A case for routine evaluation of HER2 expression in ductal carcinoma in situ

A new editorial paper was published in Oncoscience and is titled "HER2 expression should be routinely evaluated in DCIS to avoid under or overtreatment!"

HER2 is more frequently overexpressed in ductal carcinoma in situ (DCIS) than in invasive breast cancer. However, unlike invasive cancer, HER2 is not routinely evaluated in DCIS. In this new editorial, researchers Nidhi Garg and Mangesh A. Thorat from Guy's and St Thomas' NHS Foundation Trust, Wolfson Institute of Population Health, Queen Mary University of London, and King's College London discussed their recent study, which they claim is the largest biomarker study in a DCIS randomized trial.

"Prior to our study, just about a third of studies (10 of 27) investigating the association between HER2 overexpression and recurrence risk reported a significant association," note the researchers.

They showed that HER2 overexpression was associated with a 2-fold higher ipsilateral breast event (IBE) risk mediated through almost 3-fold higher ipsilateral in situ event (DCISIBE) risk [Hazard ratio (HR) = 2.90; 95% CI, 1.91–4.40; p < 0.0001]. However, HER2 overexpression was also associated with a greater radiotherapy benefit. Adjuvant radiotherapy reduced ipsilateral in situ events by 84% in HER2-positive DCIS as compared with 42% reduction in HER2-negative DCIS (Pheterogeneity = 0.04). Ipsilateral invasive event (I-IBE) risk, although higher [HR = 1.40; 95% CI, 0.81–2.42; P = 0.23], was not significantly elevated in HER2-positive DCIS.

"In this comment, we discuss the significance and clinical implications of these results. We also hope to convince the reader that more robust data are unlikely to be available for a foreseeable future and therefore clinical practice needs to change based on these results and start routinely evaluating HER2 to prevent under or overtreatment of DCIS patients," state the researchers.