In a study led by Lilu Ding and Truuske de Bock of the University Medical Center Groningen, a validated micro-simulation model was applied to evaluate the overdiagnosis of invasive breast cancer. The follow-up time of screening varied from 2 to 15 years and the screening start age varied from 50 to 68 years.
 
The researchers found that the chance of overdiagnosis of invasive breast cancer is less than 1 in 1000 when screened every two years until 69 years. Overdiagnosis decreased with longer follow-up time and stabilised at 10 years. Overdiagnosis for women at age 68 was nearly three times higher than at age 50.
 
Earlier studies found up to 54% overdiagnosis of invasive breast cancer, without distinction to age. We show that these high estimates are mainly due to a very short follow-up time. Our results show that an accurate estimate of overdiagnosis requires at least 10 years of follow-up. Moreover, the risk of overdiagnosis is larger for older than for younger women.
 
The researchers published the results of their study in the European Journal of Cancer:
Overdiagnosis of invasive breast cancer in population-based breast cancer screening: A short- and long-term perspective - ScienceDirect