1143
suspicious abnormality if she has breast cancer whereas this is virtually impossible if she has cervical carcinoma-in-situ. a
University Department of Community Medicine, Stopford Building, Oxford Road,
ALWYN SMITH IAN LECK
Manchester M13 9PT.
SCREENING FOR BREAST CANCER
SIR,-Dr Thomas (Nov. 8, p. 914) indicates that the aim of is to examine the feasibility of screening high-risk for breast cancer; she describes the methods used and some preliminary findings. This is very useful when contemplating screening for breast cancer, but such descriptive data cannot be used to define policy in this field. The chief question is not whether screening can be donebut does it work? This is, of course, an extremely complex issue, as has been indicated’ in your series of articles on screening. If it is shown that survival can be improved in those who are screened, the next question is whether the N.H.S. should introduce screening: this depends on the relative benefits and disadvantages of screening and the investment of effort in screening. This is the main strategic problem; but there are important subsidiary issues. Once a woman has presented to a diagnostic service, what is the optimum tactic for reaching a definitive diagnosis? With breast cancer, this requires consideration of the value of history, clinical examination, and a range of investigations. Mammography, xerography, or thermography have been indicated as a first level of investigation. Other investigations include bone-scan, biochemical tests for dissemination of disease, and the use of aspiration or open biopsy. Further information is needed on the relative weight to be placed on the different items and the appropriate combination of steps in the diagnostic process. Once a woman has been shown not to have breast cancer, arrangements should be made for follow-up. Again there is need for clear guidance as to whether no further care, self-palpation, reattendance with symptoms, or reattendance for regular check-up are required; for those called up at regular intervals, what is the optimum interval and what information should be collected when they return? It is not clear from Dr Thomas’s article whether future activities at Guildford will be so adjusted that they provide answers to these questions. Even if the strategic question on the effectiveness and efficiency of breast-cancer screening cannot be answered, there are a number of important and unresolved issues at the tactical level. Respondents should follow different planned pathways through the maze of initial screen, detailed investigation for definitive diagnosis, or follow-up. Only when examinees have been subjected to such planned study will it be possible to identify the best approach to diagnosis and follow-up. her
study
women
Institute of Cancer Research, Block E, Clifton Avenue, Sutton, Surrey SM2 5PX.
MICHAEL ALDERSON
FLUOROCARBONS AND THE OZONE SHIELD
SIR,-Your editorial (Oct. 4, p. 647) omitted much information that would be useful to your readers in making a judgment on the fluorocarbon/ozone issue. First, there is a consensus in the scientific community that the work of Molina and Rowland2 still has the status of hypothesis and that much scientific work is necessary to determine its validity. This work is now going forward with support from government and industry, and enough information should be in hand by 1978 to allow a reasonable scientific de1. Holland, W. W. Lancet, 1974, ii, 1494. 2 Molina, M. J., Rowland, F. S. Nature, 1974,
whether fluorocarbons are the cause of any signifidepletion. Research completed so far has led to several adjustments in elements of the theory that have resulted in a large reduction in the predicted impact-if, indeed, the theory proves to be correct. Work by Dr Paul J. Crutzen, of the National Center for Atmospheric Research, now shows that if predictions of the fluorocarbon/ozone-depletion theory are fully correct and fluorocarbon production were stopped immediately, the ozone depletion from all fluorocarbons produced worldwide to date would be about 1.2% in 1985, with a gradual return to normal thereafter-not the 7-18% depletion you report. By continuing worldwide production of fluorocarbons for 3 more years, the added depletion of the ozone-if the theory is valid-would be an additional 0.5% by 1990, with a rise to normal levels after that. cision
on
cant ozone
The significance of an added 0-5% ozone depletion is readily understood by relating it to the natural thinning of the ozone from the poles to the equator. This natural thinning results in there being about 1% less ozone over one’s head for each degree of latitude (70 miles) one moves towards the equator. Thus 0.5% ozone depletion poses about the same risk to increased ultraviolet exposure as moving 35 miles away from the pole. With a risk factor so small as to be unmeasurable, given the natural fluctuations of the ozone layer, there certainly is time to complete the scientific programme before deciding whether any regulation of fluorocarbon use is necessary. Far from being "unimpressed" by the fluorocarbon/ozone theory, as The Lancet reports, industry has been very much impressed by the good theoretical science this theory represents-so much so, in fact, that it is sponsoring research at nearly 20 universities and independent laboratories in the U.S. and abroad to test critical elements of the theory. This industry-sponsored research is expected to cost more than$5 million over a 3-year period. The most critical elements of the research
of the chlorine-oxide radical in the of tropospheric and stratospheric and into alternative destructive mechchlorine, anisms for fluorocarbons. The chlorine inventories are crucial. They will permit scientific interpretation of chlorine-oxide radical measurements and calculation of the extent of the repeating action between chlorine and ozone. The fact that an ozone/chlorine catalytic chain reaction occurs in the laboratory is generally acknowledged. There is serious and quite legitimate question, however, as to the extent to which this same reaction occurs in the stratosphere, where competing reactions not present under laboratory conditions may well exist. If this catalytic chain reaction does not occur the many thousands of times postulated by the fluorocarbon/ozone theory, there may well be no fluorocarbon/ozone problem.
