244
other professional staff throughout the NHS, health economists, the Medical Research Council, and charities. It should be possible to develop protocols that will demonstrate the cost effectiveness of these research initiatives, and this ought to help immensely in the competition for research funds. The whole clinical community should work together to provide the evidence needed to sustain the argument that more money spent on clinical research will be beneficial in improving the cost effectiveness and clinical efficacy of the NHS. United Medical and Dental Schools of Guy’s and St Thomas’s Hospitals, London SE1 9RT, UK
fatality rate); finally almost 25% of controls had mammograms outside the screening programme, most of these women having symptoms. In discussions that followed publication of our trial results from case-control studies were used to support the view that mammographic screening reduces breast cancer mortality. Methodologically, the controlled trial and the case-control study are not comparable: the trial assesses the effect of an invitation to screening whereas the case-control method looks at the benefit for those who do attend. The two approaches yield different outcomesa:
C. CHANTLER,
Malmo study, assessed as clinical trial Invited Controls
Member, NHS Policy Board
(n=21 088)
can Americans learn from Europeans. In: Health care systems in transition. Paris: Office of Economic Cooperation and Development, 1990 87-101.
1. Jonsson P. What
Transcendental
Breast
explanations and near-death experience
Malmo
interpretations. Oxford University Clinical Pharmacology Department, Radcliffe Infirmary, Oxford OX2 6HE, UK 1. 2.
3
KARL L.
R. JANSEN
Siegel RK. The psychology of life after death Am Psychol 1980; 35: 911-30. Siegel RK. Phencyclidine and ketamine intoxication: a study of recreational users. In. Peterson RC, Stillman RC, eds. Phencyclidine abuse. an appraisal Maryland National Institute of Drug Abuse, 1978: 119-50 Grinspoon L, Bakalar SB. Psychedelic drugs reconsidered. New York Basic Books, 1981.
4. Jansen K Near death experience and the NMDA receptor Br Med J 1989, 298: 1708.
Screening mammography SIR,—The effect of mammographic screening on breast cancer mortality has been assessed in three clinical trials and three case-control studies.l-6 The odds ratio, calculated from case-control studies, of the proportions of ever screened/never screened among women dying from breast cancer and among age-matched living controls has been used as a measure of the risk reduction that might be achieved in controlled trials. The Malmö trial3 showed, unlike the two-countries study from Sweden2 and the HIP study from New York,’ no clear-cut reduction in mortality from breast cancer in the invited group. The trend in women above 55 years of age at invitation was in line with findings in the two-countries and HIP studies, and it was concluded that mammographic screening, at least in women over 55, might lead to reduced breast cancer
mortality. Our explanation for the lack of a signficant reduction in overall breast cancer mortality was the high prevalence of advanced breast cancer among women not attending screening. Furthermore 100 of the 588 cancers in the invited group were detected in intervals between screenings (these cases had a higher than average case
deaths
(n=21195)
63 (0 0 299%) 66 (0.311 %l Relative risk = 0-96 (0 68-1-35)
study, handled as Took part
case- control approach’ Dead from Living
controls breast cancer screening (n 300) (n = 60) programme 229 36 Yes 71 24 No Crude odds ratio 0 46; adjusted (matching for age) for = 0-42 (95% CI 0 22-0 78)
SIR,-Dr Owens (Nov 10, p 1175) and your subsequent correspondents (Jan 12, p 116) describe data that are claimed to support psychological, physiological, and transcendental interpretations of the near-death experience. However, although the evidence clearly supports the first two interpretations, the highly controversial transcendental interpretation, which contradicts the widely held basic paradigms of physical science, is based solely on the perception of dying persons that their cognitive functioning is improved. Owens claims that this supports a transcendental explanation because individuals near death tend to have impaired cognitive functioning due to cerebral disturbances. However, this claim is completely unwarranted without objective testing of cognitive functioning in these patients. People who have taken powerful hallucinogenic drugs such as lysergide and ketamine, which are known to cause considerable cerebral disturbance, may claim great insights and much improved cerebral functioning.!-A Objective testing, however, does not support their selfperception-nor would it seem likely to do so in dying patients. Until objective testing of the cognitive function in dying persons claiming improved function is done the well established paradigms of physical science stand firm against transcendental
