In Geneva, breast cancer incidence in women aged <40 years has recently doubled. This increase may be partly explained by a higher screening frequency of younger women and better surveillance and recognition of familial risk factors. Improved tumour detection through advances in imaging techniques may also be involved, since in 1995–2001 less than 30% of breast cancer diagnoses in young women involved MRI compared with nearly 50% in 2002–2004 (P=0.006).
Nevertheless, these detection biases seem unlikely to explain fully the observed incidence increase. Screening and improvement in diagnostic techniques should lead to a shift in stage distribution towards earlier stages, whereas in our population, this did not change significantly, and the proportion of clinically palpable tumours remained constant. The screening programme implemented in Geneva 10 years ago targets women aged 50–69 years, and screening for breast cancer in women <40 years is rare (Lutz et al, 2000
). Furthermore, the proportion of patients reporting a positive family history has remained relatively stable around 30% between the two periods. We can also reasonably rule out an increase in fortuitous discovery of contralateral breast cancer as only two women were diagnosed with synchronous breast cancer in 2002 and 2003 respectively.
Although significant, our observation is based on only 63 patients diagnosed in 2002–2004, and should be interpreted with caution. With respect to any change in population estimates, the young resident female population grew smoothly over the study period, with no sudden increase in 2002–2004 (). Among other cancer sites of women aged 25–39 years, we found a significant increase of melanoma (mean annual increase of 6.9%; 95% CI: 0.3–13.8, P
=0.038) starting early in the study period, but this is already a well-documented phenomenon in Switzerland (Association of Swiss Cancer Registries (ASCR), 2002
Other reasons should be explored to explain this increase in breast cancer incidence in younger women. Most known breast cancer risk factors, including nulliparity or later age at first full-term pregnancy, early menarche, dietary habits, alcohol intake, and lack of physical activity, apply at all ages. However, some other factors, such as family history of breast and/or ovarian cancer, in utero
exposure, oral contraceptive use, smoking, and breast radiation are more relevant to young women (Yankaskas, 2005
; Colditz et al, 2006
In Geneva, prevalence of obesity has increased among adolescents and young females (Morabia and Costanza, 2005
), but, in contrast to post-menopausal women, it appears to be protective against breast cancer in young women (Bouchardy et al, 1990
; Magnusson et al, 2005
; Michels et al, 2006
). Smoking still seems to be increasing among women in Geneva and, compared with older women, young women begin smoking cigarettes at a much earlier age and are heavier smokers (Costanza et al, 2006
). No causal relation between breast cancer and smoking is generally accepted although any impact could be greater on young women (Miller et al, 2007
). In this study, we can exclude an association with previous cancer treatment, given that only one woman was so affected (bilateral ovarian cancer).
In comparison, for Europe and the United States, we found no recent or sudden increase in breast cancer incidence among women under 40 years in the two main public-use cancer registry data sets, the Surveillance Epidemiology and End Results (SEER) and Cancer Incidence in Five Continents (CIF) (International Agency for Research on Cancer (IARC), 2002
; National Cancer Institute (NCI), 2004
). However, the latest available years were 1997 for CIF and 2003 for SEER.
In conclusion, we observed a significant increase in young breast cancer patients. At present, we cannot definitively rule out an increased surveillance and detection bias and we cannot confidently conclude a sustained increase. Careful surveillance of recent trends of breast cancer incidence is required for young women. If other population-based cancer registries confirm this trend, further research on breast cancer risk factors, including any acting in utero and early in life, would be indicated.