Chromosomal instability in medullary carcinoma of the thyroid

No evidence of increased chromosomal aberrations and micronuclei in lymphocytes from nonfamilial thyroid cancer patients prior to radiotherapy

The relationship between the presence of high frequencies of chromosomal aberrations in peripheral lymphocytes and predisposition to cancer has been suggested for some cancer diseases. In nonfamilial thyroid cancer, the few reports available are equivocal. The aim of this study was to assess the possible chromosomal instability in peripheral blood lymphocytes from 22 patients suffering from nonfamilial thyroid cancer. For this purpose, 2 classic cytogenetic assays, the chromosomal aberrations assay and cytokinesis-blocked micronucleus assay, were chosen. The frequency of chromosomal aberrations excluding gaps (%) was 1.68 +/- 1.39 (mean value +/- SD) for the patients group versus 2.20 +/- 1.87 for the control group. The frequency of binucleated lymphocytes with micronuclei ( per thousand) was 5.41 +/- 3.51 (mean value +/- SD) for the patients group versus 5.37 +/- 3.21 for the control group. The results obtained revealed no significant differences between both groups. The present study reinforces the idea that constitutional chromosomal instability in peripheral blood lymphocytes is not visible in nonfamilial thyroid carcinomas.

Spontaneous chromosomal aberrations in cell cultures from patients with neurofibromatosis 1

Neurofibroma-derived cell cultures, skin fibroblast strains from NF1 patients, melanocyte cultures from café-au-lait spots and melanocytes from skin overlying neurofibroma were investigated with regard to the frequencies of spontaneous chromosomal aberrations. A 3.4-fold increased rate of stable and unstable chromosome aberrations in 34 neurofibroma cultures of 18 NF1 patients was noticed in comparison to 17 skin biopsy-derived cultures of healthy probands. Fibroblast strains from the unaffected skin of nine NF1 patients revealed a 2.6-fold higher rate of chromosome breakage compared with the control cultures. Likewise, an increase of spontaneous chromosomal instability by a factor of 13.5 was found in cultured melanocytes from café-au-lait spots and by a factor of 11.9 in the skin-melanocyte cultures of six NF1 patients in comparison to foreskin-derived melanocyte strains of five unaffected persons. Analyses of the distribution of chromatid and chromosome breaks along the chromosomes revealed a significant clustering of these events in the centromeric regions specifically in the four kinds of NF1-derived cultures.

Cytogenetic abnormalities in cancer: with special emphasis on tumor heterogeneity

There is a considerable amount of cytogenetic data available to support the statements that (1) cancer is a genetic disease; (2) most cancers are monoclonal in origin; (3) tumor cells are more genetically unstable than normal cells; (4) the genetic instability may be inherited, acquired, or both during the lifespan of the individual tumor; (5) tumor metastasis is a nonrandom, controlled process, and clonal in origin; (6) malignant tumors are genetically heterogeneous and contain multiple subpopulations that may differ in their biological properties; (7) some tumors might be difficult to treat successfully because of their resistant nature; and (8) tumor cells may acquire resistance because of gene amplification. For these reasons it is extremely important to study the biology of malignant tumor cells in order to determine their effective treatments and control this dreadful disease.

Constitutional chromosome instability and cancer risk

Acquired, clonal chromosome abnormalities are thought to be of pathogenetic importance in human cancer; at the cellular level, neoplasia is best viewed as a genetic disease. It is therefore logical to suggest that cancer risk must somehow be related to individual variations in genomic stability. Those persons whose chromosomes are less stable will, on average, be the ones who are most likely to develop cancer. The testing of this hypothesis shows that, apart from the autosomal recessive chromosome breakage syndromes, only patients with adenomatosis of the colon and rectum have, consistently and by different groups, been found to display elevated spontaneous and clastogen-induced chromosome breakage frequencies. Some evidence indicates a similar tendency in patients with dysplastic nevus syndrome, basal cell carcinoma, cervix cancer, and Kaposi's sarcoma. For several other cancers the data strongly argue against any inherent genomic instability. Although most results thus fail to support constitutional chromosome fragility as a factor of importance in tumorigenesis, conclusive falsification of the hypothesis cannot be said to have been obtained. The possibility remains that variations in chromosome stability and clastogen sensitivity between different cell types, and also difficulties in selecting the most appropriate carcinogens in clastogen-exposure tests, may have masked systematic constitutional differences between patients and controls in the breakage assays.