include
measurement
stratosphere,
inventory investigation
an
Another minor error in your article is the identification of the Consumer Product Safety Commission as "an independent pressure group". The Commission is a fully fledged U.S. Government agency with power to restrict the use of consumer goods. You failed also to note that both this Commission and the U.S. Food and Drug Administration have rejected petitions to ban the use of fluorocarbon propellants. Both agencies have stated that there is no scientific justification for a ban. In addition, Dr H. Guyford Stever, Director of the National Science Foundation, and Dr James Fletcher, Director of the National Aeronautics and Space Administration, have commented in Congressional hearings that much scientific work on the issue needs to be done and that there is no significant risk in taking the time to do this research. The
ozone-depletion theory has raised some serious quesmost certainly indicates a need for further study. more information becomes available, it is increasingly
tions, and it
But as apparent that a call for control at this time is premature and cannot be justified on scientific grounds. E. I. du Pont de Nemours & Company, Wilmington, Delaware 19898,
249, 810.
U.S.A.
T. L. CAIRNS
suspicious abnormality if she has breast cancer whereas this is virtually impossible if she has cervical carcinoma-in-situ. a
University Department of Community Medicine, Stopford Building, Oxford Road,
ALWYN SMITH IAN LECK
Manchester M13 9PT.
SCREENING FOR BREAST CANCER
SIR,-Dr Thomas (Nov. 8, p. 914) indicates that the aim of is to examine the feasibility of screening high-risk for breast cancer; she describes the methods used and some preliminary findings. This is very useful when contemplating screening for breast cancer, but such descriptive data cannot be used to define policy in this field. The chief question is not whether screening can be donebut does it work? This is, of course, an extremely complex issue, as has been indicated’ in your series of articles on screening. If it is shown that survival can be improved in those who are screened, the next question is whether the N.H.S. should introduce screening: this depends on the relative benefits and disadvantages of screening and the investment of effort in screening. This is the main strategic problem; but there are important subsidiary issues. Once a woman has presented to a diagnostic service, what is the optimum tactic for reaching a definitive diagnosis? With breast cancer, this requires consideration of the value of history, clinical examination, and a range of investigations. Mammography, xerography, or thermography have been indicated as a first level of investigation. Other investigations include bone-scan, biochemical tests for dissemination of disease, and the use of aspiration or open biopsy. Further information is needed on the relative weight to be placed on the different items and the appropriate combination of steps in the diagnostic process. Once a woman has been shown not to have breast cancer, arrangements should be made for follow-up. Again there is need for clear guidance as to whether no further care, self-palpation, reattendance with symptoms, or reattendance for regular check-up are required; for those called up at regular intervals, what is the optimum interval and what information should be collected when they return? It is not clear from Dr Thomas’s article whether future activities at Guildford will be so adjusted that they provide answers to these questions. Even if the strategic question on the effectiveness and efficiency of breast-cancer screening cannot be answered, there are a number of important and unresolved issues at the tactical level. Respondents should follow different planned pathways through the maze of initial screen, detailed investigation for definitive diagnosis, or follow-up. Only when examinees have been subjected to such planned study will it be possible to identify the best approach to diagnosis and follow-up. her
study
women
Institute of Cancer Research, Block E, Clifton Avenue, Sutton, Surrey SM2 5PX.
