Expression and polymorphism (rs4880) of mitochondrial superoxide dismutase (SOD2) and asparaginase induced hepatotoxicity in adult patients with acute lymphoblastic leukemia.

Asparaginase, which depletes asparagine and glutamine, activates amino-acid stress response. Oxidative stress mediated by excessive reactive oxygen species (ROS) causes enhanced mitochondrial permeabilization and subsequent cell apoptosis and is considered as a plausible mechanism for drug-induced hepatotoxicity, a common toxicity of asparaginase in adults with acute lymphoblastic leukemia (ALL). Studies investigating the pharmacogenetics of asparaginase in ALL are limited and focused on asparaginase-induced allergic reaction common in pediatric patients. Here, we sought to determine a potential association between the variant rs4880 in SOD2 gene, a key mitochondrial enzyme that protects cells against ROS, and hepatotoxicity during asparaginase-based therapy in 224 patients enrolled on CALGB-10102, a treatment trial for adults with ALL. We report that the CC genotype of rs4880 is associated with increased hepatotoxicity following asparaginase-based treatment. Thus, rs4880 likely contributes to asparaginase-induced hepatotoxicity, and functional studies investigating this single-nucleotide polymorphism (SNP) are needed to develop therapeutic approaches that mitigate this toxicity.

Comprehensive mutational analysis of primary and relapse acute promyelocytic leukemia.

Acute promyelocytic leukemia (APL) is a subtype of myeloid leukemia characterized by differentiation block at the promyelocyte stage. Besides the presence of chromosomal rearrangement t(15;17), leading to the formation of PML-RARA (promyelocytic leukemia-retinoic acid receptor alpha) fusion, other genetic alterations have also been implicated in APL. Here, we performed comprehensive mutational analysis of primary and relapse APL to identify somatic alterations, which cooperate with PML-RARA in the pathogenesis of APL. We explored the mutational landscape using whole-exome (n=12) and subsequent targeted sequencing of 398 genes in 153 primary and 69 relapse APL. Both primary and relapse APL harbored an average of eight non-silent somatic mutations per exome. We observed recurrent alterations of FLT3, WT1, NRAS and KRAS in the newly diagnosed APL, whereas mutations in other genes commonly mutated in myeloid leukemia were rarely detected. The molecular signature of APL relapse was characterized by emergence of frequent mutations in PML and RARA genes. Our sequencing data also demonstrates incidence of loss-of-function mutations in previously unidentified genes, ARID1B and ARID1A, both of which encode for key components of the SWI/SNF complex. We show that knockdown of ARID1B in APL cell line, NB4, results in large-scale activation of gene expression and reduced in vitro differentiation potential.

Environmental toxicant-induced germ cell apoptosis in the human fetal testis.

BACKGROUND: Disorders of the male reproductive system are increasing in prevalence. The term testicular dysgenesis syndrome emphasizes the importance of developmental influences on the aetiology of conditions including cryptorchidism, testicular germ cell cancer and reduced spermatogenesis. Men whose mothers smoked during pregnancy have lower sperm production. Cigarette smoke contains agents acting on the aryl hydrocarbon receptor (AHR). We have investigated the presence of AHR in the developing human testis and the effects of functional activation. METHODS AND RESULTS: Immunohistochemistry determined AHR to be expressed by germ cells in the human testis between 7 and 19 week gestation, but not by other cells. Treatment of cultured fetal testis with an AHR ligand present in tobacco smoke increased markers of cell apoptosis, and this was prevented by an AHR receptor antagonist. Immunohistochemistry indicated that apoptosis was restricted to germ cells. CONCLUSIONS: Germ cells in the developing human testis are a target for regulation by AHR ligands. Activation of AHR by environmental toxicants and AHR-induced apoptotic pathways may be the mechanism of action underlying the epidemiological findings of reduced spermatogenesis in men exposed to cigarette smoke before birth, and may also be of importance in other conditions comprising the testicular dysgenesis syndrome.

Developmental changes in expression of myeloid cell leukemia-1 in human germ cells during oogenesis and early folliculogenesis.

