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Feasibility of screening for breast cancer
Abstract
The feasibility of screening for breast cancer by clinical examination and X-ray mammography has been studied. The results suggest that a breast screening programme is safe from dangers of irradiation and can be conducted by non-medical staff. The response of women at risk suggests that the service is acceptable to the general public. The hospital service could deal with the additional surgical work.
In 1986, a project began to assess the feasibility of mobile breast screening, using oblique view mammography, in rural areas near Edinburgh. One of the aims of the project was to determine the feasibility, in terms of accuracy and cost, of non‐radiologist prescreeners. The sensitivity and specificity of each reader was calculated (using 12‐month interval cancer rates). Sensitivities of 80%, 80% and 83% were found for a radiographer, a non‐radiologist doctor and a radiologist respectively, with corresponding specificities of 78%, 84% and 86%.
When each reader was costed, prescreening was no cheaper than the radiologist reading all the films himself (£79.10 for the radiologist reading 1,000 pairs of films alone, against £84.97 with the radiographer prescreening and £163.93 with the non‐radiologist doctor prescreening). We were unable to demonstrate any advantages of prescreening, but found that double reading of the films, though costly, would have increased the sensitivity of the programme.
In a feasibility study of mass population screening for breast cancer by clinical examination and mammography the ability of non-medical staff (nurses and radiographers) to act as primary screeners was compared with that of medical staff (surgeons and radiologists). In 240 women with cancer the rate of detection of the disease by the non-medical staff was comparable to that of the medical staff, although the non-medical staff detected more cancers by mammography alone than did the medical staff. The rate of detection by surgeons and particularly nurses was lower in women without symptoms than in those with symptoms, whereas the incidence of detection by radiologists and radiographers was lower in women aged under 50 than in those over 50. The rate of detection by all groups of staff significantly increased with increases in tumour size. The results suggest that non-medical staff can act effectively as primary screeners, but that for the detection of cancer in asymptomatic women, particularly those over 50, mammography is probably more effective than clinical examination.
In a feasibility study of mass population screening for breast cancer by annual clinical examination and mammography the findings of non-medical staff (nurses and radiographers) were used to estimate the hospital work load generated by such a programme. Among 2490 women who attended for the first time by invitation the rate of referral for a surgical opinion based on the findings of the non-medical staff was 7.9% and the biopsy rate 2.5%. In the second and third years referral rates fell to 4.3% and 2.7% respectively and the biopsy rates to 1.1% and 1.4%. The rates of referral and biopsy among 1203 women who referred themselves for screening were higher, but many self-referred women were symptomatic; those without symptoms had rates of referral and biopsy similar to those of the invited women. Extrapolation of these findings to a population of 200,000 in a typical health district showed that the hospital work load would be high in the first year of screening with 44 outpatient referrals per week and 14 biopsies. By the third year, however, only seven referrals and four biopsies a week could be expected. The work load would be reduced by a third if screening were confined to women over the age of 50.
Data from a telephone survey of women participating in a federally funded screening program were used to demonstrate the sensitivity of mammography compliance estimates to varying definitions of the time interval within which women are considered compliant with screening guidelines and what constitutes a true screening (as opposed to diagnostic) mammogram. The survival analysis approach used reveals patterns concealed by other approaches to measuring mammography behavior and provides a means for quantifying the impact of various definitional choices on compliance estimates. The results suggest that, although variations in defining and excluding potential diagnostic mammograms lead to differences in compliance measures no greater than 6%, differences as small as 1 month in the screening interval definition used can produce differences in compliance estimates as large as 27%. These results call into question the comparability of estimates across studies and suggest that standard measures would greatly facilitate future efforts in understanding how to promote compliance with mammography screening guidelines.