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Biomedical subjects

D K Chan

Publications and source records attributed to D K Chan.

At least 37 records · Page 2Linked to original sources
PubMed1997

Williams syndrome--the Singapore General Hospital experience.

Williams syndrome first described in 1961 is generally characterised by mental deficiency, gregarious personality, unusual "elfin" facies, supravalvular aortic stenosis and idiopathic infantile hypercalcaemia. Patients with Williams syndrome show a hemizygous submicroscopic deletion of 7q11.23 detectable by fluorescent in-situ hybridisation (FISH). The deleted portion of the chromosome corresponds to the Elastin gene. We report 3 girls with characteristics of Williams syndrome in whom the diagnosis was confirmed by demonstration of the hemizygous deletion of 7q11.23 in the karyotype by FISH. These patients, aged 6, 7 and 10 years, showed the characteristic facies and gregarious personalities. Some developmental delay with mild mental deficiency and dysmorphic facies were prominent features in the initial presentation. Cardiac lesions found in these patients were small patent ductus arteriosus which closed, pulmonary valvular stenosis and mitral valve prolapse associated with mitral regurgitation respectively. Hypercalcaemia was not documented in these patients. Learning difficulty was a major issue and all patients required special schooling. Chromosome analyses done on peripheral blood were found to be normal in all patients. FISH using the Elastin Williams Syndrome Chromosome Region (WSCR) probes (oncor) showed the hemizygous deletion of 7q11.23. Diagnosis of Williams syndrome can now be confidently confirmed with the help of FISH.

Child↗
PubMed1997

Usefulness of C-reactive protein in the diagnosis of neonatal sepsis.

AIM: Early diagnosis of sepsis in the neonate is often difficult because symptoms and signs are usually non-specific. A study was conducted to evaluate C-reactive protein (CRP) as a screening tool for neonatal sepsis among very low birth weight (VLBW) infants. METHODS: The study population consisted of 70 VLBW infants suspected of sepsis. Sepsis was diagnosed from positive cultures of blood, cerebro-spinal fluid or bone/joint aspirate in the presence of signs. Positive cultures were the "gold standard" against which the performance of CRP > or = 1.0 mg/dL, abnormal white cell counts (WCC), absolute neutrophil (ANC) and platelet counts were compared. RESULTS: Of 152 septic screens, 30 (20%) had positive cultures. From analysis of the receiver operating characteristic (ROC) curve, CRP > or = 0.7 mg/dL rather than CRP > or = 1.0 mg/dL appeared a better cut-off for screening. The sensitivity, specificity, positive and negative predictive values of CRP > or = 0.7 mg/dL were 56%, 72%, 71% and 57% respectively. Only abnormal platelet counts had similar efficiency as CRP. Abnormal WCC had the lowest sensitivity and positive predictive value while abnormal ANC had the lowest specificity and negative predictive value among them. CONCLUSION: CRP assay using laser nephelometry is a valuable adjunct in screening for neonatal sepsis, complementing clinical decision-making.

Biomarkers↗
PubMed1996

Staging of nasopharyngeal carcinoma: evaluation of N-staging by Ho and UICC/AJCC systems. Union Internationale Contre le Cancer. American Joint Committee for Cancer.

To evaluate the prognostic accuracy of N-staging by Ho's and the UICC/AJCC systems, 5020 patients with undifferentiated or poorly differentiated squamous cell carcinoma of the nasopharynx treated at the Queen Elizabeth Hospital, Hong Kong in the period 1976-1985 were analysed retrospectively. They were initially staged with Ho's system, but detailed records of nodal involvement allowed accurate retrospective restaging with the UICC/ AJCC (1988) system. Staging assessment depended almost entirely on physical examination; only 14% of patients had additional investigations with computed tomography. To evaluate the independent significance of different nodal parameters, T-stage adjusted analyses of the 4730 patients presenting without distant metastases were performed. Both N-staging systems showed a strongly significant overall correlation with distant failures and cancer-specific deaths. A significant trend was also shown for nodal failures in node-positive patients. Ho's system was superior in predicting distant failures, while the UICC/AJCC system was superior for nodal failures. However, even with due adjustment for level, the independent significance of nodal size, laterality and fixity could be demonstrated. After adjustment for UICC/AJCC N-stage, both level and fixity were also significant. Furthermore, when adjusted for all other meaningful parameters, there were no significant differences between ipsilateral and contralateral involvement, upper and mid-level extent, and nodal size < or = 3 cm or > 3- < or = 6 cm. N-staging can be further optimized by a newly proposed system incorporating fixity (movable versus fixed), level (upper-mid versus lower), size (greatest diameter < or = 6 cm versus > 6 cm), and laterality (unilateral versus bilateral) as staging criteria.