The regulation of germ cell number in the developing ovary is central to female reproduction. Members of the Bcl-2 family of proapoptotic and antiapoptotic proteins have been implicated in this process in rodents. We investigated the expression of Mcl-1, Bcl-2, Bax, and BAD at 13-21 gestational wk in the human fetal ovary and of Mcl-1 in the adult ovary. mRNA expression of Mcl-1 and its short form Mcl-1s, Bcl-2, Bax, and BAD was demonstrated in fetal ovary by RT-PCR. Hybridization array analysis suggested a selective increase in Mcl-1 expression between 14 and 18 wk gestation, which was confirmed by quantitative PCR. There was a corresponding change in the expression of Mcl-1 protein, detected by immunohistochemistry, from germ cells at the periphery of the ovary at 14-16 wk to the largest germ cells, including oocytes within newly formed primordial follicles, at 21 wk. Mcl-1 was also expressed by oocytes of primordial and preantral follicles in the adult. Bax and BAD immunostaining was detected in both somatic and germ cells in the fetal ovary, whereas Bcl-2 was restricted to somatic cells: no changes in expression were observed. Apoptotic cells, detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, were observed in all fetal ovaries but were infrequent. These results confirm that Bcl-2 family members are differentially expressed in several cell types within the developing human ovary. Increased mRNA expression and the changing distribution of Mcl-1 in germ cells as they develop into primordial follicles as well as persistence in the growing oocyte in the adult may indicate an important role for this survival/antiapoptotic factor throughout germ cell development and maturation.

A novel nuclear protein, 5qNCA (LOC51780) is a candidate for the myeloid leukemia tumor suppressor gene on chromosome 5 band q31.

Interstitial deletion or loss of chromosome 5, del(5q) or -5, is a frequent finding in myeloid leukemias and myelodysplasias, suggesting the presence of a tumor suppressor gene within the deleted region. In our search for this gene, we identified a candidate, 5qNCA (LOC51780), which lies within a consistently-deleted segment of 5q31. 5qNCA expresses a 7.2-kb transcript with a 5286-bp open reading frame which is present at high levels in heart, skeletal muscle, kidney, placenta, and liver as well as CD34+ cells and AML cell lines. 5qNCA encodes a 191-kD nuclear protein which contains a highly-conserved C-terminus containing a zinc finger with the unique spacing Cys-X2-Cys-X7-His-X2-Cys-X2-Cys-X4-Cys-X2-Cys and a jmjC domain, which is often found in proteins that regulate chromatin remodeling. Expression of 5qNCA in a del(5q) cell line results in suppression of clonogenic growth. Preliminary sequence results in AML and MDS samples and cell lines has revealed a possible mutation in the KG-1 cell line resulting in a THR to ALA substitution that has not been found in over 100 normal alleles to date. We propose 5qNCA is a good candidate for the del(5q) tumor suppressor gene based on its predicted function and growth suppressive activities, and suggest that further mutational and functional study of this interesting gene is warranted.

Highly abundant genes in the transcriptosome of human and baboon CD34 antigen-positive bone marrow cells.

Nonhuman primates are useful large animal model systems for the in vivo study of hematopoietic stem cell biology. To better understand the degree of similarity of the hematopoietic systems between humans and baboons, and to explore the relevance of such studies in nonhuman primates to humans, this study was designed to compare the global gene expression profile of bone marrow CD34(+) cells isolated from these 2 species. Human complementary DNA (cDNA) filter arrays containing 25 920 human cDNAs were surveyed for this purpose. The expression pattern and relative gene abundance of the 2 RNA sources were similar, with a correlation coefficient of 0.87. A total of 15 970 of these cDNAs were expressed in human CD34(+) cells, of which the majority (96%) varied less than 3-fold in their relative level of expression between human and baboon. Reverse transcriptase-polymerase chain reaction analysis of selected genes confirmed that expression was comparable between the 2 species. No species-restricted transcripts have been identified, further reinforcing the high degree of similarity between the 2 populations. A subset of 1554 cDNAs, which are expressed at levels 100-fold and greater than background, is described, which includes 959 expressed sequence tags and uncharacterized cDNAs, and 595 named genes, including many that are clearly involved in hematopoiesis. The cDNAs reported here represent a selection of some of the most highly abundant genes in hematopoietic cells and provide a starting point to develop a profile of the transcriptosome of CD34(+) cells.

Delineation of a minimal interval and identification of 9 candidates for a tumor suppressor gene in malignant myeloid disorders on 5q31.

