To describe temporal trends in the incidence of carcinoma in situ of the breast in New South Wales, Australia, between 1972 and 2009.
Observational study of women who received a diagnosis of ductal carcinoma in situ (DCIS) or lobular carcinoma in situ (LCIS) from 1972 to 2009 in the New South Wales Cancer Registry database.
Among 8,721 women with DCIS, the median (range) age at diagnosis was 57 (21-97) years. DCIS incidence rose from a mean of 0.2 per 100,000 during 1972–1983 to 16.0 per 100,000 over 2005-2009, an 80-fold increase. Incidence increased across all ages, but more so in the target screening mammography group (50-69 years). Women aged 50-69 years comprised 56.8% of DCIS cases and had the highest recorded incidence of 46.6 per 100,000 during 1996-2009. DCIS as a proportion of all breast cancer was, on average, 0.4% during the pre-screening period 1972-1987, and increased to 12.0% after the establishment of screening (1996-2009). From 1985-2004, DCIS rates rose continually among all women. Since 2005, incidence increased in women aged 50-69 years, but stabilised in younger women and decreased in older women. Among 778 women with LCIS, the median (range) age at diagnosis was 52 (28-86) years. LCIS incidence rose from 0.2 per 100,000 during 1972-1983 to 1.6 over 2005-2009, an 8-fold increase. The magnitudes of these increases were highest among women aged 50-69 years; 4.6 per 100,000 during 1996-2009. LCIS as a proportion of all breast cancer was, on average, 0.2% during the pre-screening period (1972-1987), and 1.0% after the establishment of screening (1996-2009).
Incidence rates of DCIS and LCIS have increased over the past several decades, with the increase in DCIS much greater compared to LCIS. In women aged 50-69 years, DCIS rates have continued to rise, with an observable increase since 2005. Despite known under-recording of carcinoma in situ of the breast prior to 1992, our results show clear age differences in DCIS incidence increases associated with screening mammography.