Tamoxifen reduces cancer by 40%?

moskitoe

My mother age 72, was recently diagnosed with stage 0 DICU and will have a lumpectomy followed by radiation. She is hesitant to take the 5 year tamoxifen treatment suggested to her by her doctors. This community has been great and you shared with me encouraging data that with lumpectomy and radiation, a chance of recurrence goes down to below 15%. However, her oncologist shared data that tamoxifen reduces the cancer risk by 40%. Where is that data from? Does anyone know where this number is from? I'm having trouble understanding this data and how it fits with the first set of data reducing the risk to less than 15% with lumpectomy and radiation. Thank you.

Annette47

The average reduction in risk is 40%, which is not 40% overall, but 40% of the remaining risk, so 40% of the 15% that is left after lumpectomy and radiation, so on average the risk after lumpectomy, radiation, and tamoxifen would be about 11%. Those are averages though - each case is different.

BarredOwl

Hi moskitoe:

It sounds like your mother has not yet had her lumpectomy. Therefore, her risk of recurrence (loco-regional and distant) following lumpectomy and radiation cannot be accurately ascertained at this time.

As I noted in your other thread, you are putting the cart before the horse. Your mother cannot make informed decisions about the potential benefit of systemic treatment (e.g., tamoxifen) until after her surgery. This is because the results of the surgical pathology may affect understanding of her recurrence risk.

Despite her current diagnosis of intermediate grade DCIS based on biopsy, that may not be her final diagnosis. According to the American Society of Clinical Oncologists ("ASCO"), among patients with apparently pure DCIS by minimally-invasive biopsy (e.g., core-needle, invasive disease is found "10% to 20% of cases overall, approximately half of which are limited to micro invasive cancer" ("T1mi", where Tumor ≤ 1 mm in greatest dimension).

(As an example of this, I was diagnosed with DCIS on both sides. However, the surgical pathology on my right side found a 1.5 mm IDC, plus a few areas of microinvasion. On the left, the extent of the DCIS was much greater than appreciated from either mammography or MRI.)

As you will appreciate, invasive breast cancer can have a different recurrence risk as compared with pure DCIS, and leads to consideration of distant recurrence risk in treatment decisions.

Even if no invasive disease is found, the grade, extent, and/or architecture of the DCIS may differ in material ways from what biopsy shows and this may alter understanding of local recurrence risk. The size of the surgical margins is also a factor.

Please understand that this forum is not an appropriate source of information regarding your mother's baseline recurrence risk or her residual risk after lumpectomy plus radiation:

(1) After her surgical pathology is available, please seek expert professional medical advice from a Radiation Oncologist ("RO") about her residual local recurrence risk after lumpectomy plus radiation.

(2) Then, with that information in hand, please seek expert professional medical advice from a Medical Oncologist ("MO") about by how much tamoxifen can potentially reduce that risk. Request an explanation of how that information is derived.

Unfortunately, members of this community often provide inaccurate information. Therefore, all information you get here (including from me) should be verified with your mom's medical oncologist and radiation oncologist to ensure she receives accurate, current, case-specific expert professional medical advice regarding her risk of recurrence and the potential benefits of treatment.

Informed decisions should be based on case-specific expert professional medical advice.

BarredOwl

BarredOwl

Hi Annette47:

As I just noted, until the surgical pathology is available and an expert Radiation Oncologist provides information about her residual recurrence risk following radiation (which may depend on the radiation regimen received), it is premature for moskitoe to be trying to estimate the potential risk reduction benefit of adding tamoxifen.

In general, I have often seen the relative risk reduction benefit of tamoxifen given as approximately 45% (not 40%). Therefore, in due course, moskitoe should obtain advice from the MO regarding the actual relative risk reduction benefit.

Whatever the actual risk reduction benefit is, as you note, it is an average based on the results of clinical trials comparing recurrence rates between groups, specifically between a group that received tamoxifen and a group that did not.

By the way, assuming a relative risk reduction benefit of 40% (which requires confirmation), then assuming a residual local recurrence risk of 15% after lumpectomy plus radiation, the absolute risk reduction benefit would be 6%, leaving an estimated residual risk of 9% by my math:

15% x 0.40 = 6% (absolute risk reduction benefit)

15% - 6% = 9% (residual risk with addition of a drug that achieves a 40% risk reduction)

Again, at this time, prior to surgery, the estimate of 15% is not a credible estimate, and the risk reduction benefit is often recited as ~45% (and should be confirmed).

BarredOwl

Annette47

Hi Barred Owl -

You are absolutely correct ... it should be 9. I somehow subtracted 6 from 15 and got 11. No idea how, LOL. I do agree it is premature to be estimating risk prior to surgery and did specify that we were talking about averages, and that individual cases may vary. Her question though was about what an average risk reduction of 40% would mean in the context of lumpectomy and radiation having brought it down already, and the clarification of relative risk vs. absolute risk in a generic sense would be useful prior to being given exact numbers.

For what it’s worth, 40 was the average number given to me by my team as well, but as you say, what really matters is the risk to a particular individual.

BarredOwl

It may be that relative risk reduction benefit may lie somewhere in the middle of 40 to 45%.

BarredOwl