Variation in net survival and in the excess mortality hazard for breast cancer according to stage and age at diagnosis.

BACKGROUND: In France, survival in the general population of women with breast cancer, according to stage at diagnosis has been poorly studied. The objective of this study was to estimate net survival and the excess mortality hazard (EMH) over time for breast cancer according to stage and age at diagnosis. METHODS: A representative sample of women diagnosed with invasive breast cancer between 2009 and 2015 was drawn from French cancer registries. Stage at diagnosis was defined using TNM classification. Net survival was estimated for each stage using the Pohar-Perme estimator. Excess mortality hazard were modeled using penalized flexible models as a function of time since diagnosis, age and stage. RESULTS: Among 9628 women identified, 47% were diagnosed at stage I and 7% at stage IV. Net survival decreased as stage increased. For stage IV, the EMH was highest in the first year after diagnosis compared to other stages. For stage II, however, the EMH increased until around three years after diagnosis and then decreased, while it reached a plateau for stage III. For stage I, EMH remained very low throughout follow-up. At five years of follow-up, older women had higher EMH across all stages. For stages I and II, younger women (aged 40) had higher EMH than women aged 50-60. CONCLUSION: This study provides updated population-based estimates of net survival and EMH over the five years following breast cancer diagnosis in France. Analyzing EMH allows us to better describe prognosis over time and to adapt the follow-up of women according to the stage at diagnosis.