NF-κB-mediated transcriptional upregulation of TNFAIP2 by the Epstein-Barr virus oncoprotein, LMP1, promotes cell motility in nasopharyngeal carcinoma.

Nasopharyngeal carcinoma (NPC), which is closely associated with Epstein-Barr virus (EBV), is a metastasis-prone epithelial cancer. We previously showed that tumor necrosis factor α-induced protein 2 (TNFAIP2) is highly expressed in NPC tumor tissues and is correlated with metastasis and poor survival in NPC patients. However, the underlying mechanism remains unclear. In this study, we demonstrate that the EBV oncoprotein, latent membrane protein 1 (LMP1), can transcriptionally induce TNFAIP2 expression via NF-κB. Quantitative RT-PCR and western blotting revealed that LMP1 induces TNFAIP2 expression through its C-terminal-activating region (CTAR2) domain, which is required for transduction of NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) signaling. Inhibition of NF-κB activation or depletion of p65 (a component of NF-κB) by RNA interference abolished the LMP1-induced expression of TNFAIP2, whereas ectopic expression of p65 was sufficient to induce TNFAIP2 expression. Luciferase reporter assays showed that LMP1 transcriptionally induces TNFAIP2 expression through a newly identified NF-κB-binding site within the TNFAIP2 promoter (-3,869 to -3,860 bp). Immunohistochemical analysis of NPC biopsy specimens further revealed a significant correlation between the protein levels of TNFAIP2 and activated p65 (R=0.689, P<0.001), indicating that our findings are clinically relevant. Immunofluorescence microscopy and co-immunoprecipitation assays showed that TNFAIP2 associates with actin and is involved in the formation of actin-based membrane protrusions. Furthermore, transwell migration assays demonstrated that TNFAIP2 contributes to LMP1-induced cell motility. Collectively, these findings provide novel insights into the regulation of TNFAIP2 and its role in promoting NPC tumor progression.

Clinical presentations of thyroid cancer patients with multiple primary cancers.

BACKGROUND: In thyroid cancer patients with multiple primary cancers, primary cancers tend to be more aggressive. AIMS: We analyzed multiple primary cancers in thyroid cancer patients and determined the differences between the incidence and the characteristics of primary cancers. MATERIALS AND METHODS: A total of 3070 patients with thyroid cancer underwent a thyroidectomy and follow-up examination at a single medical center. The times of diagnosis of the primary cancers were categorized as antecedent, synchronous, or subsequent to the diagnosis of thyroid cancer. RESULTS: After a mean follow-up period of 8.8 ± 0.5 yr, the presence of multiple primary cancers was histopathologically confirmed in 163 patients (5.3%). Patients with multiple primary cancers had a lower female-to-male ratio, an older mean age, advanced tumor-node-metastasis (TNM) stage, higher total mortality, and higher therapeutic radioactive iodide (131I) doses than patients without multiple primary cancers. Hematological malignancy and renal cell carcinoma, neither of which are among the 10 most common cancers observed in the general population of Taiwan, were the most common multiple cancers among women and men with thyroid cancer. Patient age, thyroid cancer tumor size, and thyroid cancer mortality in the antecedent, synchronous, and subsequent groups were not significantly different. CONCLUSIONS: Patients with multiple primary cancers in advanced stages had shorter disease-free survival period after treatment. Thyroid cancer patients with multiple primary cancers should be closely followed up for the occurrence of other secondary cancers in order to improve total mortality.

The antiapoptotic protein, FLIP, is regulated by heterogeneous nuclear ribonucleoprotein K and correlates with poor overall survival of nasopharyngeal carcinoma patients.

Heterogeneous nuclear ribonucleoprotein K (hnRNP K) mediates antiapoptotic activity in part by inducing downstream antiapoptotic genes. To systematically identify hnRNP K targets in nasopharyngeal carcinoma (NPC), affymetrix chips were used to identify genes that were both overexpressed in primary NPC and downregulated by hnRNP K knockdown in NPC-TW02 cells. The resulting gene set included the antiapoptotic gene, FLIP, which was selected for further study. In cells treated with hnRNP K siRNA, TRAIL-induced apoptosis was enhanced and the FLIP protein level was reduced. Promoter, DNA pull-down and chromatin-immunoprecipitation assays revealed that hnRNP K directly interacts with the poly(C) element on the FLIP promoter, resulting in transcriptional activation. Through iTRAQ-mass spectrometric identification of proteins differentially associated with the poly(C) element or its mutant, nucleolin was determined to be a cofactor of hnRNP K for FLIP activation. Furthermore, FLIP was highly expressed in tumor cells, and this high-level expression was significantly correlated with high-level hnRNP K expression (P=0.002) and poor overall survival (P=0.015) as examined in 67 NPC tissues. A multivariate analysis confirmed that FLIP was an independent prognostic factor for NPC. Taken together, these findings indicate that FLIP expression is transcriptionally regulated by hnRNP K and nucleolin, and may be a potential prognostic and therapeutic marker for NPC.

