Are prognostic factors more favorable for breast cancer detected by organized screening than by opportunistic screening or clinical diagnosis? A study in Loire-Atlantique (France).

PURPOSE: Comparisons of breast cancer characteristics between organized and opportunistic screening have been limited. This study was designed to compare characteristics of cancers detected by either organized or opportunistic screening as well as clinically diagnosed cancers in Loire-Atlantique (a French administrative entity), from 2003 to 2007.
METHODS: This study is based on data from the population-based Loire-Atlantique Cancer Registry. Stage at diagnosis and prognostic characteristics of carcinomas detected by organized screening were compared, by age-adjusted logistic regressions, to those of cancers detected by opportunistic screening and diagnosed clinically. Analyses were restricted to women aged 50-74 years (the age group targeted by the organized screening program) for the 2003-2007 period.
RESULTS: Between 2003 and 2007, 2864 invasive and 400 in situ breast cancer cases were diagnosed in women aged 50-74 years in Loire-Atlantique. Compared to cancers diagnosed clinically, cancers detected by organized screening were more likely to be in situ (13.7% vs. 3.8%), diagnosed at an early stage (74.4% vs. 51.3%), have a low SBR grade (grade 1: 35.4% vs. 18.5%), and be positive for estrogen-progesterone receptors (68.3% vs. 59.0%). The distribution of stage at diagnosis and prognostic characteristics between organized and opportunistic screening were similar.
CONCLUSION: These findings are consistent with the hypothesis that breast cancers are detected early by organized screening. Cancer characteristics were similar between the two screening modes. Estimating the impact of mammography screening on mortality in Loire-Atlantique should be the object of further investigations.