For staging of breast cancer see http://www.breastcancer.org/dia_pict_staging_pf.html

Relative survival rates are calculated for Norwegian women diagnosed in the period 1992-96 ( based on approximately 10 000 cancer diagnosis).

The idea that early diagnosis is beneficial is based on common assumptions including:

breast cancer at stage I never regress,
with time an increasing proportion of stage I cancers progress to a more advanced stage leading to clinical symptoms.

From these assumptions one may deduce that early diagnosis (by screening) will lead to an incidence increase for stage I disease and an incidence decline for stage II-IV disease.