Presence of Epstein-Barr virus latent membrane protein 1 gene in the nasopharyngeal swabs from patients with nasopharyngeal carcinoma.

BACKGROUND: Nasopharyngeal carcinoma (NPC) is the most common head and neck malignancy in southeastern China and Taiwan. Early detection of the local disease followed immediately by proper treatment is essential to increase the cure and survival rates. Because every NPC tumor cell carries Epstein-Barr Virus (EBV) genomes, detection of EBV genomic DNA such as latent membrane protein 1 gene (LMP1) might indicate the presence of NPC. We developed a simple and noninvasive technique of nasopharyngeal swabbing to acquire nasopharyngeal cells for detecting the presence of EBV genome. The aim of this study was to investigate the feasibility and reliability of this technique. METHODS: We collected nasopharyngeal cells by means of a nasopharyngeal swabbing technique and detected the presence of EBV LMP1 with polymerase chain reaction (PCR). Thirty-eight swab specimens were obtained from patients with NPC who were newly diagnosed or were just beginning radiotherapy. Two groups of control subjects were recruited, including 20 patients with other head and neck cancers and eight family members of the NPC patients. An additional group of 65 NPC patients were enrolled in the course of regular follow-up after definitive radiotherapy. RESULTS: All of the samples yielded sufficient DNA for PCR amplification. Thirty-six of 38 NPC swab samples were positive for EBV LMP1, and all the control subjects had swab sample results negative for EBV. All five patients with suspected local recurrence exhibited positive EBV test results. CONCLUSIONS: Demonstration of EBV LMP1 in the nasopharyngeal swab specimens detected NPC with a sensitivity of 94.7% and specificity of 100%. This study confirms the reliability and feasibility of nasopharyngeal swab in the predicting and screening of NPC.

Differentiation of recurrent nasopharyngeal carcinoma and skull base osteoradionecrosis by Epstein-Barr virus-derived latent membrane protein-1 gene.

OBJECTIVES: In patients with nasopharyngeal carcinoma (NPC), the differentiation between recurrent primary cancer and osteoradionecrosis (ORN) is clinically difficult. Epstein-Barr virus (EBV)-derived latent membrane protein-1 (LMP-1) has been demonstrated to be highly associated with NPC. The objective of this study is to define the role of the LMP-1 gene in the differential diagnosis of recurrent NPC and ORN. STUDY DESIGN: Prospective. METHODS: From July 1998 to June 2000, 15 postirradiated patients with NPC who were initially diagnosed to have skull base ORN underwent endoscopic sequestrectomy. The sequestra were examined for the presence of the LMP-1 gene and cancer. RESULTS: Two of 15 patients had recurrent cancer and only these two patients demonstrated a positive LMP-1 gene in their surgically removed sequestra. The presence of the LMP-1 gene in the sequestrum coincided with biopsy-proven local recurrence. CONCLUSIONS: The LMP-1 gene is a potential marker to differentiate between recurrent NPC and ORN. The presence of the LMP-1 gene in patients with ORN may indicate local recurrence.

Effective relief of obstructive jaundice in a patient with nonresectable icteric-type hepatocellular carcinoma by external beam radiation therapy: case report.

We report on a 62-year-old woman with nonresectable icteric-type hepatocellular carcinoma who developed obstructive jaundice due to tumor thrombi in the common hepatic duct. External beam radiation therapy with total dose of 38 Gy was given in 10 fractions within 4 weeks. The serum bilirubin level progressively decreased from 30.0 to 1.7 mg/dl with a concomitant reduction of tumor size in the 2 months following radiotherapy. Serum alpha-fetoprotein level decreased from greater than 10,000 to 6540 ng/ml after radiotherapy but increased again due to new growth of tumors. The patient was subsequently treated by transcatheter arterial chemoembolization and was still alive 8 months after the diagnosis of nonresectable icteric-type hepatocellular carcinoma. This result suggests that external beam radiation therapy may be beneficial in some patients with nonresectable icteric-type hepatocellular carcinoma. When combined with other conventional therapies, radiation therapy may play an important role in the treatment of hepatocellular carcinoma.

