DCIS question for the experts

Not an expert, but I have read that DCIS is much more likely to be HER2+ than is IDC. To my understanding, it's not that (as your Nurse Navigator said) that all DCIS would test positive, but the chances of DCIS testing positive are much higher than the prevalence of HER2+ invasive cancer. At this point, the significance of HER2+ in DCIS is unknown - it doesn't seem to make it more aggressive like it does with invasive cancer, and is not known to make the DCIS more likely to turn invasive.

Because of this (the HER2+ not seeming to make a difference) many places do not bother to test DCIS for HER2 as it wouldn't change the treatment or prognosis. My DCIS was not tested, and my invasive component was too small to test (small enough it wouldn’t have generated a treatment change even if it was HER2+). I think that many oncologists who are used to dealing with invasive cancer, don’t always know much about DCIS, and may not be aware of how prevalent HER2+ DCIS really is. I found that my radiation oncologist seemed to have a much better understanding of DCIS than my medical oncologist.

Mommyathome if your cancer is HER2+ it would make a difference. Read here

https://community.breastcancer.org/forum/80/topics/738946?page=

Doctors that don't want to test make me very nervous......

Hi Mayk:

I am not an expert, but note the following.

Please note that the abstract in the thread linked by Marijen ("Does hormone receptor (HR) positivity affect the prognosis in breast cancers with human epidermal growth factor receptor 2 (HER2) overexpression?") appears to relate to invasive disease, and is not relevant to your questions regarding pure DCIS. For example, the patient group includes patients who received chemotherapy (never indicated for pure DCIS) and some node-positive patients, indicating they had invasive disease.

I agree that pure DCIS can sometimes be HER2 negative.

According to background information from a 2015 article (citations omitted, emphasis added), in contrast with invasive disease, the ". . .prognostic significance of HER2 status in DCIS is, however, less clear. Both the relation of HER2 to risk of recurrence and its role in the progression from in situ to invasive cancer have been debated. HER2 over-expression is reported to be more frequent in DCIS than in invasive cancer."

Regarding HER2 testing practices in pure DCIS, in general, the National Comprehensive Cancer Network (NCCN) guidelines for Breast Cancer (Version 1.2016) do not recommend routine assessment of HER2 for pure DCIS. This appears to reflect the current level of evidence regarding value as a prognostic marker in pure DCIS (unclear, weak), and that HER2-targeted treatments are not used in the pure DCIS setting (emphasis added):

"Although HER2 status is of prognostic significance in invasive cancer, its importance in DCIS has not been elucidated. To date, studies have either found unclear or weak evidence of HER2 status as a prognostic indicator in DCIS.(41-44) The NCCN Panel concluded that knowing the HER2 status of DCIS does not alter the management strategy and routinely should not be determined."

In accordance with the current treatment guideline, many patients with pure DCIS do not receive HER2 testing.

This might or might not change in the future, since it is an on-going area of research, and we may learn more from new studies about the prognostic implications of differing ER, PR and HER2 statuses in pure DCIS.

Your oncologist's remark refers to your entire status, including ER and PR negativity, so endocrine therapy is not being offered, which may factor in to her view of your particular case.

BarredOwl

I too was never tested for HER2. I was diagnosed with DCIS in SITU, ER positive, stage 0 June 29th, 2015. BMX, nipple sparing on September 18th, 2015. exchange surgery Dec. 15th. My onco says there is no need for tamoxifen because I am post menopausal. I would love to hear from others with a similar situation. Also, how would you start a new discussion on here asking a similar question?