Interstitial deletion or loss of chromosome 5 is frequent in malignant myeloid disorders, including myelodysplasia (MDS) and acute myeloid leukemia (AML), suggesting the presence of a tumor suppressor gene. Loss of heterozygosity (LOH) analysis was used to define a minimal deletion interval for this gene. Polymorphic markers on 5q31 were identified using a high-resolution physical and radiation hybrid breakpoint map and applied to a patient with AML with a subcytogenetic deletion of 5q. By comparing the DNA from leukemic cells to buccal mucosa cells, LOH was detected with markers D5S476 and D5S1372 with retention of flanking markers D5S500 to D5S594. The D5S500-D5S594 interval, which covers approximately 700 kb, thus represents a minimal localization for the tumor suppressor gene. Further refinement of the physical map enabled the specification of 9 transcription units within the encompassing radiation hybrid bins and 7 in flanking bins. The 9 candidates include genes CDC25, HSPA9, EGR1, CTNNA1, and 5 unknown ESTs. Reverse-transcription polymerase chain reaction confirms that all of them are expressed in normal human bone marrow CD34(+) cells and in AML cell lines and thus represent likely candidates for the MDS-AML tumor suppressor gene at 5q31.

A radiation hybrid breakpoint map of the acute myeloid leukemia (AML) and limb-girdle muscular dystrophy 1A (LGMD1A) regions of chromosome 5q31 localizing 122 expressed sequences.

We have constructed a high-resolution map of a 6-Mb interval of human chromosome 5, band q31, incorporating 175 sequence tagged sites, of which 33 are genetic polymorphisms and 122 are nonredundant expressed sequences. The map was assembled initially as a YAC contig, incorporating data from radiation hybrid maps. To improve resolution and to identify errors in the databases, a radiation hybrid breakpoint map was developed for the interval, which included hybrids from both Stanford G3 and GeneBridge 4 panels. This novel approach facilitated the integration of one RH panel with another and enabled the identification and localization of new, previously unmapped ESTs from the radiation hybrid databases. ESTs were assembled into overlapping transcription units and ordered with respect to polymorphic markers in the region, resulting in a comprehensive map that incorporates markers from multiple different types of maps. This map of 5q31 will facilitate gene discovery efforts for several disorders, including limb-girdle muscular dystrophy type 1A and the genes deleted in acute myeloid leukemias and myelodysplasia. The study demonstrates the utility of a radiation hybrid breakpoint panel for correction of map errors and for the efficient identification of new transcript units in a large genomic interval.

The presence of K-12 ras mutations in duodenal adenocarcinomas and the absence of ras mutations in other small bowel adenocarcinomas and carcinoid tumors.

BACKGROUND: Adenocarcinomas and carcinoid tumors are the most common malignant tumors of the small intestine. K-ras oncogene mutations at codon 12 are common in gastric, pancreatic, and colon carcinomas, with an incidence of 35-88%. K-ras mutations have not been extensively studied in either adenocarcinomas or carcinoid tumors of the small bowel. The purpose of this study was to determine whether ras mutations play an important role in the formation of these tumors. METHODS: Archival tissues from 28 adenocarcinomas and 22 carcinoid tumors of the small bowel were studied, along with archival tissues from 32 adenocarcinomas of the large bowel, which were used as controls. DNA from the small intestine tumors was analyzed for K-ras, H-ras, and N-ras oncogene mutations at codons 12, 13, and 61, using polymerase chain reaction and sequence specific oligonucleotide hybridization techniques. Large bowel adenocarcinomas were analyzed for K-ras mutations at codons 12 and 13. RESULTS: A point mutation of K-ras at codon 12 was detected in 4 of 28 (14.3%) of the small bowel adenocarcinomas, in 12 of 32 (37.5%) of the large bowel adenocarcinomas, and in 0 of 22 small intestine carcinoid tumors. No other K-ras, H-ras, or N-ras mutations were detected in any of the small bowel tumors. Each small intestine K-ras mutation was found in a duodenal adenocarcinoma (4 of 12 cases, 33%), whereas none occurred in 16 other jejunal or ileal adenocarcinomas. CONCLUSIONS: K-ras mutations appear to play a significant role in the pathogenesis of duodenal adenocarcinomas, but they do not appear to be important in the development of jejunal or ileal adenocarcinomas or of carcinoid tumors of the small intestine.

N-ras mutation: an independent prognostic factor for aggressiveness of papillary thyroid carcinoma.

