Contralateral breast cancer in Vaud, Switzerland

The incidence of most cancers rises with the fourth to fifth power of age, and that of breast cancer rises steeply up to age of menopause and continues to rise, though more slowly, thereafter. Contralateral breast cancer, however, seems to have a completely different age incidence pattern. According to the data of the Connecticut Cancer Registry, contralateral breast cancer rate was around 1% per year in women below age 45, and decreased subsequently to approach a constant rate of approximately 0.7% per year.1 In the Swedish Family Cancer Database, including 2,529 contralateral breast cancers, the rate was 0.8–0.9% per year between age 30 and 50, and declined thereafter to approximately 0.4% per year.2 This pattern of risk is compatible with the occurrence of a single mutational event in a population of susceptible women.3, 4 To provide further information on the issue, we have examined the epidemiology of contralateral breast cancer in the Swiss Canton of Vaud. For the present analysis we used the Vaud Cancer Registry dataset, which includes incident cases of malignant neoplasms in the Canton (around 602,000 inhabitants in 1990).5 Population-based incidence data have been available since 1974. After exclusion of 166 breast cancer cases detected either at autopsy, or at death, or by death certificate alone, and of synchronous breast cancers (i.e., within 2months after the first primary, n = 242), the present series comprised 7,734 women with a first breast cancer diagnosed between 1974 and 1998 (rate of histological confirmation: 96.8 percent). These women were followed-up to the end of 1998 for the occurrence of a second contralateral primary neoplasm, emigration, or death, for a total of 49,143 person-years at risk. Among these women, 214 had subsequent contralateral breast primary. Figure 1a gives the age distribution of breast cancer in the general population, based on 7,520 first single neoplasms and no subsequent contralateral, showing the well known steep rise in incidence below age 50, and the leveling of the slope of age thereafter. Age-specific incidence of (a) first breast cancer in the general population (n = 7,520; rates in quinquennial age groups per 100,000 women); (b) contralateral breast cancer in 214 women with first breast cancer (rates in decennial age groups per 100,000 women and (c) first breast cancer in the general population in 214 women who presented with contralateral breast cancer (rates in decennial age groups per 100,000 women). Swiss Canton of Vaud, 1974–98. Figure 1b gives the incidence of contralateral breast cancer, based on 214 neoplasms. The peak rate of 800/100,000 women was reached at age 30 to 39, the rate declined and reached 500/100,000 between age 45 and 69, and further declined thereafter to 300–400/100,000, i.e. a rate similar to that of first primary neoplasms above age 70. Figure 1c gives the age distribution of rates in the general population of first breast neoplasms in the 214 women with second ones. The rate of 6/100,000 women was reached at age 40 to 49, the incidence rates tended to level off until age 70, and to decline thereafter. The present data confirm that the age incidence curve of contralateral breast cancer is substantially different from that of breast cancer in the general population, with a peak at younger age (30–39 years), a plateau between 40 and 69 years, and a decline above age 70. Consequently, the relative risk of occurrence of a contralateral breast cancer will decline with age, because the background reference incidence rises with age.6-8 This pattern of risk would be compatible with the elimination of susceptible individuals with advancing age, or with a hormone-related influence on contralateral breast cancer, which may decline with menopause.9-11 The incidence of neoplasms other than breast, however, does not seem to be elevated in women diagnosed with breast cancer in this population.12 The Vaud dataset also indicates that the incidence of first breast cancer in women with subsequent contralateral neoplasm rises steeply below age 40, reaches a plateau between 40 and 69 years, and tends to decline thereafter, i.e. the slope of the age curve is substantially different from that of women without subsequent contralateral breast cancer, again pointing to the existence of a susceptibility in this subgroup of women.3, 4 The contributions of the Vaud Cancer Registry's staff are gratefully acknowledged. Fabio Levi Fax: +4121-3230303*, Lalao Randimbison*, Van-Cong Te*, Carlo La Vecchia , * Registre vaudois des tumeurs and Unité d'épidémiologie du cancer, Institut universitaire de ḿdecine sociale et préventive, Lausanne, Switzerland, Istituto di Ricerche Farmacologiche “Mario Negri”, Milan, Italy, Istituto di Statistica Medica e Biometria, Università Degli Studi di Milano, Milan, Italy