In this graph, which covers the years 1975 to 2007, the top line of bars (blue) represent the incidence of breast cancers (including invasive and non-invasice lesions). The next lower line of bars (maroon) is the incidence of the invasive breast cancers (the kind that account for breast cancer deaths), and the bottom line of bars represents the rate of precancers (ductal carcinoma in situ) collected by SEER.
As you recall from the previous blog , the big drop in cancer death rates did not occur until about 1990, well after there was a rise in the number of diagosed breast precancers.
Why didn't the precancers diagnosed in the 1980s produce an immediate drop in the rate of breast cancer deaths or in the incidence of invasive cancers?
Precancer treatment works like a time machine. When you cure a precancer today, you don't see a reduction in the number of cancers that would arise that same day. You see a reduction in the number of cancers that will arise in some future date (if the precancer had been allowed to develop into a cancer, over time).
If a precancer would ordinarily require 5 years to develop invasive features (i.e., become a cancer), and you diagnose and treat the precancer in 2010, then you will eliminate a cancer that would have occurred in 2015. This explains the delay in the decrease in cancer mortality that you can always expect to see with successful precancer treatment initiatives.
- © 2010 Jules Berman
key words: precancer, precancerous, dcis, ductal carcinoma in situ, breast cancer, breast cancer mortality, cancer prevention, carcinogenesis
