Nuclear factor kappa B (NF-κB) is an important transcription factor in cancer and NF-κB activation has been seen in angiogenesis, tumor progression, and metastasis. Relationships between specific NF-κB gene networks, leukemogenesis, and radiation exposure are still unknown. Our aim was to study the expression levels of the NF-κB1, NF-κB2, and Rel genes in hematological malignancies in the post-Chernobyl period.Materials and Methods:We analyzed gene expression levels of NF-κB1, NF-κB2, and Rel in 49 B-cell chronic lymphocytic leukemia, 8 B-cell non-Hodgkin’s lymphoma, 3 acute myeloid leukemia, 3 chronic myeloid leukemia, 2 hairy cell leukemia, 2 myelodysplastic syndrome, and 2 T-cell large granular lymphocytic leukemia patients using real-time polymerase chain reaction.Results:Expression levels of NF-κB1, NF-κB2, and Rel genes were found to be deregulated.Conclusion:These results could be accepted as specific gene traces to radiation-induced leukemia or as potential candidates for new diagnostic biomarker studies. Larger experiments and non-exposed control malignant cell populations are needed to clarify these suggestions.

Exposure to ionizing radiation is associated with increasing risk of various types of hematological malignancies. The results of major studies on association of leukemias and radiation exposure of large populations in Japan and in Ukraine are analyzed. The patterns of different types of leukemia in 295 Chernobyl clean-up workers diagnosed according to the criteria of up-to-date World Health Organization classification within 10–25 years following Chernobyl catastrophe are summarized. In fact, a broad spectrum of radiation-related hematological malignancies has been revealed both in Life Span Study in Japan and in study of Chernobyl clean-up workers in Ukraine. The importance of the precise diagnosis of tumors of hematopoietic and lymphoid tissues according to up-to-date classifications for elucidating the role of radiation as a causative factor of leukemias is emphasized. Such studies are of high importance since according to the recent findings, radiation-associated excess risks of several types of leukemias seem to persist throughout the follow-up period up to 55 years after the radiation exposure.