BACKGROUND: The clinical importance of point mutations of ras oncogene in differentiated thyroid cancers has not been fully clarified. The purpose of this study is to determine the prognostic importance of ras mutation in papillary thyroid carcinoma. METHODS: Tumors of 91 patients with papillary carcinoma were studied; mean follow-up was 14.1 years (range, 1 to 40 years). Patients were grouped as follows: class I, intrathyroidal disease, n = 21; class II, cervical node metastases, n = 22; class III, extrathyroidal disease, n = 19; and class IV, distant metastases, n = 29. DNA was analyzed with polymerase chain reaction, oligonucleotide hybridization, and DNA sequence analysis techniques. RESULTS: Thirteen (14.3%) of 91 tumors showed an N-ras point mutation: 4.8% (1 of 21) patients in class I; 4.5% (1 of 22) patients in class II; 15.8% (3 of 19) patients in class III; and 27.8% (8 of 29) patients in class IV. Each mutation changed codon 61 from glutamine to arginine. Patients with distant metastases (8 of 29) had a significantly higher incidence of ras mutations than others (5 of 62, p = 0.01). Patients in classes III and IV also had a higher incidence of mutations (11 of 48) than patients in classes I and II (2 of 43, p = 0.01). The incidence of ras mutations was significantly higher in patients who died of papillary cancer (5 of 15, 33.3%) than in patients who are still alive (8 of 76, 10.5%) (p = 0.02). Kaplan-Meier survival curves also showed a greater mortality from tumor (p < 0.05) and a higher recurrence rate (p < 0.01) in ras-positive tumors than in the ras-negative group. Finally, in studies by multivariate analyses, positive ras mutation and age were shown to be two independent prognostic factors for prediction of death from papillary cancer and recurrence of cancer. CONCLUSIONS: Mutation of N-ras gene at codon 61 is an independent prognostic factor for aggressiveness of papillary thyroid carcinomas.

Point mutations of ras genes in human adrenal cortical tumors: absence in adrenocortical hyperplasia.

Point mutations of ras genes (K-, H-, and N-ras) at codons 12, 13, and 61 and of the Gi2 alpha gene at codons 179 and 205, were studied in 56 primary adrenal cortical tumors and 6 adrenal cortical hyperplasias. Of 56 tumors, 24 were carcinomas and 32 were benign. The 24 carcinomas and 20 of the benign tumors were from American patients; the 12 remaining adenomas were from Japanese patients. Of the benign tumors 12 were cortisol-producing adenomas, 15 were aldosterone-producing adenomas, 3 were nonfunctioning adenomas, and 2 were adenomas that produced a virilizing syndrome. Tumor DNA obtained from archival formalin-fixed, paraffin-embedded tissue or fresh frozen tissue was amplified by polymerase chain reaction; and point mutations were detected by sequence-specific oligonucleotide hybridization. Activating ras mutations were found in 7 of 56 (12.5%) of all tumors: 3 of 24 (12.5%) carcinomas and 4 of 32 (12.5%) adenomas. Of adenomas from an American population, 4 of 20 (20%) exhibited positive ras mutations, whereas none was present in the Japanese tumors. All mutations detected were adenine to guanine transitions at the second position of N-ras codon 61, resulting in a conversion from glutamine to arginine. No mutations were found in K-ras or H-ras genes. Furthermore, no mutations of the Gi2 alpha gene were identified. These findings demonstrate that N-ras mutations at codon 61 may contribute to the genesis of both benign and malignant human adrenal cortical tumors. Finally, no mutations of the ras or Gi2 alpha genes were identified in hyperplastic adrenocortical tissues.

Increased incidence of thyroid cancer in patients with primary hyperparathyroidism: a continuing dilemma.

A number of previous studies have reported a greater incidence of thyroid disease in patients with primary hyperparathyroidism (HPT) than in normal patients. However, few of these studies utilized controls, and most have dealt only with gross thyroid nodules and not with total histologic abnormalities. In order to clarify this problem, thyroid pathology was determined in each of 100 consecutive patients operated upon for HPT. Thyroid nodules were excised, but in addition, a random biopsy of the thyroid was performed in all cases. Patients in this group were matched by age, race, and sex with non-HPT autopsy controls. Histologic slides were reviewed by a single pathologist blinded to the patient's group. Data for the matched pairs were analyzed by the Sign test. There was no significant difference in the prevalence of colloid nodular disease between patients with HPT (45) and the autopsy control group (43, P = 0.2). There was also no significant difference in the prevalence of lymphocytic thyroiditis between HPT patients (24) and control (15, P = 0.07). There was likewise no significant difference in the prevalence of other benign thyroid gland diseases between the two groups. Only nonmedullary cancer of the thyroid was shown to be statistically more prevalent in HPT patients than in autopsy controls (7% vs 0%, respectively; P < 0.02). The major factor that accounts for the coexistence of benign thyroid lesions and HPT is that both are prevalent in middle-aged women.(ABSTRACT TRUNCATED AT 250 WORDS)

K-ras mutations in putative preneoplastic lesions in human colon.

