Here is a link to the interim report from the BCIRG study presented in 2005.
http://www.bcirg.org/Internet/Studies/BCIRG+006.htm
It is difficult to give "the" answer to your question. Even if you evaluate many variables including tumor size, ER/PR/HER2 status, node involvement, etc. it is still a complicated numbers game.
Anyway, from the study above, at TWO years, the Disease Free Survival rate for chemo+herceptin is around 92%. Without herceptin, the DFS rate is 86%
At four years, the DFS rate for chemo+herceptin is between 80-84% (depending upon chemo regimen) with the non-herceptin group at 73%.
The number of deaths reported were 3.3% with chemo alone and 2.2% with chemo+herceptin (actual numbers were presented but I did the math).
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