Adolescent↗
PubMed1996

Measuring the adoption of consistent use of condoms using the stages of change model. AIDS Community Demonstration Projects.

The stages of behavior change model has been used to understand a variety of health behaviors. Since consistent condom use has been promoted as a risk-reduction behavior for prevention of human immunodeficiency virus (HIV) infection, an algorithm for staging the adoption of consistent condom use during vaginal sex was empirically developed using three considerations: HIV prevention efficacy, analogy with work on staging other health-related behaviors, and condom use data from groups at high risk for HIV infection. This algorithm suggests that the adoption of consistent condom use among persons at high risk can be meaningfully measured with the model. However, variations in the algorithm details affect both the interpretation of stages and apportionment of persons across stages.

Acquired Immunodeficiency Syndrome↗
PubMed1995

Effect of time, dose and fractionation on local control of nasopharyngeal carcinoma.

To study the effect of radiation factors on local control of nasopharyngeal carcinoma, 1008 patients with similarly staged T1N03M0 disease (Ho's classification) were retrospectively analyzed. All patients were treated by megavoltage irradiation alone using the same technique. Four different fractionation schedules had been used sequentially during 1976-1985: with total dose ranging from 45.6 to 60 Gy and fractional dose from 2.5 to 4.2 Gy. The median overall time was 39 days (range = 38-75 days). Both for the whole series and 763 patients with nodal control, total dose was the most important radiation factor. The hazard of local failure decreased by 9% per additional Gy (p < 0.01). Biological equivalents expressed in terms of Biologically Effective Dose or Nominal Standard Dose also showed strong correlation. Fractional dose had no significant impact. The effect of overall treatment time was insignificant for the whole series, but almost reached statistical significance for those with nodal control (p = 0.06). Further study is required for elucidation, as 85% of patients completed treatment within a very narrow range (38-42 days), and the possible hazard is clinically too significant to be ignored.

Actuarial Analysis↗
PubMed1994

T1 nasopharyngeal carcinoma: the effect of waiting time on tumor control.

PURPOSE: To study the effect of unperturbed tumor growth on the control of nasopharyngeal carcinoma. METHODS AND MATERIALS: This is a retrospective analysis of 290 patients with T1N0-3M0 disease (Ho's classification) treated by the same technique and dose schedule to the nasopharyngeal region. The median interval from diagnosis to commencement of irradiation was 26 days (range: 8-68 days). Cox proportional hazards analyses were performed to study the independent effect of waiting time on the probability of failure at various sites. Actuarial failure-free survival of patients with delay < 22 days, 22-28 days and > 28 days were also compared to illustrate the clinical observation. RESULTS: Both tests showed that waiting time had no significant impact on local failure: The N-stage stratified hazard ratio was 0.985 per day, and the 10-year local failure-free survival for the three groups was 76%, 80%, and 82%, respectively. A similar result was obtained for nodal control in patients with our scheduled neck irradiation. Although the p value of all tests failed to reach statistical significance, the N-stage stratified hazard ratio for distant failure was 1.020 per day, and the corresponding metastasis-free survival in patients with N2-3 disease was 70%, 65%, and 52%, respectively. For node-negative patients without elective neck irradiation, the hazard ratio was 1.019 per day, with the corresponding regional failure-free rates at 57%, 62%, and 33%, respectively. CONCLUSION: Delay in initiation of treatment to the primary target (within the range observed) did not affect the control rate at irradiated sites, but there was a trend (though statistically insignificant) towards increase in failures at untreated sites that were clinically too serious to be ignored.