BACKGROUND: A mutation in c-K-ras (KRAS2) has long been implicated as one of the important early events in the development of a large proportion of human colon cancers. Aberrant crypt foci, putative preneoplastic lesions identified microscopically in wholemounts of colons, have been shown to occur with high frequency in the colons of animals treated with colon carcinogens and in the grossly normal mucosas of patients with colon cancer. PURPOSE: In this study, we asked whether the mutational activation of K-ras occurs in the aberrant crypt foci of human colon. METHODS: Grossly normal colonic mucosas were obtained from seven patients during surgery and were provided to us by the Western Division of the Cooperative Human Tissue Network located at Case Western Reserve University. A total of 42 samples, consisting of aberrant crypt foci and similarly sized normal crypt areas, were microdissected from the grossly normal colonic mucosas. The DNA region containing codon 12 of K-ras was amplified by polymerase chain reaction and analyzed for mutations by dot-blot hybridization with specific oligonucleotide probes complementary to normal or mutant sequences. RESULTS: Mutations in codon 12 of K-ras were found in 11 (73%) of 15 aberrant crypt foci but not in any of 27 morphologically normal crypt areas from the same patients. CONCLUSIONS: The observed high frequency of K-ras mutations in these microscopically identifiable lesions makes mutation in K-ras the earliest identified gene-mutational event in human colon tumorigenesis, establishes that it often occurs prior to the development of polyps, and is consistent with the hypothesis that aberrant crypt foci are the earliest identified precursors of human colon cancer. IMPLICATIONS: Further analysis of aberrant crypt foci may identify yet unknown early genetic events that precede human colon cancer.

Comparison of mutations of ras oncogene in human pancreatic exocrine and endocrine tumors.

BACKGROUND: Ras oncogene mutations have been found in many human cancers; however, pancreatic endocrine tumors have rarely been studied. The purpose of this study was to analyze ras mutations in pancreatic endocrine tumors and to compare these results with the incidence of ras mutations in pancreatic exocrine cancers studied in our laboratory. METHODS: Ras oncogene mutations were studied in 33 foregut endocrine tumors (pancreatic 31, duodenal submucosa 2). Eleven were insulinomas, 12 gastrinomas, 2 glucagonomas, and 11 others were nonfunctioning islet cell carcinomas. Thirteen were benign and 20 were malignant. These were compared with 65 pancreatic exocrine cancers. Tumors were microdissected from paraffin-embedded sections. DNA was extracted and amplified by polymerase chain reaction. Mutations were detected by a oligonucleotide hybridization method with sequence-specific phosphorus 32-radiolabeled probes. RESULTS: No ras mutations were identified among the 33 pancreatic endocrine tumors. In contrast, 51 of 65 (78.5%) pancreatic exocrine cancers exhibited a ras mutation. Fifty were K-ras mutations and one unusual tumor exhibited a N-61 ras mutation. CONCLUSIONS: Ras oncogene mutations do not play a role in the tumorigenesis of pancreatic endocrine tumors.

The value of measurement of ras oncogenes and nuclear DNA analysis in the diagnosis of Hürthle cell tumors of the thyroid.

Hürthle cell tumors (HCT) remain difficult to treat because some which appear non-malignant on light microscopy later metastasize. In order to improve diagnostic accuracy, the value of ras mutations and nuclear DNA analysis was determined in 65 patients with HCT. Rapid nuclear DNA cytometry (MicroTICAS system) was performed. Mutations of H-ras, K-ras, and N-ras genes were analyzed by oligonucleotide probe hybridizations to polymerase chain reaction (PCR) amplified DNA. HCT were classified by light microscopy as benign (n = 22), intermediate (n = 30), and malignant (n = 13). After a mean follow-up of 7 years, 1 (4.5%) of 22 benign tumors and 4 (13%) of 30 intermediate tumors had metastasized, leading to tumor death in 3 of these 5 patients. Six of the 13 cancers diagnosed by light microscopy also resulted in tumor-related deaths. Aneuploidy was found in 83% of all Hürthle cell cancers, including 3 (60%) of the 5 cancers not diagnosed microscopically. However, 49% of non-malignant HCT also demonstrated aneuploidy. A nuclear area of less than 55 square microns was found in 83% of all Hürthle cell cancers and in 100% of those cancers not diagnosed by light microscopy. However, 47% of non-malignant HCT also demonstrated a "small" nuclear area. Aneuploidy correctly identified 8 of 9 cancers that resulted in tumor death and each of 3 other tumors that developed metastases. However, 1 patient with a diploid tumor died of metastatic cancer. A nuclear area of less than 55 square microns identified each cancer that resulted in a tumor death.(ABSTRACT TRUNCATED AT 250 WORDS)

