Mammography Screening - Health - Lecture Slides, Slides of Public Health

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Overdiagnosis in mammography screening for breast cancer in Sweden and Norway docsity.com The aim of mammography screening is to diagnose the tumour when it is small and before tumour spread occurs since such small stage I tumours have favourable prognosis. docsity.com Ductal breast carcinoma Lobular breast carcinoma docsity.com Overdiagnosis is the diagnosis of disease that (without screening) would not have given symptoms during the lifetime of the patient Definition: docsity.com May these three factors explain the incidence increase? • There was an underlying increase in breast cancer incidence rates in the periods before the screening programmes started. • In the first screening round a large number of slow-growing tumours that would have occurred in the future are diagnosed earlier. • In the following screening rounds some excess of breast cancer will persist due to a combined effect of lead-time and incidence increase with age. docsity.com During the introduction of mammography screening in Sweden the breast cancer incidence increased by nearly 50% in the screened age group. No similar fall in breast cancer incidence in women above age 70 years has emerged. 0 50 100 150 200 250 300 350 400 19 71 19 73 19 75 19 77 19 79 19 81 19 83 19 85 19 87 19 89 19 91 19 93 19 95 19 97 19 99 20 01 Incidence per 100 000 women Sweden 70+ Sweden 50-69 Sweden 30-49 docsity.com Overdiagnosis in the Swedish screening programme • The incidence increase is 50% in the age group 50-69 years. • The incidence decline is 0% in the age group 70-74 years and 12% in the age group 75-79 years. This decrease compensates less than 3% of the incidence increase in the screened age group. No incidence decline is expected among women above age 79 years. • We conclude that nearly all of the incidence increase in Sweden are caused by cancers that would not have been diagnosed in the absence of screening. docsity.com During the introduction of mammography screening in Norway the breast cancer incidence increased >50% in the screened age groups. Only an 11 % reduction in breast cancer incidence occurred in previously screened women aged 70-74 yrs in 2000-1. 0 50 100 150 200 250 300 350 400 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 Incidence per 100 000 women Norway 70+ Norway 50-69 AORH-counties Non-AORH-counties Norway 30-49 docsity.com Incidence rates among those attending and those not attending screening in the age group 50-69 years in four Norwegian counties 0 50 100 150 200 250 300 350 400 Before screening (1991-95) Not attending screening (1996- 2001) Second screening round (1998-99 ) Third screening round (2000-1) Incidence per 100 000 women docsity.com • Interval cancer is breast cancer detected clinically in the time interval between two mammography screenings. • The incidence rate of interval cancer in the Norwegian screening programme has been 190 cases per 100 000 per 2 year (i.e. close to 50% of the predicted rate in the absence of screening). • Compared to the incidence rate of cancer in the absence of screening, the rate of interval cancer is 30% in the first year and 70% in the second year after screening. Definition of interval cancer docsity.com Cancer incidence in those leaving the screening program at age 69 years reflects the interval cancer incidence If the incidence reduction is 70% in the first year, 30% in the second year, 15 % in the third year, 5% in the fourth year and return to the background in the fifth year, the overall reduction in age group 70-74 year is 13% (assuming 75% attendance rate at the last screening at age 68-69 years). docsity.com In the randomized screening trials the mortality decline was observed after four years. Since Sweden started mammography screening more than ten years before Norway one would expect: 1. In the 1990s the decline in the Swedish breast cancer mortality rates should be substantially larger than the decline in the Norwegian rates. 2. In Sweden the breast cancer mortality rates should decline substantially more in the age group 55-74 years than in the other age groups. As shown in the next slide none of these phenomena have been observed. docsity.com Age-adjusted breast cancer mortality rates in Norway and Sweden in 1978-2001 for the age groups 45-54, 55-74 and 75-84 years 0 40 80 120 160 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 Deaths per 100 000 Age 75-84 Age 55-74 Age 45-54 years docsity.com What is known about overdiagnosed cancers in other locations? • Screening for prostate cancer leads to 30% overdiagnosis (Etzioni et al, JNCI 2002). In this organ sub-clinical cancer is very frequent at autopsy (prevalence 50% after age 80 years, Liavag I, Harbitz TB, Haugen OA. Latent carcinoma of the prostate. Recent Results Cancer Res. 1972;39:131-7). • Screening of children for neuroblastoma leads to substantial overdiagnosis. For such tumours spontaneous regression without treatment is the most likely outcome, therefore these patients do not benefit from earlier diagnosis (Schilling et al, N Eng J Med 2002). docsity.com