After a steady increase of invasive breast cancer cases in Spanish women during the 1980s and 1990s, incidence rates abruptly declined starting in 2001 a trend most likely explained by a period effect linked to screening saturation, according to a new study published online October 26 in the Journal of the National Cancer Institute.
Marina Pollan, M.D., Ph.D., of the Centro Nacional de Epidemiologia, Instituto de Salud Carlos III in Madrid, and colleagues identified invasive breast cancer cases from population-based cancer registries in Spain that had at least 10 years of uninterrupted registration over the period. The researchers took into account the starting year of the corresponding breast cancer screening program for the population and the year in which the screening program achieved full coverage of the target population.
Overall incidence rates rose by 2.9% annually during the 1980s and 1990s, but there was a statistically significant change in this trend in 2001, when incidence declined annually by 3.0%. There was a steady increase in incidence for women younger than 45 years, an abrupt downturn in 2001 for women aged 45 years, and a gradual leveling off in 1995 for women aged 65 years or older.
The sharp decline could be a result of the introduction of screening programs, according to the authors. When screening programs are introduced, cancer incidence can rise because diagnoses occur earlier than they would have without screening. But this rise is temporary.
"Once the program is in place and screening coverage of the target population reaches a plateau, incidence rates tend to decrease because the pool of undiagnosed prevalent cases has been reduced," the authors write. "We found that the change point in breast cancer incidence in Spain occurred in 2001, but this overall trend is likely to be the consequence of changes acting on different age groups and regions at different times."