cancer
=
signficant risk reduction in mammographic screening trial, the odds ratio being seen in other published studies. There
seems to
be
a
the Malino in the range
This risk reduction was a clear contrast to the result from the clinical trial. 31 of the 63 women who died from breast cancer in the invited group were non-participants in the clinical trial. By the end of December, 1986, 29% of breast cancer cases among nonattenders and 20% of the cases with interval carcinoma had died. This is in striking contrast to the 3% among women with cancer detected at screening. The higher mortality among non-attenders is explained by the higher proportion of advanced cases. The breast cancer incidence among non-attenders did not differ from that among the controls. A comparison of the breast cancer incidence in these two groups would therefore give no valid estimate of the selection bias caused by non-attenders. If the case-control method is to be used to assess the public health effect of mammographic screening, selection bias caused by non-response must be allowed for. Departments of Community Health Sciences and Diagnostic Radiology, Lund University, Malmo General Hospital, S-214 01 Malmo, Sweden
BO GULLBERG INGVAR ANDERSSON LARS JANZON JONAS RANSTAM
Strax P, Venet L Periodic breast cancer screening in reducing mortality from breast cancer. JAMA 1971, 215: 1777-85. 2 Tabár L, Gad A, Holmberg LH, et al Reduction m mortality from breast cancer after mass screening with mammography Lancet 1985, 829-52 3. Andersson I, Aspegren K, Janzon L, et al. Mammographic screening and mortality from breast cancer the Malmo mammographic screening trial Br Med J1988; 297: 943-48 4. Palli D, Rosselli Del Torco M, Buiatti E, et al A case-control study of the effecacy of a non-randomized breast cancer screening program in Florence (Italy) Int J Cancer 1
Shapiro S,
1986; 38: 501-04. ALM, Holland R, Sturmans F, et al Reduction of breast cancer mortality through mass screening with modem mammography Lancet 1984, i :1222-24 6. Collette HJA, Rombach JJ, Day NE, et al Evaluation of screening for breast cancer in a non-randomised study (the DOM project) by means of a case-control study 5. Verbeek
Lancet 1984; i:224-26.
Proton
magnetic resonance spectroscopy in chronic renal failure
SIR,—Patients with chronic renal failure experience cognitive computerised axial tomography may demonstrate cerebral atrophy.2 However, no clear relation has been shown between the degree of cognitive deficit and the imaging abnormality.2 Proton magnetic resonance spectroscopy (’H-MRS) of the brain shows prominent resonances from N-acetyl aspartate (NAA), choline-containing compounds (Cho), and creatine and phosphocreatine (Cr).3 NAA is thought to be located primarily in deficits!,2 and
other professional staff throughout the NHS, health economists, the Medical Research Council, and charities. It should be possible to develop protocols that will demonstrate the cost effectiveness of these research initiatives, and this ought to help immensely in the competition for research funds. The whole clinical community should work together to provide the evidence needed to sustain the argument that more money spent on clinical research will be beneficial in improving the cost effectiveness and clinical efficacy of the NHS. United Medical and Dental Schools of Guy’s and St Thomas’s Hospitals, London SE1 9RT, UK
fatality rate); finally almost 25% of controls had mammograms outside the screening programme, most of these women having symptoms. In discussions that followed publication of our trial results from case-control studies were used to support the view that mammographic screening reduces breast cancer mortality. Methodologically, the controlled trial and the case-control study are not comparable: the trial assesses the effect of an invitation to screening whereas the case-control method looks at the benefit for those who do attend. The two approaches yield different outcomesa:
C. CHANTLER,
Malmo study, assessed as clinical trial Invited Controls
Member, NHS Policy Board
(n=21 088)
can Americans learn from Europeans. In: Health care systems in transition. Paris: Office of Economic Cooperation and Development, 1990 87-101.
1. Jonsson P. What
Transcendental
Breast
explanations and near-death experience
Malmo
interpretations. Oxford University Clinical Pharmacology Department, Radcliffe Infirmary, Oxford OX2 6HE, UK 1. 2.
3
KARL L.
R. JANSEN
Siegel RK. The psychology of life after death Am Psychol 1980; 35: 911-30. Siegel RK. Phencyclidine and ketamine intoxication: a study of recreational users. In. Peterson RC, Stillman RC, eds. Phencyclidine abuse. an appraisal Maryland National Institute of Drug Abuse, 1978: 119-50 Grinspoon L, Bakalar SB. Psychedelic drugs reconsidered. New York Basic Books, 1981.
