Risk question and visit to MO

Linda, I was 49 when I was diagnosed.  My oncologist told me that my risk to develop a new BC was about double that of the average woman my age.  A that time, the risk level of the 'average 49 year old woman' was estimated to be 11%.  So that put my risk at 22%.

This 22% risk is spread over the rest of my expected lifetime - 41 years to age 90. So it works out to just over 0.54% (just over a 1/2 a percent) risk per year. However because the risk to develop BC increases as we age, I actually face more of that 22% risk when I'm older than I do now. Here's the data on risk by age:

from age 20 through age 29 . . . . . . 0.05 percent (often expressed as "1 in 2000")
from age 30 through age 39 . . . . . . 0.43 percent (often expressed as "1 in 233")
from age 40 through age 49 . . . . . . 1.45 percent (often expressed as "1 in 69")
from age 50 through age 59 . . . . . . 2.38 percent (often expressed as "1 in 42")
from age 60 through age 69 . . . . . . 3.45 percent (often expressed as "1 in 29")
from age 70 through age 89 . . . . . . 4.44 percent (often expressed as "1 in 23")

TOTAL LIFETIME RISK: 12.2 percent (often expressed as "1 in 8")

So this suggests that during the 10 years of my 50s (which I'm half way through now), my risk is 4.76%, during my 60s my risk will be 6.9% and from age 70 till 90, my risk will be 8.88%. (The total is a bit less than 11% because lifetime risk estimates have dropped from 12.8% to 12.2% in the 5 years since I was diagnosed.)  

One important thing to know about risk is that we "leave risk behind". What that means is that once we are past our 20s, 30s, 40s, etc., we don't have to worry about the risk that we faced during those years. So although my annual risk goes up as I get older, my total risk goes down. Today, at age 55, my remaining lifetime risk is now in the range of 18% - 20% (depending on whether I use my original estimates from 6 years ago or the latest risk data).  

My oncologist used "double the risk" as a rule of thumb; I've seen women here who've been told something similar, some who've been given lower numbers, and some who've been given higher numbers (3 or 4 times the risk, rather than double). It's important to also factor in any personal or family health issues that might increase one's risk.  Whatever you come up with, it's just an estimate. The truth is that it's impossible to know what any one individual's risk really is. The reason risk is thought to be higher than average is simply because we don't know what caused the BC to develop in the first place therefore we have to assume that the cause may still be a factor and might make it more likely for BC to develop again. There's not a lot of precision to that.  Having said that, a 13% risk to develop a new BC over the next 5 years seems pretty steep, no matter what assumptions one uses.

As for recurrence risk, this is a separate and completely different calculation and a separate and completely different risk.  Recurrence risk affects only the breast that had BC, and the level of risk depends on the pathology of the cancer and the surgical margins. And while a recurrence can happen even years into the future, most recurrences happen within the first 5 years and certainly within the first 10 years.  So if you start with a 4% recurrence risk, after 10 years you'll like have only a fraction of a percent risk left.  Recurrence risk and the risk to develop a new primary BC are not additive. You have an X% risk that one thing will happen, and a Y% risk than another thing will happen.  Hopefully neither happen, but it's possible that both could happen. The two risks are independent of each other.

Hope this all makes sense and helps!