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Biomedical subjects

S Leung

Publications and source records attributed to S Leung.

At least 91 records · Page 5Linked to original sources
PubMed1991

The effect of embryo quality on subsequent pregnancy rates after in vitro fertilization.

OBJECTIVE: To determine if a simple morphological classification of embryos was predictive of subsequent pregnancy. DESIGN: Prospective case series. SETTING: University-based in vitro fertilization (IVF) program. PATIENTS, PARTICIPANTS: Consecutive embryo transfer (ET) cycles (n = 206). INTERVENTIONS: Embryos were classified into three grades: (1) equal-size blastomeres with no fragmentation; (2) unequal-size blastomeres; and (3) evidence of fragmentation. MAIN OUTCOME MEASURES: Embryo quality, age, indication for IVF, and stimulation protocol were evaluated for their effect on pregnancy rates (PR's). RESULTS: In cycles in which the best embryo transferred was grade 3, 2, or 1, the clinical PRs per ET were 0% (0/11 cycles), 12.8% (6/47 cycles, P less than 0.05), and 21.8% (32/148 cycles, P less than 0.05), respectively. When one, two, or three or more grade 1 embryos were replaced, the clinical PRs per ET were 15.6%, 16.3%, and 40% (P less than 0.05), respectively. Using logistic regression, embryo quality (P = 0.0011) and patient's age (P = 0.0044) were the only variables that affected PRs. CONCLUSION: The transfer of more than two good quality embryos had a positive effect, patient's age had a negative effect on PRs after IVF-ET.

Age Factors↗
PubMed1990

Interstitial iridium 192 for cutaneous carcinoma of the external nose.

Several implantation techniques useful for nasal skin carcinoma have been developed at the Henri Mondor Hospital in Créteil, France and are described in detail. Iridium 192 wires, 0.3 mm in diameter, are afterloaded into either supple plastic tubes or rigid needles implanted according to the rules of the Paris system. Dosimetry is performed by computer, based on either direct measurements of active lengths and spacing, orthogonal films or a tomogram oriented in the central plane of the implant. According to a recent review by the European Curietherapy Group of 468 implants, the optimal dose is 60 Gy. The overall failure rate was 2.6%. Indications for implantation and choice of technique, based on tumor size, site, and gross morphology are discussed.

Brachytherapy↗
PubMed1990

Perineal template techniques for interstitial implantation of gynecological cancers using the Paris system of dosimetry.

Since 1984, perineal template/needle techniques for interstitial implantation of gynecologic cancer-cervix, vagina, vulva-have been developed at the Peter MacCallum Cancer Institute. The Paris System of dosimetry has been used resulting in greater dose homogeneity, fewer needles and radioactive sources and considerable simplification and ease of implantation compared with comparable techniques developed in the United States. Principles and techniques of implantation are described in detail.

Adult↗
PubMed1989

Point mutational analysis of the human c-fos serum response factor binding site.

A series of point mutants were generated in the human c-fos dyad symmetry element (DSE), found within the c-fos serum response element, to study the sequence requirements for its interaction with the human HeLa cell serum response factor (SRF). Plasmids that contain base substitutions within a core CC(A/T)6GG motif in the center of the DSE did not compete, or competed very poorly, with the wild-type c-fos DSE for formation of a specific SRF-DSE complex in vitro. The CC(A/T)6GG motif is not sufficient for maximal binding of SRF, as several plasmids that contain base substitutions in the sequences flanking this core motif competed either poorer or better than the wild-type c-fos DSE for SRF binding. Evidence is presented that supports the idea that SRF binds in a symmetrical fashion. Results of in vivo transient expression assays in HeLa cells suggest that negative regulation of c-fos transcription observed in serum-deprived cells is mediated through SRF binding to the DSE.

Base Sequence↗
PubMed1989

Structure of the two promoters of the human lck gene: differential accumulation of two classes of lck transcripts in T cells.

The human T-cell- or lymphocyte-specific gene, lck, encodes a tyrosine kinase and is a member of the src family. In this report we demonstrate that there are two classes of human lck transcripts (types I and II), containing different 5'-untranslated regions, which are expressed from two distinct promoters. No apparent sequence similarity was observed between the 5'-flanking regions of the two promoters. The expression of lck in human T-cell leukemia and carcinoma cell lines and in human peripheral blood T lymphocytes was examined by S1 nuclease and primer extension mapping and by Northern (RNA) blot analysis of total cellular RNA. The following results were obtained. (i) Two RNA start sites in the downstream promoter were used to generate type I transcripts. (ii) The major human type I start site has not been described for the mouse. (iii) At least five RNA start sites in the upstream promoter were used to generate type II transcripts. (iv) In T cells and in two colon carcinoma cell lines, type II transcripts were present in higher amounts than type I transcripts. (v) In T cells treated with phytohemagglutinin, tetradecanoylphorbol acetate, and cyclosporin A, the modulation of lck expression was associated primarily with changes in levels of type II transcripts. The above results suggest that the two human lck promoters are utilized differentially and may be regulated independently during certain physiological states.