4. Jansen K Near death experience and the NMDA receptor Br Med J 1989, 298: 1708.
Screening mammography SIR,—The effect of mammographic screening on breast cancer mortality has been assessed in three clinical trials and three case-control studies.l-6 The odds ratio, calculated from case-control studies, of the proportions of ever screened/never screened among women dying from breast cancer and among age-matched living controls has been used as a measure of the risk reduction that might be achieved in controlled trials. The Malmö trial3 showed, unlike the two-countries study from Sweden2 and the HIP study from New York,’ no clear-cut reduction in mortality from breast cancer in the invited group. The trend in women above 55 years of age at invitation was in line with findings in the two-countries and HIP studies, and it was concluded that mammographic screening, at least in women over 55, might lead to reduced breast cancer
mortality. Our explanation for the lack of a signficant reduction in overall breast cancer mortality was the high prevalence of advanced breast cancer among women not attending screening. Furthermore 100 of the 588 cancers in the invited group were detected in intervals between screenings (these cases had a higher than average case
deaths
(n=21195)
63 (0 0 299%) 66 (0.311 %l Relative risk = 0-96 (0 68-1-35)
study, handled as Took part
case- control approach’ Dead from Living
controls breast cancer screening (n 300) (n = 60) programme 229 36 Yes 71 24 No Crude odds ratio 0 46; adjusted (matching for age) for = 0-42 (95% CI 0 22-0 78)
SIR,-Dr Owens (Nov 10, p 1175) and your subsequent correspondents (Jan 12, p 116) describe data that are claimed to support psychological, physiological, and transcendental interpretations of the near-death experience. However, although the evidence clearly supports the first two interpretations, the highly controversial transcendental interpretation, which contradicts the widely held basic paradigms of physical science, is based solely on the perception of dying persons that their cognitive functioning is improved. Owens claims that this supports a transcendental explanation because individuals near death tend to have impaired cognitive functioning due to cerebral disturbances. However, this claim is completely unwarranted without objective testing of cognitive functioning in these patients. People who have taken powerful hallucinogenic drugs such as lysergide and ketamine, which are known to cause considerable cerebral disturbance, may claim great insights and much improved cerebral functioning.!-A Objective testing, however, does not support their selfperception-nor would it seem likely to do so in dying patients. Until objective testing of the cognitive function in dying persons claiming improved function is done the well established paradigms of physical science stand firm against transcendental
cancer
=
signficant risk reduction in mammographic screening trial, the odds ratio being seen in other published studies. There
seems to
be
a
the Malino in the range
This risk reduction was a clear contrast to the result from the clinical trial. 31 of the 63 women who died from breast cancer in the invited group were non-participants in the clinical trial. By the end of December, 1986, 29% of breast cancer cases among nonattenders and 20% of the cases with interval carcinoma had died. This is in striking contrast to the 3% among women with cancer detected at screening. The higher mortality among non-attenders is explained by the higher proportion of advanced cases. The breast cancer incidence among non-attenders did not differ from that among the controls. A comparison of the breast cancer incidence in these two groups would therefore give no valid estimate of the selection bias caused by non-attenders. If the case-control method is to be used to assess the public health effect of mammographic screening, selection bias caused by non-response must be allowed for. Departments of Community Health Sciences and Diagnostic Radiology, Lund University, Malmo General Hospital, S-214 01 Malmo, Sweden
BO GULLBERG INGVAR ANDERSSON LARS JANZON JONAS RANSTAM
Strax P, Venet L Periodic breast cancer screening in reducing mortality from breast cancer. JAMA 1971, 215: 1777-85. 2 Tabár L, Gad A, Holmberg LH, et al Reduction m mortality from breast cancer after mass screening with mammography Lancet 1985, 829-52 3. Andersson I, Aspegren K, Janzon L, et al. Mammographic screening and mortality from breast cancer the Malmo mammographic screening trial Br Med J1988; 297: 943-48 4. Palli D, Rosselli Del Torco M, Buiatti E, et al A case-control study of the effecacy of a non-randomized breast cancer screening program in Florence (Italy) Int J Cancer 1
Shapiro S,
1986; 38: 501-04. ALM, Holland R, Sturmans F, et al Reduction of breast cancer mortality through mass screening with modem mammography Lancet 1984, i :1222-24 6. Collette HJA, Rombach JJ, Day NE, et al Evaluation of screening for breast cancer in a non-randomised study (the DOM project) by means of a case-control study 5. Verbeek
Lancet 1984; i:224-26.
Proton
magnetic resonance spectroscopy in chronic renal failure
SIR,—Patients with chronic renal failure experience cognitive computerised axial tomography may demonstrate cerebral atrophy.2 However, no clear relation has been shown between the degree of cognitive deficit and the imaging abnormality.2 Proton magnetic resonance spectroscopy (’H-MRS) of the brain shows prominent resonances from N-acetyl aspartate (NAA), choline-containing compounds (Cho), and creatine and phosphocreatine (Cr).3 NAA is thought to be located primarily in deficits!,2 and