Effects of age, sex and multiple endocrine neoplasia type-II on silver stained nucleolar organizer regions

Silver stained nucleolar organizer regions (AgNORs) were studied in phytohemagglutinin (PHA)-stimulated lymphocytes from 55 Caucasian control individuals (34 females with average age of 24 years and age range 19 weeks gestation to 87 years; 21 males with average age of 31 years and age range 29 weeks gestation to 72 years) and 13 individuals (7 females, 6 males; average age 38.8 years with age range 25-58 years) with multiple endocrine neoplasia-type II (MEN-II), an autosomal dominant malignancy with increased chromosome breakage. For the first time, AgNORs were examined in lymphocytes from normal fetuses and patients with MEN-II in order to determine the effects of age, sex or malignancy on the number of AgNORs. No significant difference in the average number of AgNORs were found in fetal cells (8.2 +/- S.D. 0.7/cell) when compared with cells from older individuals including those over 65 years of age (8.0 +/- S.D. 0.8/cell). There was a statistically significant negative correlation (P less than 0.05) between the modal number of AgNORs on G but not D chromosomes in both males and females. A negative correlation was also found between the mean number of AgNORs and age but was not statistically significant. The average number of AgNORs in the MEN-II individuals was 8.5 +/- S.D. 0.7/cell, which was not significantly different than 8.2 +/- S.D. 0.7/cell observed in age-matched control subjects.

Cytogenetic studies of individuals from four kindreds with multiple endocrine neoplasia type II syndrome

Multiple endocrine neoplasia type II (MEN-II) syndrome is an autosomal dominant condition characterized by medullary carcinoma of the thyroid, pheochromocytoma, and parathyroid adenoma. A cytogenetic investigation was conducted on 13 MEN-II syndrome patients from four unrelated kindreds and 13 age-matched control subjects for chromosome instability and the chromosome 20 deletion reported in MEN-II syndrome. A significant increase (p less than 0.05) was found in the total number of chromatid and chromosome aberrations in MEN-II cells (12.3%) compared with control cells (6.9%) grown at 96 hours in mitomycin C (20 ng/ml, final concentration). The major difference between the two groups was in chromatid, and not chromosome, aberrations. There was no difference between MEN-II and control individuals in fragile site expression, the number of sister chromatid exchanges or cell kinetics. A blind analysis of high-resolution G-banded chromosomes was performed on blood specimens from 13 MEN-II and seven control individuals. Twelve of 13 MEN-II patients and one of seven control subjects were scored as having a 20p12.2 deletion (chi 2 = 12.6; p less than 0.001). Additional research is needed to determine if this cytogenetic finding is due to a chromosome deletion, inversion, or polymorphism.

Cytogenetic studies on patients with medullary carcinoma of the thyroid

Cytogenetic studies were carried out on stimulated lymphocyte cultures of patients with medullary carcinoma of the thyroid. Of 32 patients studied, seven had a hereditary carcinoma, and five had multiple endocrine neoplasia type 2A and two had type 2B. Neither a constitutional chromosome abnormality nor an increase in chromosomal breakage were detected in these patients.

High resolution chromosome and DNA analysis in multiple endocrine neoplasia type II syndrome

Multiple endocrine neoplasia type II (MEN-II or Sipple's syndrome) is an autosomal dominant disorder characterized by medullary thyroid cancers, pheochromocytomas, and parathyroid adenomas. A blind analysis of high resolution G-banded chromosomes was performed on blood specimens from eight MEN-II individuals from three unrelated families and six control subjects. Seven of eight MEN-II patients and one of six control subjects were determined to have a deletion at 20p12.2. These findings support the hypothesis that MEN-II patients have a 20p12.2 deletion (chi 2 = 6.99; p less than 0.01). Genomic DNA from seven of the eight MEN-II patients was studied using the DNA probe, D20S5, localized by in situ hybridization to 20p12. The probe binding site is not deleted in some MEN-II patients, as demonstrated by the presence of two alleles detected as restriction fragment length polymorphisms. Thus, D20S5 does not hybridize to DNA sequences that are deleted based on cytogenetic analysis in MEN-II patients.