MICHAEL ALDERSON
FLUOROCARBONS AND THE OZONE SHIELD
SIR,-Your editorial (Oct. 4, p. 647) omitted much information that would be useful to your readers in making a judgment on the fluorocarbon/ozone issue. First, there is a consensus in the scientific community that the work of Molina and Rowland2 still has the status of hypothesis and that much scientific work is necessary to determine its validity. This work is now going forward with support from government and industry, and enough information should be in hand by 1978 to allow a reasonable scientific de1. Holland, W. W. Lancet, 1974, ii, 1494. 2 Molina, M. J., Rowland, F. S. Nature, 1974,
whether fluorocarbons are the cause of any signifidepletion. Research completed so far has led to several adjustments in elements of the theory that have resulted in a large reduction in the predicted impact-if, indeed, the theory proves to be correct. Work by Dr Paul J. Crutzen, of the National Center for Atmospheric Research, now shows that if predictions of the fluorocarbon/ozone-depletion theory are fully correct and fluorocarbon production were stopped immediately, the ozone depletion from all fluorocarbons produced worldwide to date would be about 1.2% in 1985, with a gradual return to normal thereafter-not the 7-18% depletion you report. By continuing worldwide production of fluorocarbons for 3 more years, the added depletion of the ozone-if the theory is valid-would be an additional 0.5% by 1990, with a rise to normal levels after that. cision
on
cant ozone
The significance of an added 0-5% ozone depletion is readily understood by relating it to the natural thinning of the ozone from the poles to the equator. This natural thinning results in there being about 1% less ozone over one’s head for each degree of latitude (70 miles) one moves towards the equator. Thus 0.5% ozone depletion poses about the same risk to increased ultraviolet exposure as moving 35 miles away from the pole. With a risk factor so small as to be unmeasurable, given the natural fluctuations of the ozone layer, there certainly is time to complete the scientific programme before deciding whether any regulation of fluorocarbon use is necessary. Far from being "unimpressed" by the fluorocarbon/ozone theory, as The Lancet reports, industry has been very much impressed by the good theoretical science this theory represents-so much so, in fact, that it is sponsoring research at nearly 20 universities and independent laboratories in the U.S. and abroad to test critical elements of the theory. This industry-sponsored research is expected to cost more than$5 million over a 3-year period. The most critical elements of the research
of the chlorine-oxide radical in the of tropospheric and stratospheric and into alternative destructive mechchlorine, anisms for fluorocarbons. The chlorine inventories are crucial. They will permit scientific interpretation of chlorine-oxide radical measurements and calculation of the extent of the repeating action between chlorine and ozone. The fact that an ozone/chlorine catalytic chain reaction occurs in the laboratory is generally acknowledged. There is serious and quite legitimate question, however, as to the extent to which this same reaction occurs in the stratosphere, where competing reactions not present under laboratory conditions may well exist. If this catalytic chain reaction does not occur the many thousands of times postulated by the fluorocarbon/ozone theory, there may well be no fluorocarbon/ozone problem.
include
measurement
stratosphere,
inventory investigation
an
Another minor error in your article is the identification of the Consumer Product Safety Commission as "an independent pressure group". The Commission is a fully fledged U.S. Government agency with power to restrict the use of consumer goods. You failed also to note that both this Commission and the U.S. Food and Drug Administration have rejected petitions to ban the use of fluorocarbon propellants. Both agencies have stated that there is no scientific justification for a ban. In addition, Dr H. Guyford Stever, Director of the National Science Foundation, and Dr James Fletcher, Director of the National Aeronautics and Space Administration, have commented in Congressional hearings that much scientific work on the issue needs to be done and that there is no significant risk in taking the time to do this research. The
ozone-depletion theory has raised some serious quesmost certainly indicates a need for further study. more information becomes available, it is increasingly
tions, and it
But as apparent that a call for control at this time is premature and cannot be justified on scientific grounds. E. I. du Pont de Nemours & Company, Wilmington, Delaware 19898,
249, 810.
U.S.A.
T. L. CAIRNS