Salivary gland type nasopharyngeal carcinoma: a histologic, immunohistochemical, and Epstein-Barr virus study of 15 cases including a psammomatous mucoepidermoid carcinoma.

Salivary gland type nasopharyngeal carcinomas (NPCs) are rare and not well characterized. Fifteen NPCs with adenocarcinomatous differentiation were studied for their histologic types, immunohistochemical features, and association with Epstein-Barr virus (EBV) by EBER in-situ hybridization (ISH) and by polymerase chain reaction (PCR) to detect latent membrane protein-1 (LMP-1) gene with formalin-fixed, paraffin-embedded tissues. Two cases of conventional NPC were included for comparison. The prevalence rate of salivary gland type NPCs was 1.3% of the total NPCs in this series. The patients consisted of 11 men and 4 women with ages ranging from 15 to 74 years (median, 50 yrs). Mucoepidermoid carcinoma was the most common type (53%) and an unusual psammomatous variant was found. Others were adenoid cystic carcinomas and various adenocarcinomas, including a papillary adenocarcinoma. A composite tumor of adenocarcinoma and undifferentiated carcinoma was also observed. The tumors were positive for AE1 and CK19 and generally negative for AE3 and CK20. Most cases were positive for epithelial membrane antigen and CA 19-9 with sporadic expression of carcinoembryonic antigen (CEA) and S-100 protein. Conventional NPC differed only in consistent immunonegativity for CA19-9 and CEA. EBV was detected by EBER ISH in 9 of 15 cases (60%) and by PCR of the LMP-1 gene in 10 of 15 cases (67%). Six of 10 LMP-1 gene-positive cases (60%) had a specific deletion of 30-base pairs (bp) of the LMP-1 gene. The result also supports the possible importance of a 30-bp deletion in conferring the oncogenecity of the LMP-1 gene. The prognosis of this series of salivary gland type NPCs was poor. Six of 13 patients with follow-up information already died of the disease with a median survival of only 1 year.

Endoscopic management of skull base osteoradionecrosis.

OBJECTIVE: Osteoradionecrosis is one of the most serious complications in radiotherapy of nasopharyngeal carcinoma. We describe a new endoscopic approach to resolve resultant skull base osteoradionecrosis. The objective of this study is to evaluate the efficacy of endoscopic management of skull base osteoradionecrosis. STUDY DESIGN: A prospective study of the outcome of endoscopic management for patients with skull base osteoradionecrosis. METHODS: Between 1994 and 1998 six patients who had irradiation previously for nasopharyngeal carcinoma had skull base osteoradionecrosis. A sinoscopic approach was applied for diagnosis and sequestrectomy. This diagnosis was based on the criterion of exposed necrotic bone after removing all crust in the nasopharynx and further confirmed on pathological examination after sequestrectomy. Effective cure was defined as intact mucosal coverage without any ulcer or exposed necrotic bone observed in the nasopharynx and the absence of antecedent accompanying symptoms after management. RESULTS: Six patients (10%) were symptom free. Five (83.3%) patients had effective cure. There was no surgical morbidity or mortality. CONCLUSION: Endoscopic sequestrectomy is a justified approach to skull base osteoradionecrosis.

Causes of interruption of radiotherapy in nasopharyngeal carcinoma patients in Taiwan.

