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S W Duffy

Publications and source records attributed to S W Duffy.

At least 91 records · Page 5Linked to original sources
PubMed1997

Markov models of breast tumor progression: some age-specific results.

Researchers have noted that mammographic screening has a reduced effect on breast cancer mortality in women in their forties compared to older women. Explanations for this include poorer sensitivity in younger women due to denser breast tissue, as well as more rapid tumor progression, giving a shorter mean sojourn time (the average duration of the preclinical screen-detectable period). To test these hypotheses, we developed a series of Markov-chain models to estimate tumor progression rates and sensitivity. Parameters were estimated using tumor data from the Swedish two-county trial of mammographic screening for breast cancer. The mean sojourn time was shorter in women aged 40-49 compared to women aged 50-59 and 60-69 (2.44, 3.70, and 4.17 years, respectively). Sensitivity was lower in the 40-49 age group compared to the two older groups (83%, 100%, and 100%, respectively). Thus, both rapid progression and poorer sensitivity are associated with the 40-49 age group. We also modeled tumor size, node status, and malignancy grade together with subsequent breast cancer mortality and found that, to achieve a reduction in mortality commensurate with that in women over 50, the interscreening interval for women in their forties should be less than two years. We conclude that Markov models and the use of tumor size, node status, and malignancy grade as surrogates for mortality can be useful in design and analysis of future studies of breast cancer screening.

Adult↗
PubMed1997

Factors related to cervicitis in Qashghaee nomadic women of southern Iran.

In a survey of reproductive habits and cervical pathology in 1015 women of the Qashghaee nomadic tribe of southern Iran, a high prevalence (80%) of cervicitis was observed. The effects of reproductive and other habits on risk of cervicitis were therefore assessed using proportional odds modelling. Increased risks of a higher degree of cervicitis were associated with middle to late age (p = 0.02), a history of delivery of children (p = 0.001), intercourse during menses (p = 0.03) and a history of ever giving birth in a maternity hospital (p = 0.02). A lower risk was associated with increased duration of marriage (p = 0.05). The increased risk observed for history of birth in maternity hospital may reflect a prior obstetric problem which predisposes to both cervicitis and seeking the specialist obstetric care provided in the maternity hospital. Results suggest an infectious agent which may be transmitted in childbirth.

Adult↗
PubMed1996

Tumour development, histology and grade of breast cancers: prognosis and progression.

Using 1,973 breast tumours from women aged 40-69 participating in the Swedish two-county trial of mammographic screening for breast cancer, we examined the effect of histological type on prognosis and sojourn time (the duration of the preclinical screen-detectable phase) by age. The hypothesis of dedifferentiation, according to which a cancer of mixed malignancy grade drifts towards grade 3 as the more poorly differentiated part of the tumour grows faster than the well-differentiated part, was also assessed. Ductal carcinoma in situ, invasive ductal carcinoma of grade 1, mucinous carcinoma and tubular carcinoma were all associated with good survival. Ductal carcinoma of grade 3 was associated with poor survival. Ductal carcinoma of grade 2, lobular and medullary carcinoma were associated with intermediate survival. These patterns were much the same in women aged 40-49 as in women aged 50-69. In women aged 40-49, sojourn time was estimated at about 2 years regardless of histological type. For women aged 50-69, there was a marked association of sojourn time with histological type, the shortest sojourn time being observed for lobular (2 years) and medullary (1.2 years) carcinoma, and the longest for ductal carcinoma grade 1 (7.7 years) and tubular carcinoma (7.1 years). There was strong evidence of a potential to dedifferentiation. A mover-stayer mixture of Markov chain models estimated that, in women aged 40-54, 91% of ductal tumours have the potential to dedifferentiate and, in women aged 55-69, 38% of ductal tumours have such a potential.

Adult↗
PubMed1996

Breast cancer in Singapore: trends in incidence 1968-1992.

