We considered the risk of subsequent invasive breast cancer in a population-based series of 579 carcinomas in situ (CIS) of the breast (482 ductal, 88 lobular) registered between 1977 and 2002 in the Swiss Canton of Vaud. A total of 55 cases of invasive breast cancer were observed vs. 12.3 expected, corresponding to a standardized incidence ratio (SIR) of 4.5 (95% confidence interval [CI], 3.4-5.8). The SIR was 4.6 after ductal and 4.2 after lobular CIS, was similar with passing time since CIS diagnosis, but was higher (SIR = 5.5) for women aged <55 years. At 20 years following CIS, the cumulative risk of invasive breast cancer was 26%, similar for lobular and for ductal CIS. The incidence of invasive breast cancer following CIS showed no consistent pattern of trends with age, all rates in subsequent age groups ranging between 10 and 18 in 1,000. This is compatible with the occurrence of a single mutational event in a population of susceptible women. ' 2005 Wiley-Liss, Inc.Key words: breast neoplasms; cancer registry; ductal carcinoma in situ; lobular carcinoma in situ; noninvasive breast neoplasms; second primary Carcinoma in situ (CIS) of the breast is a preinvasive breast tumor that has become increasingly commonly detected in women undergoing (screening) mammography. [1][2][3] In recent years, CIS accounted for over 20% of breast cancers diagnosed in the United States (i.e., over 50,000 cases per year) 1,4 and Europe. 5,6 Substantial upward trends were observed earlier for ductal CIS (DCIS) 7 and, more recently, for lobular CIS (LCIS).
5,6The prognosis of women diagnosed with breast CIS is also poorly defined.2 In large clinical trials from the United States [8][9][10][11] and Europe, 12-15 the risk of ipsilateral invasive breast cancer varied between 14 and 32% according to length of follow-up and type of therapy, and that of contralateral breast cancer varied between 2 and 6.6%.Scanty population-based data are available. Among them, in a series of 28 noncomedo DCIS from the United States, 16 the risk of invasive breast cancer was elevated up to 30 years after diagnosis. Among 1,929 women with DCIS and 282 with LCIS from western Washington state, the risk of contralateral invasive disease was about 2-fold after DCIS and 3-fold after LCIS. 17 In the U.S. Surveillance, Epidemiology and End Results (SEER) Program, 1,525 DCIS in women 40 and older were diagnosed between 1978 and 1983 (before screening mammography was common), and 5,547 between 1984 and 1989 (when screening mammography became common). No information on incidence of subsequent invasive breast cancer was available, but the relative risks (RR) of breast cancer death were 3.4 in the first period and 1.9 in the second one.18 Another series of 3,455 CIS cases from Sweden, including 116 cases of invasive cancer, gave an RR of 4.5 for DCIS and of 4.0 for LCIS. 15 A series of 4,198 women diagnosed with CIS between 1975 and 1998 in the Connecticut Tumor Registry showed a 10-year cumulative probability of contralateral breast cancer (invasive and CIS) of ...