Continuing evolution in the operative management of primary hyperparathyroidism.

During the past several decades the operation for primary hyperparathyroidism at The University of Chicago, Ill, has changed from subtotal parathyroidectomy for all patients to removal of an adenoma with performance of biopsies of all other glands to bilateral neck exploration, resection of the adenoma, and performance of fewer biopsies of normal glands. During the 1980s, 308 operations were performed; 288 patients underwent first operations. Two hundred forty-five (85.1%) of these patients had an adenoma and forty-three (14.9%) had hyperplasia (multiglandular disease); none had a carcinoma. Resolution of hypercalcemia was achieved in 281 patients (97.5%); seven patients experienced failed explorations. The early cure was the same whether or not preoperative localization studies were performed. Nineteen patients underwent 20 reoperative parathyroidectomies during this period. Preoperative localization studies, done in 16 (80%) of 20 cases, were very helpful. Ninety percent of patients with abnormal parathyroid glands in their neck or mediastinum were cured with their initial reoperation.

N-ras 61 oncogene mutations in Hürthle cell tumors.

Mutations of ras oncogenes are believed to play an important role in the initiation or progression of human tumors. In thyroid tumors the incidence of ras activation by specific point mutations has been reported to range from 33% in follicular adenomas up to 60% in anaplastic carcinomas. Because of our long-standing interest in Hürthle cell tumors, we began a study of 70 such cases to determine the incidence of ras mutations and their clinical correlates. Analysis of N-ras sequences at codon position 61, with the polymerase chain reaction method and oligonucleotide probe hybridization, showed point mutations of the normal codon CAA* in eight tumor samples. One was a mutation from CAA to AAA, one from CAA to CTA,* and six from CAA to CGA. These mutations would result in amino acid substitutions of lysine, leucine, or arginine for the normal glutamine at position 61 in the N-ras protein. Identical ras mutations in two tumors and some of their surrounding thyroid tissue may indicate that activating ras point mutations are an early event in carcinogenesis. The incidence of mutations was 1 of 24 (4%) of the histologically benign tumors, 5 of 34 (15%) of the intermediate tumors (with vascular or capsular permeation), and 2 of 12 (17%) in the malignant group. Four of these eight patients died of metastatic thyroid disease and four are alive without evidence of recurrence.

Difficulties of parathyroidectomy after previous thyroidectomy.

Although the risks of reoperative thyroidectomy and parathyroidectomy have been well studied, the problems associated with parathyroidectomy after prior thyroidectomy have not been emphasized. Among a group of 282 patients who were treated for primary hyperparathyroidism in recent years at the University of Chicago Medical Center, 14 (4.8%) had undergone one or more previous thyroidectomies, and 6 others (2.1%) had undergone thyroid ablation with radioactive iodine as therapy for Graves' disease. Numerous difficulties were encountered during surgery in the postthyroidectomy group of patients as a result of scarring and fibrosis, prior recurrent laryngeal nerve injuries in 13%, the inability to known with certainty how many viable, normal parathyroid glands remained after previous operations, and the need for additional thyroid resection, mostly for associated malignant lesions. Preoperative vocal cord assessment, evaluation of prior operative and pathology reports, and localization studies with thallium-technetium scanning and ultrasonographic techniques were especially helpful. A "lateral approach" was used frequently during surgery. Each of these 14 patients was cured of the hyperparathyroidism. The postthyroid ablation group presented fewer intraoperative challenges, although in some patients the thyroid gland was virtually absent, which obscured the normal landmarks of the surgical field. Five of these six patients were cured of hyperparathyroidism. Parathyroidectomy after thyroidectomy presents many operative challenges to the surgeon and should be approached with the same care and concern that one reserves for a reoperative parathyroid operation.