BACKGROUND: Nasopharyngeal cancer (NPC) is now curable with early diagnosis and radiotherapy treatment. In the past several decades, few studies have investigated why some patients fail to complete the recommended full course of radiotherapy. METHODS: A total of 3273 nasopharyngeal carcinoma patients were treated at the Radiation Oncology Department of Linkou Chang Gung Memorial Hospital in a span of 18 years from 1979 to 1996. Among these patients, 276 did not complete the full course of treatment of radiation therapy. The medical records of these patients were reviewed to determine the factors contributing to treatment interruption. RESULTS: Of the 276 patients whose treatment was interrupted, 120 (43.5%) were unable to endure the acute side effects of radiation therapy and were afraid of the possible complications resulting from the treatment; 57 (20.7%) had doubts about the diagnosis or had the subjective perception that the treatment offered would be ineffective in view of the severity of their disease; 50 (18.1%) resorted to folk prescriptions; 17 (6.2%) were faced with socioeconomic problems; 15 (5.4%) sought treatment at another hospital owing to transport considerations; 10 (3.6%) stopped radiation therapy and switched to chemotherapy for palliative management; seven (2.5%) resorted to praying, god worshipping and taking incense powder and magic elixirs because their families were against any established therapy. CONCLUSIONS: The acute side effects and complications caused by radiation therapy were the major factors influencing patients' decisions to discontinue treatment. This finding suggests that more attention should be paid to providing care with regard to the acute side effects of radiotherapy and to reinforcing pretreatment education.

Second malignant tumors in patients with nasopharyngeal carcinoma and their association with Epstein-Barr virus.

Since previous published studies about second malignant tumors (SMTs) in nasopharyngeal carcinoma (NPC) patients usually included a limited sample size and did not attain consistent results, we conducted a large retrospective study in a cohort of 1,549 patients to assess the risk of SMT in NPC patients following radiotherapy (RT) in Taiwan. The follow-up period ranged from 2 to 16 years, with a median of 7 years. Thirty-nine patients developed SMTs during the 7,145 person-year follow-up [standardized incidence ratio (SIR): 2. 8; 95% confidence interval (CI): 2.0 to 3.9]. Increased risks of developing SMTs were observed for head and neck (H/N) cancer (SIR: 16.5; 95% CI: 10.0 to 26.8), gastric cancer (SIR: 5.5; 95% CI: 2.2 to 11.4) and leukemia (SIR: 9; 95% CI: 1.9 to 26.3). Paraffin-embedded specimens of secondary H/N cancer (11), secondary gastric cancer (6) and their corresponding NPC specimens were examined by EBER in situ hybridization to assess the association between Epstein-Barr virus (EBV) and these SMTs. Twenty-six primary H/N and 5 gastric cancer specimens were chosen as the control groups. In H/N cancer, EBV was detected in 3.8% of the primary cancers and 9.1% of the secondary cancers. All the positive specimens resulted from hypopharyngeal cancer. Of the secondary gastric cancers, only 1 case (16.6%) was associated with EBV. None of the primary gastric cancers was associated with EBV. Our results indicate an increased risk of developing SMTs, with a preference for head and neck cancer, gastric cancer and leukemia, in NPC patients after RT in Taiwan. Only a small proportion of the secondary H/N and gastric cancers was associated with EBV.

Locally recurrent nasopharyngeal carcinoma.

PURPOSE: To assess the outcome of and determine prognostic factors for locally recurrent nasopharyngeal carcinoma (NPC) in patients treated with a second course of radiotherapy (RT). MATERIALS AND METHODS: From 1982 to 1995, 186 NPC patients, who had initially been treated in the Department of Radiation Oncology, Chang Gung Memorial Hospital-Linkou, developed local recurrence in the nasopharynx and were re-treated with RT (>/=20 Gy). The time from the initial RT to re-treatment ranged from 8 to 136 months (median: 23 months). All patients were treated with external RT and conformal radiotherapy was used in 35 patients after 1993. Fifteen received radiosurgery as a boost treatment. The RT dose at the nasopharyngeal tumor area ranged from 20 to 67.2 Gy (median 50 Gy). Eighty-two patients received one to eight courses of cisplatin-based chemotherapy in addition to RT. RESULTS: The 1-, 3- and 5-year survival was 54.9, 22. 1 and 12.4%, respectively. Patients whose tumor relapsed later than 2 years after the first treatment had a better survival than those with earlier relapse (3-year survival: 30.1 vs. 10.8%; P=0.015), but the difference became insignificant in patients who received >/=50 Gy. Patients without evidence of intracranial invasion or cranial nerve palsy had better survival than those with such lesions (3-year survival: 30.9 vs. 3.7%; P=0.006). A re-treatment dose >/=50 Gy yielded better survival (3-year survival: 22.8 vs. 18.5%; P=0.003). Addition use of radiosurgery may improve survival. The use of chemotherapy did not improve survival. Conformal radiotherapy resulted in significantly fewer severe complications than conventional RT. CONCLUSIONS: A repeat course of RT for locally recurrent NPC successfully prolongs survival in a significant number of patients. Intracranial invasion and/or cranial nerve palsy and re-treatment dose affect the prognosis, with a dose of >/=50 Gy significantly improving survival. Radiosurgery boost may also improve survival. Our preliminary data indicates that conformal radiotherapy may decrease the severity of radiation-induced complications. However; longer follow-up and larger sample size is necessary to document the findings.

