Background: We previously showed that women with abnormal cytology in breast fluid obtained by nipple aspiration had an increased relative risk (RR) of breast cancer compared with women from whom fluid was not obtained and with women whose fluid had normal cytology. This study extends the follow-up in the original study group (n = 4046) and presents the first follow-up for a second group of women (n = 3627).
Methods: We collected nipple aspirate fluid from women in the San Francisco Bay Area during the period from 1972 through 1991, classified the women according to the most severe epithelial cytology observed in fluid specimens, and determined breast cancer incidence through March 1999. We estimated RRs for breast cancer using Cox regressions, adjusting for age and year of study entry. All statistical tests were two-sided.
Results: For women in the first and second study groups, the median years of follow-up were 21 years and 9 years, respectively, and breast cancer incidences were 7.8% (285 cases in the 3633 women for whom breast cancer status could be determined) and 3.5% (115 of 3271), respectively. Compared with women from whom no fluid was obtained, whose incidences of breast cancer were 4.7% (39 of 825) and 3.3% (65 of 1950) for those in group 1 and group 2, respectively, incidences and adjusted RRs were 8.1% (34 of 422), with RR = 1.4 (95% confidence interval [CI] = 0.9 to 2.3), and 0% (0 of 31), respectively, for those with unsatisfactory aspirate specimens and 8.2% (148 of 1816), with RR = 1.6 (95% CI = 1.1 to 2.3), and 3.1% (25 of 811), with RR = 1.2 (95% CI = 0.8 to 2.0), respectively, for those with normal cytology in aspirates. Compared with women from whom no fluid was obtained, incidences and adjusted RRs for women in group 1 with epithelial hyperplasia and atypical hyperplasia in aspirates were 10.8% (52 of 483), with RR = 2.4 (95% CI = 1.6 to 3.7), and 13.8% (12 of 87), with RR = 2.8 (95% CI = 1.5 to 5.5), respectively, while those for women in group 2 were 5.5% (25 of 457) and 0% (0 of 22), respectively, with a combined RR = 2.0 (95% CI = 1.3 to 3.3).
Conclusion: The results obtained with the newly followed women independently confirmed previous findings that women with abnormal cytology in nipple aspirates of breast fluid have an increased risk of breast cancer.