All DCIS her2+?

No.

About 40% - 60% of DCIS cases are HER2+, vs. about 15% - 20% of IDC cases.

Most often DCIS isn't tested for HER2. This is because HER2 status doesn't appear to affect DCIS. There have been lots of studies, and while a few do suggest that HER2+ DCIS may be more aggressive, a few actually show the opposite, that HER2+ DCIS may be less aggressive. And most of the studies show no difference in prognosis whether the DCIS is HER2+ or HER2-. Because there is no difference in prognosis, there is also no difference in treatment for DCIS whether it's HER2+ or HER2-. Therefore HER2 testing is unnecessary; it provides information that adds nothing to the diagnosis, prognosis or treatment plan. It is unactionable information.

This is very different from invasive cancer, where it is well established that HER2+ invasive cancers are very aggressive and without adequate treatment, have a less favorable prognosis. Herceptin, combined with chemo, has been a game-changer for HER2+ invasive cancers, bringing survival rates right in line with much less aggressive breast cancers.

While over the years there have been a couple of very small, limited-use trials of Herceptin on DCIS patients, Herceptin is not approved for DCIS.