Advanced bilateral retinoblastoma treated conservatively with lens sparing external beam radiation therapy: report of three cases.

From 1995 through 1998, 3 children with bilateral advanced retinoblastoma were treated primarily with external beam radiation therapy; 6 eyes were irradiated with a lens sparing technique, doses varied from 5500 to 5700 cGy, and follow-up period ranged from 14 to 36 months. Recurrent tumors were found in 3 eyes, and a new growing tumor in one eye. Three eyes underwent enucleation eventually; one eye refused enucleation and finally developed optic nerve extension. The overall ocular cure rate was 2/6 (33.3%). One eye sustained visual acuity of 20/30, the other eye retained some peripheral vision; both eyes were blind in one patient. There were no deaths, metastasis, or secondary malignant tumors in our study. Advanced bilateral retinoblastoma with simultaneous radiation therapy instead of bilateral enucleation does not increase the risk of death, and more children will enjoy the benefits of retaining some vision in the affected eye through the use of this conservative therapeutic regimen.

A quick method to extract DNA from paraffin-embedded tissues.

BACKGROUND: The amplification power of the polymerase chain reaction (PCR) technique has had great impact in molecular analysis, and DNA extraction is a common requirement in retrospective studies utilizing PCR as a tool. Conventional methods used in deparaffinization, harvesting and purification of DNA from paraffin-embedded tissue are time consuming and cause a significant loss in the yield of DNA. METHODS: We utilized heating-melting-cooling removal of paraffin, digestion of the sample with proteinase K and purification of the extracted DNA by a microconcentrator. The products, after PCR amplification of the p53 gene exon 8, were used to make a comparison between our method and the conventional xylene-phenol-choloform method. RESULTS: The amplified products from our method were superior to that of the conventional method. CONCLUSION: The method we propose has a better recovery of DNA and is more time efficient.

Kadish stage C olfactory neuroblastoma successfully treated by chemoradiotherapy: report of two cases.

Olfactory neuroblastoma is an uncommon tumor. It is usually diagnosed at advanced stages. Most of the patients have an indolent clinical course with slow progression, late recurrence and relative infrequency of distant metastasis. Because of the rarity and lack of a randomized clinical trial of patients with olfactory neuroblastoma, there is no standard treatment for the disease. The survival period has increased as treatments have been improved since 1980. Conventional treatments mainly consist of surgery and/or radiotherapy. Chemotherapy was only administered to a few patients; however, it achieved good response. More clinical experience is needed to improve the treatment strategy in order to reduce the possibility of disease recurrence, and also for rescue therapy. We present 2 patients with Kadish C tumors treated using chemotherapy followed by radiotherapy. Both patients demonstrated rapid and excellent response to induction chemotherapy, and have been free of disease for more than 5 years and 2 years after treatment, respectively.

Results of external beam radiotherapy in patients with well differentiated thyroid carcinoma.

Surgical, thyroid hormone and radioactive 131I therapy are the standard curative treatments for well differentiated thyroid cancer. However, for residual, recurrent and nodal involvement of well differentiated thyroid cancer, external radiotherapy may be important in preventing distant metastases. The postoperative treatment of well differentiated human thyroid cancer with external radiotherapy is controversial. We retrospectively reviewed the records of 699 patients with papillary or follicular thyroid cancer, of whom 72 received external radiotherapy treatment after surgery. Thirty-two of these patients were at clinical stage 2 or 3 at the time of diagnosis while 172 patients at clinical stages 2 or 3 did not receive external radiotherapy after surgery. The patients who received external radiotherapy were older than those who did not (42.9 +/- 14.5 vs. 38.6 +/- 15.3), although this was not statistically significant. There were no significant differences in clinical parameters including surgical methods employed, histopathological types of cancer, follow-up stages, postoperative thyroglobulin levels, tumor size, accumulated 131I doses and survival rates between the two groups. To clarify the effect of external radiotherapy in patients with local invasion, we compared the survival rates of the patients with clinical stage 3 in the two groups and again no significant difference was found. During the follow-up period, 21 (28.4%) of the 72 patients who received external radiotherapy died of thyroid carcinoma. In our limited period of study, external radiotherapy did not improve the survival rate of patients with well differentiated thyroid cancer, though it appeared to cause temporary tumor regression.