BACKGROUND: Breast cancer is the most commonly occurring cancer among women in Singapore, a country which has experienced significant changes in lifestyle over the past three decades. The increase in incidence of the disease is a matter of some concern. METHODS: Data from the population-based Singapore Cancer Registry for 1968-1992 were used to determine time trends, inter-ethnic differences and the contributions of age, period and cohort effects to the incidence of the disease. RESULTS: Our results revealed an average annual increase of 3.6% over the 25-year period for all women, form 20.2 per 100,000 women in the period 1968-1972 to 38.8 per 100,000 in 1988-1992. There was a statistically significant difference between the three major ethnic groups, the rate of increase being highest in Malays (4.4%) and lowest in Indians (1.4%). The overall increase was attributable to a strong cohort effect that remained significant when adjusted for time period for Chinese women and for all ethnic groups combined. The risk was observed to increase in successive birth cohorts from the 1890s to 1960s. CONCLUSIONS: Our results suggest that breast cancer incidence rates are likely to continue to increase more sharply in the future as women born after the mid-20th century reach the high-risk age groups. They also suggest the pattern by which important aetiological factors for the disease in our population have exerted their effects, and provide support for the role of demographic and lifestyle changes as possible risk factors.

Adult↗
PubMed1996

Sojourn time, sensitivity and positive predictive value of mammography screening for breast cancer in women aged 40-49.

BACKGROUND: In mammographic screening for breast cancer in women aged 40-49, previous studies have found very low estimates of sensitivity and predictive value. Methods of estimation have, however, used primitive models with relatively strong assumptions and less than full use of the data. METHODS: Here we estimate the underlying preclinical incidence, mean sojourn time, sensitivity and positive predictive value by a variety of methods in a randomized trial of mammographic screening (The Swedish Two-County Trial) and a service screening programme (The Florence Programme, 1975-1986) in women aged 40-49 years. RESULTS: In the Two-County study, sensitivity estimates ranged from 72-83% and predictive value from 39-89%. In the Florence programme, sensitivity estimates ranged from 69-85% and predictive value was uniformly estimated as 100%. CONCLUSIONS: The methods involving more explicit modelling of the disease process and fewer assumptions tended to find higher estimates of predictive value in the Two-County study. The results suggest that previously poor sensitivity and predictive value estimates may have been overpessimistic.

Adult↗
PubMed1996

The value of the second view in screening mammography.

A prospective study of 33,734 women was undertaken during the prevalent round of the UK National Breast Screening Programme. The cancer detection rates and recall rates were compared between a one view and a two view technique. In one fifth of the women, only the single oblique view examination was read. To lose the bias that would have been introduced by the prior knowledge that a second view would be available, the radiologists reading the oblique view did not know whether or not a craniocaudal view would subsequently be available. Readings were available from two radiologists in each case. The cancer detection rate increased from 7.6 per thousand to 8.2 per thousand women screened, with 14 more cancers detected with the two view technique. This represents 6.5% of all screen detected cancers (95% CI 3.2-9.8). The recall rate was reduced from 8.8% to 6.6% by the second view (p < 0.001). There was a significantly higher biopsy rate in the two view group (10.6/1000 versus 8.6/1000) (p = 0.004). This higher biopsy rate is part of the price paid for the higher detection rate. The additional tumours included small invasive cancers. The National Health Service (NHS) cost of each additional cancer diagnosed was 4129 pounds and the NHS plus private cost was 2742 pounds. These findings have practical applications for the National Breast Screening Programme. There would be resource implications on routinely applying two view screening to the prevalent round, but even greater costs if applied to the incident screening round.

Breast Neoplasms↗
PubMed1995

Estimation of mean sojourn time in breast cancer screening using a Markov chain model of both entry to and exit from the preclinical detectable phase.

The sojourn time, time spent in the preclinical detectable phase (PCDP) for chronic diseases, for example, breast cancer, plays an important role in the design and assessment of screening programmes. Traditional methods to estimate it usually assume a uniform incidence rate of preclinical disease from a randomized control group or historical data. In this paper, a two-parameter Markov chain model is proposed and developed to explicitly estimate the preclinical incidence rate (lambda 1) and the rate of transition from preclinical to clinical state (lambda 2, equivalent to the inverse of mean sojourn time) without using control data. A new estimate of sensitivity is proposed, based on the estimated parameters of the Markov process. When this method is applied to the data from the Swedish two-county study of breast cancer screening in the age group 70-74, the estimate of MST is 2.3 with 95 per cent CI ranging from 2.1 to 2.5, which is close to the result based on the traditional method but the 95 per cent CI is narrower using the Markov model. The reason for the greater precision of the latter is the fuller use of all temporal data, since the continuous exact times to events are used in our method instead of grouping them as in the traditional method. Ongoing and future researches should extend this model to include, for example, the tumour size, nodal status and malignancy grade, along with methods of simultaneously estimating sensitivity and the transition rates in the Markov process.

Adult↗
PubMed1995

Efficacy of breast cancer screening by age. New results from the Swedish Two-County Trial.