Base Sequence↗
PubMed1987

Update on low dose rate irradiation for cancers of the oropharynx--May 1986.

At the conclusion of our recently published article in this Journal on low dose rate irradiation in moderately extensive cancers of the oropharynx, we updated our results in May 1986. Here we report on an expanded group of 65 patients with a 2 year minimum follow-up; 32 patients were treated by low dose rate irradiation and 33 by conventional fractionation. Forty-four percent (14/32) low dose irradiation patients survived with NED vs 8/33 (24%) conventional fractionation patients. The highly significant differences in the level of local recurrences between patients treated by low dose rate irradiation, 5/32 (16%), compared with conventional fractionation, 20/33 (61%), highlights the enhanced efficacy of the low dose rate irradiation technique in the local cure of cancers of the oropharynx. This superior local control however is achieved at the cost of a number of necrosis, 5/32 (16%).

Humans↗
PubMed1987

The ratio of mid-arm circumference to occipital frontal circumference in Chinese babies: a marker of late gestation growth retardation.

The ratio of mid-arm circumference to occipital frontal circumference (MAC/OFC), an index of late gestation growth retardation, was determined in 175 healthy newborn term Chinese babies. The ratio of 0.31 (S.D., 0.02) was significantly higher than in recent data published for Asian, White and Black neonates: whether this is due to differences in measuring techniques or better intra-uterine nutrition remains to be seen. As an initial test of its potential usefulness this ratio was determined in 12 term Chinese babies who showed clinical signs of undernutrition. All but one had a ratio 2S.D. or more below the mean. The MAC/OFC ratio, with its ease of measurement, simplicity and cheapness, is a useful addition to existing methods for assessing late gestation nutritional status.

Arm↗
PubMed1986

Locoregional recurrences following radical external beam irradiation and interstitial implantation for operable breast cancer--a twenty three year experience.

Locoregional recurrences are reported in 493 consecutive with T1 T2 N0 N1 breast cancer patients who were treated with radical external beam irradiation and interstitial 192 Ir. implant between 1961 and 1979. Follow-up ranges from 5-23 years (mean 10 years) with 195 patients having 10-23 years follow up (mean 12 years). Tumorectomy was performed in 130/158 (88%) T1 and 73/335 (22%) T2 patients. There were 51 (10%) locoregional recurrences with 34 mammary, 14 combined mammary/axillary and 3 isolated axillary recurrences. The 10 year relapse rate was 20/195 (10%). The risk, timing and site of relapse varied according to TNM stage and tumorectomy. The risk was higher for T2 (42/335, 12.5%) than T1 (9/158, 5.5%) due to a larger number of recurrences occurring in the first 5 years (T2 32/335, 9.5% vs T1 4/158, 2.5%). Between 5-10 years, risk of relapse equalized to around 3% for both groups and only 1 relapse was seen after 10 years. Of the 48 mammary recurrences, 25 (52%) occurred in the implant volume, 7 (14%) occurred on the margin of the implant, 12 (25%) occurred at sites remote from the primary and in 4 (9%), the exact site could not be defined. 14/48 mammary recurrences were accompanied by axillary relapse, there were 3 isolated axillary recurrences and supraclavicular metastases accompanied axillary relapse in 3 cases. The overall risk, of axillary relapse was 3% (17/493) and there was significant correlation with initial N stage. Salvage surgery generally mastectomy and axillary dissection, was possible in 45/51 (90%) recurrences. 23/45 (50%) survive NED 0.2-9 years (mean 3 years) after salvage. 8/23 (35%) followed longer than 5 years after salvage survive NED. Our results have been compared with other series in the literature and changes in our current protocol are described.

Brachytherapy↗
PubMed1985

A comparison between low dose rate radiotherapy and conventionally fractionated irradiation in moderately extensive cancers of the oropharynx.

We report the comparative results for local tumor control between two groups of patients treated by radiotherapy fractionated in a conventional manner at normal high dose rate (29 patients with 2 years minimum follow-up and 24 patients with 3 years minimum follow-up) and by low dose rate radiotherapy (19 patients with 2 years minimum follow-up, 14 patients with 3 years minimum follow-up) with moderately extensive cancers of the oropharynx (T2b-T3a, 3-5 cm in diameter). At 2 and 3 years follow-up, the number of local recurrences in the patients treated with low dose rate radiotherapy is half (26 and 21%) that for those treated with conventionally fractionated radiation at normal high dose rates (52 and 54%). These results require more rigorous confirmation.

Carcinoma, Squamous Cell↗
PubMed1985

Comparative dosimetry between iridium wires and seed ribbons.