Abrogation of p53 function by transfection of HPV16 E6 gene enhances the resistance of human diploid fibroblasts to ionizing radiation.

In order to examine the role of p53 expression on the sensitivity of cells to radiation-induced reproductive failure, we examined the radiosensitivity of a human diploid fibroblast cell strain (AG1521) before and after transfection with the E6 or E6/E7 genes of human papillomavirus 16 (HPV16)3. HPV E6 binds to p53, promoting its degradation and abrogating wild-type p53 function. AG1521 cells transfected with either E6 or E6/E7 showed no radiation induction of either p53 or WAF1/Cip1. The radioresistance of these cells were significantly increased; the D0 of the survival curves rose from 130 +/- 4 cGy for wild type (neo-transfected) cells to 178-192 cGy for three subclones transfected with E6 alone, and 151-218 cGy for eight subclones transfected with E6/E7. The change in radiosensitivity took place before the process of cellular immortalization and transformation produced by transfection with these genes. Thus, the effect on radiosensitivity appears to be an early effect of the loss of p53 function in non-transformed cells, perhaps related to the loss of the G1 checkpoint and of the capacity for programmed death amongst radiation damaged cells.

Altered p53 status correlates with differences in sensitivity to radiation-induced mutation and apoptosis in two closely related human lymphoblast lines.

Previous work identified TK6 and WTK1 as human lymphoblast cell lines from one donor that have different capacities to catalyze recombination and that vary significantly in their response to ionizing radiation. WTK1 cells are more resistant to the toxic effects of X-rays yet more sensitive to induced mutation. We demonstrate here that although both cell lines contain equal levels of p53 mRNA, baseline protein levels are 4 times higher in WTK1. Irradiation leads to higher levels of p53 protein in both lines but to a greater extent in TK6. TK6 contains a wild-type p53 sequence, while WTK1 has a homozygous mutation in codon 237 of exon 7. We also observed a significant difference in the kinetics but not the overall degree of apoptosis induced by X-rays in these cells; apoptotic death is delayed for 3 days in WTK1. We hypothesize that this p53 mutation is responsible for the difference in apoptosis as well as for the differences in mutability and mutational spectra reported previously.

Effect of restoration of retinoblastoma gene function on the radiosensitivity of cells of human tumor cell lines.

To assess the role of expression of the retinoblastoma (RB) gene on the sensitivity of cells to the cytotoxic effects of ionizing radiation, we transfected a normal RB gene into cells of RB+ and RB- osteosarcoma cell lines and an RB- prostate carcinoma line and studied the radiosensitivity of the cells before and after transfection. Four transfected clones were isolated from the two RB- tumor cell lines that expressed the product of the transfected normal RB gene and contained no mutations in the pocket and C-terminal regions by sequencing. A small increase in radiosensitivity was observed in cell lines transfected with the pDOL plasmid vector alone, containing the neo gene and a long terminal repeat (LTR) promoter. However, no significant change in radiosensitivity occurred in transfected cells expressing the normal RB gene compared to controls transfected with an RB- plasmid. Based on this and other information, we conclude that RB gene function is not involved in the response of these human tumor cells to the cytotoxic effects of radiation.

Effect of dose rate on the survival of irradiated human skin fibroblasts.

The survival of cells in density-inhibited, confluent cultures maintained at 37 degrees C was examined following exposure to 137Cs gamma rays at low dose rates (0.023 or 0.153 Gy/h) or to 60Co gamma rays at a single high dose rate (0.70-0.75 Gy/min). Cells from an ataxia telangiectasia (AT) homozygote showed no dose-rate effect, whereas a three- to fivefold increase in D0 was observed for all other cell strains exposed at low dose rates. The magnitude of the dose-rate effect did not differ significantly among cells from persons with hereditary retinoblastoma, basal cell nevus syndrome, or AT-heterozygote compared with normal cell strains, and was not related to the size of the shoulder (extrapolation number) of the survival curve. Furthermore, no differences in the capacity for the repair of potentially lethal damage during confluent holding were observed among these latter cell strains.