BACKGROUND: Several studies have found a smaller effect of breast cancer screening on breast cancer mortality in women aged younger than 50 years compared with older women. Various possible reasons have been suggested for this, but none firmly is established. METHODS: The Swedish Two-County Study is a randomized trial of breast cancer screening of women aged 40-74 years, comprising with 133,065 women with a 13-year follow-up of 2467 cancers. The Breast Cancer Detection Demonstration Project (BCDDP) is a nonrandomized screening program in the United States, with a 14-year follow-up of 3778 cancers in women aged 40-74 years. The Swedish results by age were updated. The lesser effect of screening at ages 40-49 years was investigated in terms of sojourn time (the duration of the preclinical but detectable phase) size, lymph node status, and histologic type of the tumors diagnosed in the Swedish Study and their subsequent effect on survival using survival data from both studies. RESULTS: In the Swedish Trial, a 30% reduction in mortality associated with the invitation to screening of women aged 40-74 years was maintained after 13-years of follow-up. The reduction was 34% for women aged 50-74 years and 13% for women aged 40-49 years. Results indicated that the reduced effect on mortality for women aged 40-49 years was due to a differential effect of screening on the prognostic factors of tumor size, lymph node status, and histologic type. The mean sojourn times in the age groups 40-49 years, 50-59 years, 60-69 years, and 70-74 years were 1.7, 3.3, 3.8, and 2.6 years, respectively. CONCLUSIONS: These results suggest that much, although not all, of the smaller effect of screening on mortality in women aged 40-49 years is due to faster progression of a substantial proportion of tumors in this age group and the rapid increase in incidence during this decade of life. It is concluded that the interval between screenings should be shortened to achieve a greater benefit in this age group. It is estimated that a 19% reduction in mortality would result from an annual screening regime.

Adult↗
PubMed1995

Stopping drinking and risk of oesophageal cancer.

OBJECTIVE: To examine the effect of stopping drinking on the risk of oesophageal cancer. DESIGN: Hospital based case-control study. SETTING: Surgical departments of four district general hospitals and general practices in Hong Kong. SUBJECTS: Cases were 400 consecutive admissions of patients with histologically confirmed diagnosis of oesophageal cancer during a 21 month period in 1989-90 (87% response rate). Controls were 1598 patients selected from the same surgical departments as the cases and from the general practices from which the cases were originally referred (95% response rate). MAIN OUTCOME MEASURE: Relative risk of developing oesophageal cancer after stopping drinking (adjusted for age, education, place of birth, smoking, and diet). RESULTS: Current light drinking (< 200g ethanol/week) was not associated with significant increase in risk. Among former drinkers risk fell more quickly in moderate (200-599 g/week) than heavy (> or = 600 g/week) drinkers. Even among heavy drinkers, however, risk had dropped substantially after five to nine years of not drinking. The results suggest that the time taken for risk to return to that in subjects who never drink was 10-14 years for moderate drinkers and 15 years or more, if ever, for heavy drinkers. CONCLUSION: Risk of oesophageal cancer decreases fairly rapidly with time after abstaining from drinking. This new finding could be used in health promotion to encourage behavioural changes, especially in heavy drinkers, who have a very high risk of developing oesophageal cancer. It also suggests that alcoholic beverages have a strong effect on the late stage of carcinogenesis.

Adenocarcinoma↗
PubMed1995

Oesophageal cancer in never-smokers and never-drinkers.

Alcohol, tobacco and diet are the most important determinants of oesophageal cancer. Previous studies which examined smoking in non-drinkers and drinking in non-smokers did not report the main effects of dietary factors or the smoking and drinking effects adjusted for dietary factors. Data from a hospital-based case-control study in Hong Kong Chinese were used to examine the effects of dietary variables as well as tobacco and alcohol in never-drinkers and never-smokers. Among the 400 cases, there were 68 never-smokers and 53 never-drinkers; 540 were never-smokers and 407 were never-drinkers among 1598 controls. In never-smokers, alcohol drinking was strongly associated with risk. Use of green leafy vegetables and citrus fruits was protective. Among never-drinkers, smokers had increased risk, but the protective effect of vegetables and fruits did not reach statistical significance. In never-smokers and in never-drinkers alike, frequent consumption of pickled vegetables and being born in Teochew or Hokkien were associated with increased risks. This study provides further support for the independent effects of alcohol, tobacco and diet in oesophageal cancer.

Aged↗
PubMed1995

Familial risk, abortion and their interactive effect on the risk of breast cancer--a combined analysis of six case-control studies.

