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** May 5, 2011 12:16PM**
- edited
May 5, 2011 12:20PM
by
otter

DesignerMom, it's the math. I don't know what your oncos told you, so I'm just going to work with the numbers you used in your post.

Okay, so let's assume that taking tamoxifen or an AI will decrease the risk of recurrence by 50% (that is, cut the risk in half). I know the AI's are supposed to work slightly better than tamoxifen, but let's keep things simple for these examples.

If someone is told her recurrence risk will be, say, 6% if she does not take tamoxifen or an AI, and tamoxifen or AI cuts that risk by 1/2 (50%), then her risk will be 3% if she takes the tamoxifen or the AI. [6% x 0.50 = 3%] So far, so good, yes? (That's the example you used.)

That means if someone has a recurrence risk of 20% without tamoxifen or an AI, then taking the tamoxifen or an AI would bring her recurrence risk down to 10%. [20% x 0.50 = 10%] Similarly, a 30% risk of recurrence without the tamoxifen or AI would be decreased to 15% with the tamoxifen or AI. (Note that we're multiplying the risk by the risk-reduction factor; we're not subtracting the risk-reduction factor.)

Now, let's look at it the other way around, using your own example: "As my Oncotype score was 16 my chances of recurrence was 10% if I take AIs. I was told without AIs my added risk was about 5% (50% of the 10%) , added to the10% = 15%, not 20%."

That can't be true, unless our assumption about the 50% risk reduction with tamoxifen or AI's is incorrect. Check the calcuation: If your risk without the AI's really was 15%, then with the AI's it would be just 7.5%, not the 10% indicated by the Oncotype score. So, something's wrong with the math.

The formula for figuring your risk without tamoxifen or an AI is this (assuming the 50% benefit is correct): 10% = 0.50 x "N" (then solve for "N")

Okay: If someone was told her risk of a recurrence was 3% after taking tamoxifen or an AI, what would it be if she did not take the tamoxifen or AI? It would have to be 6%, which is *twice* (2x) the risk it would have been *with* the estrogen-suppressing/blocking drugs. That's basically because the inverse of 1/2 is 2. [3% = 0.5 x "N" and then solve for "N"]

If the drugs cut the risk in half (i.e., reduce the risk by 50%), then not taking the drugs will double the risk....not increase it by 50%.

Unfortunately, I never was any good at explaining math problems.... It seems I'm much better at yelling and waving my arms. <sigh>

otter

**Dx**
2008, IDC, Stage IA, Grade 2, 0/3 nodes, ER+/PR-, HER2-