Adult↗
PubMed1993

Retrospective analysis of patients with nasopharyngeal carcinoma treated during 1976-1985: survival after local recurrence.

PURPOSE: To study the value of re-irradiation, the overall survival and pattern of failures for patients with nasopharyngeal recurrence. METHODS AND MATERIALS: All the 891 patients with local recurrence following radiotherapy for nasopharyngeal carcinoma during 1976-1981 were retrospectively analyzed. Only 70% of them had local failure alone at the time of detection, and the T-stage distribution (by Ho's system) was 31% rT1, 16% rT2, 51% rT3, and 1% rT?. Seven hundred and six (79%) patients had been re-irradiated with various techniques and doses. Among those who failed, 50 had further irradiation. RESULTS: The overall 5- and 10-year actuarial cancer-specific survival rates were 14% and 9%, respectively. Patients with rT3 disease had the worst prognosis. Successful local salvage was achieved in 32% of those re-irradiated (26% of the whole series). The highest control rate was achieved by those treated with external radiotherapy to 60 Gy (equivalent) or above. Only 8/50 patients responded to the third course of radiotherapy. The cumulative incidence of late post-re-irradiation sequelae was 24%, and the treatment mortality rate 1.8%. Besides local failure, 54% had regional relapse and/or distant metastasis. Thus, only 16% of recurrent patients were totally disease-free at final assessment. CONCLUSION: The overall prognosis for patients with nasopharyngeal recurrence was grave. High dose re-irradiation could achieve successful local salvage in a substantial number of patients with early recurrence, but late complications did occur. Furthermore, high incidence of failure at other sites was observed.

Adolescent↗
PubMed1993

Nasopharyngeal carcinoma: local control by megavoltage irradiation.

This is a retrospective analysis of the long-term local control in 4128 patients with non-disseminated nasopharyngeal carcinoma treated solely by megavoltage irradiation during the years 1976-1985. The T-stage distribution according to Ho's classification was T1 37%, T2 14% and T3 49%. Different fractionation schedules had been employed at different periods, and the median dose to the primary target was equivalent to 65 Gy by time dose fractionation calculation. In 8% (344) of patients the tumour failed to regress completely after the basic course, but 89% (148/167) of those suitable for salvage with additional irradiation eventually attained complete local remission. The cumulative incidence of local failure was 24% (5% persistence, 19% recurrence). The 10-year actuarial local failure-free survival was 67%. While patients with T2 and T3a tumours achieved local control comparable to T1, those with T3c-d had the poorest control (with highest incidence of persistence and advanced recurrence). T-stage adjusted analyses suggested a significant trend of dose-response: the odds ratios for local failure were 1.16 and 1.86, respectively, when patients given 60-63 Gy and 55-59 Gy were compared with those given 64 Gy or above (p value = 0.0018). Patients treated during 1981-1985 achieved higher local failure-free survival than those treated during 1976-1980 (75% versus 70% at 5 years, p value = 0.0013). The possible attributes are studied, and ways for future optimization of treatment discussed.

Adolescent↗
PubMed1993

Definitive radiotherapy for carcinoma of the oral tongue.

This is a retrospective analysis of 117 patients with carcinoma of the oral tongue treated by definitive radiotherapy during 1979-1990. Sixty-seven per cent of patients presented with T1-2 disease. Their cumulative incidence of local failure was 10% (5/50) for those suitable for treatment with implant alone, 81% (13/16) for those treated with external irradiation alone and 67% (8/12) after combined treatment. These differences could largely be explained by selection factors as smaller and less bulky tumours generally were selected for implant treatment. Among the patients who achieved local control, there was no incidence of regional relapse (0/9) for those with elective neck irradiation, but 33% (15/46) for those without. This incidence correlated with size of primary tumour. Radiotherapy achieved effective local control in 13% (5/39) of T3-4 tumours, and regional control in 43% (12/28) of N1-3 cases. Only 32% (24/76) of patients with local and/or regional recurrence were successfully salvaged. Ways of improving the treatment are discussed.