In a previous study in France, we reported that the relative risk of breast cancer associated with a family history of breast cancer was higher in those subjects with a history of abortions. The present study was undertaken to check the existence of this interaction in other studies and to investigate whether the interaction is modified by the time at which abortions occur. Data were obtained from six case-control studies in France, Australia and Russia, with information on family history of breast cancer and abortion for 2693 breast cancer cases and 3493 controls. The interaction effect was estimated in each study separately, then combined using a multivariate weighted average. The relative risk conferred by a family history of breast cancer increased with the number of abortions (1.8 for no abortion, 1.9 for one abortion, 2.8 for two or more). There was a significant interaction between total number of abortions and family history (P = 0.04), but this was no longer significant when adjusted for other risk factors. The familial risk was highest for those who had had an abortion before first childbirth (1.9 for abortion after first childbirth, 2.7 for abortion before first childbirth). The adjusted risk associated with family history was significantly higher in those with an abortion before first childbirth (P = 0.04). Our findings suggest a synergism between familial factors and abortion. The interaction was not substantially modified by the type of abortion (spontaneous or induced) but was modified by the time at which it occurred in relation to first childbirth. This suggests an effect of abortion itself rather than predisposition to abortion. Further studies of breast cancer cases, particularly among BRCA1 gene carriers and their families, could improve our understanding of this effect.

Abortion, Induced↗
PubMed1995

Effect of breast cancer screening after age 65.

OBJECTIVE: To assess the effect of mammographic screening for breast cancer in women aged 65 years or over. SETTING: The Swedish two county trial of screening for breast cancer, in which 77,080 women aged 40-74 (21,925 aged 65-74) were randomly allocated to receive regular mammographic screening for breast cancer, and 55,985 women aged 40-74 (15,344 aged 65-74) were allocated to an unscreened control group. METHODS: One group was screened every 33 months on average, except for those aged 40-49 at randomisation who were screened every 24 months. The control group was screened once at the conclusion of the trial. The main statistical analysis was the comparison of cumulative mortality with 13 years of follow up between the screened and control groups, in age groups 50-64 and 65-74, using Poisson regression. This was complemented by subsidiary analyses assessing the lead time, sensitivity, and predicted mortality from the size, node status, and grade of tumours diagnosed in the screened and control groups. RESULTS: In the age group 65-74 at randomisation there was a significant reduction in breast cancer mortality in the screened group, with a relative mortality of 0.68 and 95% confidence interval of 0.51 to 0.89. This was backed up by the results of the analyses of lead time, sensitivity, and tumour characteristics. CONCLUSIONS: Women aged 65 or more who are regularly screened can expect a reduced risk of dying from breast cancer.

Adult↗
PubMed1995

Screening for breast cancer in women aged under 50: mode of detection, incidence, fatality, and histology.

OBJECTIVE: To assess the effect of screening for breast cancer in women aged 40-49 in the Swedish two county trial, in terms of mortality reduction, advanced cancer reduction, mode of detection, and the histology of tumours detected. SETTING: The Swedish two county trial of screening for breast cancer, in which 77,080 women aged 40-74 (19,844 aged 40-49) were randomly allocated to receive regular invitation to mammographic screening for breast cancer, and 55,985 women aged 40-74 (15,604 aged 40-49) were allocated to an unscreened control group. METHODS: The screening interval in the younger age group was two years and in the older age group about three years. Statistical analysis of mortality and incidence rates was performed by Poisson regression. Relative survival was estimated using proportional hazards regression. RESULTS: The relative mortality for the group invited to screening compared with the control group was 0.87 (95% confidence interval 0.54 to 1.41) in the 40-49 age group, in close agreement with the relative incidence of advanced cancers. For Kopparberg county the relative mortality was 0.73 (95% CI 0.37 to 1.41) and for Ostergotland 1.02 (95% CI 0.52 to 1.99). The lesser effect in the 40-49 group as a whole was largely due to a higher rate of interval cancers in this age group, and the occurrence in Ostergotland of a higher number of cancers after randomisation, but before screening started, and in women who refused screening. The higher interval cancer rate was consistent with the higher proportion of ductal grade 3 and medullary cancers in women aged 40-49 at diagnosis. CONCLUSIONS: A major difficulty in screening women aged 40-49 is the rapid progression of a subset of tumours arising in this age group. Shortening the screening interval from two years would be necessary to achieve a higher mortality reduction.

Adult↗