The Canadian National Breast Screening Study-1: breast cancer mortality after 11 to 16 years of follow-up. A randomized screening trial of mammography in women age 40 to 49 years.
BACKGROUND
The efficacy of breast cancer screening in women age 40 to 49 years remains controversial.


OBJECTIVE
To compare breast cancer mortality in 40- to 49-year-old women who received either 1) screening with annual mammography, breast physical examination, and instruction on breast self-examination on 4 or 5 occasions or 2) community care after a single breast physical examination and instruction on breast self-examination.


METHODS
Individually randomized, controlled trial.


METHODS
15 Canadian centers.


METHODS
50 430 volunteers age 40 to 49 years, recruited from January 1980 to March 1985, who were not pregnant, had no previous breast cancer diagnosis, and had not had mammography in the preceding 12 months.


METHODS
Breast physical examination and instruction on breast self-examination preceded random assignment of 25 214 women to receive mammography and annual mammography, breast physical examination, and breast self-examination and 25 216 women to receive usual community care with annual follow-up.


METHODS
Verified breast cancer incidence and cohort mortality through 31 December 1993 and deaths from breast cancer through 30 June 1996.


RESULTS
The 105 breast cancer deaths in the mammography group and 108 breast cancer deaths in the usual care group yielded a cumulative rate ratio, adjusted for mammography done outside the study, of 1.06 (95% CI, 0.80 to 1.40). A total of 592 cases of invasive breast cancer and 71 cases of in situ breast cancer were diagnosed by 31 December 1993 in the mammography group compared with 552 and 29 cases, respectively, in the usual care group. The expected proportions of nonpalpable and small invasive tumors were detected on mammography.


CONCLUSIONS
After 11 to 16 years of follow-up, four or five annual screenings with mammography, breast physical examination, and breast self-examination had not reduced breast cancer mortality compared with usual community care after a single breast physical examination and instruction on breast self-examination. The study data show that true effects of 20% or greater are unlikely.
University of Toronto, Toronto, Canada. a.miller@dkfz-heidelberg.de
Anthony B
AB
Miller
Teresa
T
To
Cornelia J
CJ
Baines
Claus
C
Wall
D000328:Adult; D001943:Breast Neoplasms / Q000175:diagnosis / Q000401:mortality* / Q000517:prevention & control; D016504:Breast Self-Examination / Q000592:standards*; D002170:Canada / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008327:Mammography / Q000592:standards*; D008403:Mass Screening / Q000379:methods / Q000592:standards*; D008875:Middle Aged; D010808:Physical Examination / Q000592:standards*; D011314:Preventive Health Services / Q000592:standards