Chromosomal aberrations suggestive of mutagen-related leukemia after 21 years of "therapeutic" radon exposure

The cellular and molecular carcinogenic effects of radon exposure: a review

Radon-222 is a naturally occurring radioactive gas that is responsible for approximately half of the human annual background radiation exposure globally. Chronic exposure to radon and its decay products is estimated to be the second leading cause of lung cancer behind smoking, and links to other forms of neoplasms have been postulated. Ionizing radiation emitted during the radioactive decay of radon and its progeny can induce a variety of cytogenetic effects that can be biologically damaging and result in an increased risk of carcinogenesis. Suggested effects produced as a result of alpha particle exposure from radon include mutations, chromosome aberrations, generation of reactive oxygen species, modification of the cell cycle, up or down regulation of cytokines and the increased production of proteins associated with cell-cycle regulation and carcinogenesis. A number of potential biomarkers of exposure, including translocations at codon 249 of TP53 in addition to HPRT mutations, have been suggested although, in conclusion, the evidence for such hotspots is insufficient. There is also substantial evidence of bystander effects, which may provide complications when calculating risk estimates as a result of exposure, particularly at low doses where cellular responses often appear to deviate from the linear, no-threshold hypothesis. At low doses, effects may also be dependent on cellular conditions as opposed to dose. The cellular and molecular carcinogenic effects of radon exposure have been observed to be both numerous and complex and the elevated chronic exposure of man may therefore pose a significant public health risk that may extend beyond the association with lung carcinogenesis.

Genetic diagnosis by comparative genomic hybridization in adult de novo acute myelocytic leukemia

A total of 127 adult de novo acute myelocytic leukemia (AML) patients were analyzed by comparative genomic hybridization (CGH) at diagnosis. Conventional cytogenetic analysis (CCA) showed a normal karyotype in 45 cases and an abnormal karyotype in 56 cases; in the remaining cases, CCA either failed to yield sufficient metaphase cells (19/26) or was not done (7/26). Abnormal CGH profiles were identified in 39 patients (30.7%). DNA copy number losses (61%) were high compared to gains (39%), whereas partial chromosome changes (76%) were more common than whole chromosomes changes (24%). Recurrent losses were detected on chromosomes 7, 5q (comprising bands 5q15 to 5q33), 7q (7q32 approximately q36), 16q (16q13 approximately q21), and 17p, and gains were detected on chromosomes 8, 22, and 3q (comprising bands 3q26.1 approximately q27). Furthermore, distinct amplifications were identified in chromosome regions 21q, 13q12 approximately q13, and 13q21.1. No cryptic recurrent chromosomal imbalances were identified by CGH in cases with normal karyotypes. The concordance between CGH results and CCA was 72.5%. In the remaining cases, CGH gave additional information compared to CCA (20%) and partially failed to identify the alterations previously detected by CCA (7.5%). The majority of discrepancies arose from the limitations of the CGH technique, such as insensitivity to detect unbalanced chromosomal changes when occurring in a low proportion of cells. CGH increased the detection of unbalanced chromosomal alterations and allowed precise defining of partial or uncharacterized cytogenetical abnormalities. Application of the CGH technique is thus a useful complementary diagnostic tool for CCA in de novo AML cases with abnormal karyotypes or with unsuccessful cytogenetics.

Detection of double minute chromosomes in a child with acute lymphoblastic leukemia

A child with acute lymphoblastic leukemia (ALL) whose predominant leukemic clone demonstrated double minute chromosomes (dmin) is presented. The patient had no history of mutagen or carcinogen exposure and responded well to combination chemotherapy. Although dmin have been described in acute myelogenous leukemia and various solid tumors in adults, their presence in childhood neoplasms is less frequent and limited primarily to neurogenic tumors. This is the first documentation of dmin in childhood ALL, suggesting that there may be an unrecognized subgroup of ALL patients with gene amplification.

12p rearrangement and DNA amplification mapped by comparative genomic hybridization in a patient with secondary myeloid leukemia

Rearrangements of the short arm of chromosome 12 (12p) are a common finding in hematologic malignancies. There has recently been considerable interest in chromosome 12 abnormalities in view of the mapping of the TEL gene to 12p13 and frequent 12p interstitial deletions. Overrepresentation of 12p sequences is, on the other hand, a consistent finding in testicular germ cell tumor (TGCT), and the 12p11.2-p12.1 subregion has been found to be specifically involved. We have studied a secondary leukemic patient whose cells contained 12p rearrangements with a view to clarifying the underlying molecular events. Fluorescence in situ hybridization (FISH) and comparative genomic hybridization (CGH) have revealed the presence of 12p11 breakpoints on both 12 homologs as well as amplification of 12p11-p12-derived sequences. Six YACs and a cosmid probe have been used in an attempt to map the amplification unit on 12p. The two YACs contigs WC-1468 and WC-985 were not amplified, and our results suggested a small amplicon localized in the 12p11.2-p12 subregion. We speculate that this region harbors gene(s) which are critical in tumor formation and could be involved in both TGCT and our patient. Whether the same gene(s) are involved in both amplification and translocation is unknown.

Localization of amplified MYC gene sequences to double minute chromosomes in acute myelogenous leukemia

Cytogenetic and molecular studies were performed on two dmin-bearing acute myelogenous leukemia (FAB-M2) samples. Both cases were characterized by complex karyotypes containing interstitial deletions of the long arm of chromosome 8 altering band 8q24.1, aberrations affecting the short arm of chromosome 17, and multiple double minute chromosomes (dmin). Using a 1.4 kb cDNA probe coding for the third exon of the MYC oncogene, DNA slot blots indicated MYC gene sequences were amplified in both samples. Fluorescence in situ hybridization using a 9.0 kb genomic probe for MYC was performed in one case and localized the amplified MYC gene sequences to the dmin. Neither patient achieved a complete remission using traditional induction chemotherapy. The complex karyology with amplification of MYC gene sequences appears to represent a poor prognostic subgroup of acute myelogenous leukemia.

Extrachromosomal gene amplification in acute myeloid leukemia; characterization by metaphase analysis, comparative genomic hybridization, and semi-quantitative PCR

A case of acute myeloid leukemia (M-3) with complex karyotypic aberrations and double minute (dmin) chromosomes is presented. The patient had no history of prior exposure to mutagenic or carcinogenic agents or of other malignancies. She died from CNS involvement six weeks after the initial diagnosis. We used comparative genomic hybridization to identify the amplified sequences presumed to represent the dmin of the leukemic cells; the tumor/normal ratios indicated increased signal intensity at 8q24. This localization prompted investigation by semi-quantitative PCR that revealed amplification of the MYC oncogene. The extent of chromosome aberrations and the oncogene amplification, both linked with poor prognosis, may relate to the rapid course of this patient's disease.