Can post-lumpectomy radiation be omitted for ER/PR(+) low-volume (2 mm) low-int DCIS, with > 2 mm margins in a post-menopausal patient who will be taking tamoxifen?

This is an individualized decision weighing the benefits and potential toxicity. We know from many prospective trials that none of the clinical features mentioned sufficiently put the recurrence risk low enough (often defined as <10%) to omit radiation. However, radiation also likely will not have any survival benefit. If a postmenopausal woman is taking tamoxifen instead of AI, she may have other comorbidities or toxicity concerns that need to be taken into account as well.

Radiation for dcis used to take up to 7 weeks, but can now be completed in 3 weeks. If she chooses partial breast then it's done in 1 week. With the advancement of hypofractionated RT, I find fewer patients choosing to omit radiation altogether after a thorough discuss...

There is no prospective data on boost for DCIS - we are awaiting the results of the TROG 07.01 trial (2x2 factorial design) looking at standard- vs hypo-fractionation, and boost vs no boost. Will be presented at SABCS 12/20!

Therefore, it is up to the clinician to decide if tumor factors are significant enough to merit toxicity risks of lump bed boost, on the assumption that boost benefits in invasive breast cancer translate to DCIS. Certainly very reasonable to eliminate it.

While on the topic of DCIS, I order the DCISion RT test on every DCIS since our decision making is wrong 40% of the time. This test is the ONLY genomic platform test that I'm aware of that gives both prognostic and predictive (benefit of RT) information.