Adult↗
PubMed1992

Retrospective analysis of 5037 patients with nasopharyngeal carcinoma treated during 1976-1985: overall survival and patterns of failure.

This is a retrospective analysis of 5037 patients with squamous cell carcinoma of the nasopharynx treated during the years 1976-1985. The stage distribution according to Ho's classification was 9% Stage I, 13% II, 50% III, 22% IV, and 6% Stage V. Only 4488 (89%) patients had a full course of megavoltage radiation therapy. The median equivalent dose to the nasopharyngeal region was 65 Gy and cervical region in node-positive patients 53 Gy. Seventy percent (906/1290) of the node-negative patients had no prophylactic neck irradiation. The overall actuarial 10-year survival rate was 43%, and the corresponding failure-free survival 34%. Altogether, 4157 (83%) patients achieved complete remission lasting more than 6 months, but 53% (2205/4157) of them relapsed after a median interval of 1.4 years. The 10-year actuarial local, regional, and distant failure-free rates were 61%, 64%, and 59%, respectively. Thirty-eight percent (338/891) of all patients with local recurrence achieved second local remission. The local complete remission rate with aggressive re-irradiation alone was 47% (333/706). But 37% (124/338) of the responders recurred the second time. The incidence of distant failure correlated significantly with both the N-stage and the T-stage, with the highest (57%) occurring in patients with N3 disease. The incidence of nodal relapse in node-negative patients was 11% (44/384) among those given prophylactic neck irradiation, but 40% (362/906) among those without. Therapeutic irradiation achieved a complete regional remission rate of 90% (306/339). However, despite successful salvage, these patients had a significantly higher distant failure rate than those without nodal relapse, even if they remained local-failure-free (21% vs 6%). Patients treated during 1981-1985 achieved significantly better treatment results than those treated during 1976-1980, especially in terms of the overall survival (57% vs 47% at 5-year), the overall failure-free survival (42% vs 35% at 5-year), and the local failure-free rate (70% vs 63% at 5-year). The possible contributing factors are discussed.

Adolescent↗
PubMed1992

Retrospective analysis of nasopharyngeal carcinoma treated during 1976-1985: late complications following megavoltage irradiation.

A retrospective analysis was undertaken of the late complications observed in 4527 patients with nasopharyngeal carcinoma treated by megavoltage radiotherapy during the years 1976-1985. Unconventional fractionation schedules were used because of serious resource limitations. The median equivalent doses were 65 Gy to the nasopharyngeal region and 53 Gy to the cervical region. 707 patients had reirradiation for local recurrences and 250 for regional relapses. The 10-year actuarial cancer-specific survival was 47%, and the corresponding all-complication-free and neurological-complication-free rates were 40% and 72%, respectively. Altogether, 1395 (31%) patients developed one or more late irradiation sequelae. The majority were mild soft-tissue damages, but 322 (7%) had significant functional disturbances, from which 62 (1%) died. Neurological damage that occurred in 450 (10%) patients constituted the major morbidity and accounted for all but three of the treatment mortalities. The cumulative incidence of the various complications is summarized, and the data recorded in the literature reviewed in order to give a proper perspective of the problem. Patients treated during 1981-1985 had a significantly higher actuarial encephalomyelopathy-free rate than those treated during 1976-1980, but the incidence-free rates for the other neurological complications remained unimproved, suggesting that the improvement could be mainly attributed to additional shielding for the brainstem rather than the reduction of dose from 3.8-4.2 Gy to 2.5 Gy per fraction.

Adolescent↗
PubMed1989

Noonan syndrome with spontaneous chylothorax at birth.

A female Chinese infant having the features of Noonan syndrome presented with acute respiratory distress at birth, secondary to a large spontaneous left-sided chylothorax. This condition must be recognized early in such infants, as prompt thoracentesis is life-saving.

Chromosome Aberrations↗