We have undertaken a computer study that explores the conditions under which seed ribbons may replace iridium 192 wires in the Paris System. Compared with continuous iridium 192 wires, seed ribbons demonstrate greater inhomogeneity and loss of flexibility, simplicity, and other advantages. Nonetheless, we have defined the conditions where seed ribbons may be used in the Paris System to give satisfactory dose distributions and acceptable levels of heterogeneity within any given implant volume. These conditions include seed length, spacing between seeds, number of seeds per ribbon, and geometric arrangement of ribbons.

Brachytherapy↗
PubMed1985

Intestinal complications of wide field abdominal irradiation for lymphoma.

We report bowel complications on a series of 32 patients treated with wide field abdominal irradiation for lymphoma between 1979 and 1983. Irradiation was preceded by chemotherapy in 30/32 patients. Fifteen of the 32 patients received total abdominal irradiation and 17/32 received upper hemi-abdominal irradiation to a dose of 20-25 Gy. A boost of 5-20 Gy to a reduced volume was added in 14/32. A special diet was prescribed from the start of irradiation. Immediate tolerance to irradiation was good in 94% of patients. Only five patients developed delayed bowel complications. Definite radiation-induced bowel changes were demonstrated in only two of these cases and other pathology was found to explain the symptomatology in the remaining three. Comparison with a previous series of 50 lymphoma patients treated with total abdominal irradiation to 30 Gy plus inverted Y boost to 10 Gy demonstrated a net improvement in the immediate tolerance and reduction in the incidence and gravity of delayed radiation-related bowel complications in the current series. The reasons for the improved early and late bowel tolerance (radiation dose and volume, etc.) as well as conditions which can mimic late radiation enteritis, will be discussed.

Abdominal Neoplasms↗
PubMed1985

Treatment of bladder tumors by iridium 192 implantation. The Créteil technique.

The technique and results of a treatment protocol for bladder cancer combining low dose pre-operative external beam irradiation followed by external iliac nodal dissection, limited partial cystectomy and curietherapy with iridium 192 are described. In 55 patients treated from 1971 to 1979, 37/45 (67%) are alive NED at 5 years--23/31 pT1, 10/14 pT2, 4/10 pT3--with 9/55 bladder recurrences at 5 years--7/31 pT1, 1/14 pT2, 1/10 pT3. Only two patients (total cystectomy) have not retained a functional bladder. These favorable results have been obtained in a carefully selected population; our indications for the technique being T1, T2, T3a tumors with a total surface area not exceeding 5 cm, not involving the bladder neck and unifocal or in some cases plurifocal, but closely grouped. The advantages and precise details of each stage of the technique will be described and compared with large series in which radium 226 is utilized and results of curietherapy will be compared with other modalities of treatment employed under similar circumstances for similar patient groups. We feel that curietherapy has certain advantages over other methods in the treatment of bladder cancer and that an afterloading technique employing iridium 192 wires permits the curietherapy to proceed under optimal conditions, allowing combination with partial cystectomy, optimal placement of sources, precise radiographic control and dosimetry, dose reduction in many cases, optimal conditions of radioprotection and widening of the indications for the technique.

Brachytherapy↗
PubMed1975

Galactolipid Synthesis in Vicia faba Leaves: I. Galactose, Glycerol, and Fatty Acid Labeling after CO(2) Feeding.

The galactose, glycerol, and fatty acids of mono- and digalactosyl diglycerides (MGDG and DGDG) have been separated and analyzed for (14)C activity after (14)CO(2) feeding of Vicia faba leaf discs. Fully expanded and developing leaves were analyzed at time intervals following feeding during continuous illumination. In addition, fully expanded leaves were analyzed after similar times in complete darkness. In all cases, (14)C was incorporated very rapidly into galactose, whereas glycerol and fatty acids were labeled much more slowly and over a longer period of time. The data are consistent with the galactosylation of a diglyceride to MGDG which is in turn galactosylated to DGDG. The data suggest that the formation of diglycerides suitable for galactosylation to MGDG is slow in comparison to the galactosylation process. It is also suggested that DGDG may be formed from more than one pool of MGDG. The complete analysis of the (14)C incorporation into galactose appears to represent the only satisfactory method of comparing galactolipid synthesis by (14)C incorporation. Estimates of comparative rates of synthesis of MGDG and DGDG have been made on this basis.

Journal Article↗
PubMed1975

Biosynthesis of digalactosyl diglyceride in Vicia faba leaves.

Developing and mature leaf tissue from Vicia faba plants were pulse-fed 14-CO2. The lipids were extracted at intervals after exposure to light, and the galactolipids monogalactosyl diglyceride (MGDG) and digalactosyl diglyceride (DGDG) were separated. After methylation and methanolysis, gas-liquid chromatography was used to separate the two galactose units of DGDG and the galactose of MGDG. The specific activities of the galactoses and the changes over the time period of the experiment were determined. The results support the view that DGDG is formed by galactosylation of MGDG. This does not take place by a rapid two-enzyme system reaction but more slowly in two phases: galactosylation of a pool of newly formed MGDG and a more random galactosylation of MGDG. There is no evidence of a high turnover of galactose in these lipids.

Carbon Dioxide↗