HER2 positive for DCIS, HER2 neg for IDC

avanarsmom

Hi! I was recently diagnosed with Invasive Ductal CA tumor size 2.2cm associated with extensive DCIS cribriform and comedo type. Underwent MRM. Scheduled for chemo this January. ER neg, PR neg in all tumor cells present. However, HER2 positive in 80% cells seen intensity 2+ in DCIS only, not in IDC.

Is Herceptin still needed?

Beesie

Herceptin is not approved for DCIS so I think the answer is "no".

Although I haven't heard of a situation like yours before, I suspect it's not unusual.  Normally if someone presents with both IDC and DCIS, only the IDC is tested for HER2 status so it wouldn't be known if there is a difference in HER2 status between the IDC and the DCIS.  But what is known is that a large percent of cases of DCIS is HER2+ (I've seen reports indicating anything from 40% to 60%), but only approx. 20% of IDC is HER2+.  Since 80% - 90% of IDC develops from DCIS, this means that something happens that changes the HER2 status from positive to negative in a large number of cases.  I haven't read anything yet that suggests that doctors or scientists know what it is that happens, but it's for this reason that DCIS that is HER2+ isn't treated any differently than DCIS that is HER2- whereas HER2+ IDC is of course treated very differently than HER2- IDC.

avanarsmom

Thanks very much beesie! It's a sensible explanation. I asked the pathologist to review the slides again to confirm.

God bless!