HER2-Low–Positive Tumors: A New Subgroup of Breast Cancers Identified by IHC?
Posted: Thursday, November 4, 2021
According to Sibylle Loibl, MD, of the German Breast Group, Neu-Isenburg, and colleagues, HER2-low–positive tumors may represent a new subtype of breast cancer by standardized immunohistochemistry (IHC), distinct from HER2-zero tumors. The results of this pooled analysis of four clinical trials, which were published in The Lancet Oncology, provide a basis for the refinement of future diagnostic and therapeutic strategies.
“HER2-low–positive tumors have a specific biology and show differences in response to therapy and prognosis, which is particularly relevant in therapy-resistant, hormone receptor–negative tumors,” the investigators commented.
The investigators identified 2,310 patients with HER2-low–positive (47.5%; defined as IHC1-positive or IHC2-positive/in situ hybridization–negative) or HER2-zero (52.5%; defined as IHC0) primary breast cancer who were treated with neoadjuvant combination chemotherapy. A total of 64.0% and 36.7% of these tumors were hormone receptor–positive, respectively.
The pathologic complete response rate seemed to be significantly lower in patients with HER2-low–positive tumors than in those with HER2-zero tumors (P = .0002). In the hormone receptor–positive subgroup, patients with HER2-low–positive tumors also seemed to experience significantly lower pathologic complete response rates (P = .024); however, this did not appear to hold true in the hormone receptor–negative subgroup (P = .21).
Patients with HER2-low–positive tumors tended to experience significantly longer durations of survival than those with HER2-zero tumors (3-year disease-free survival: stratified log-rank P = .0084; 3-year overall survival: stratified log-rank P = .0016). Survival differences were also reported in patients with hormone receptor–negative tumors (3-year disease-free survival: stratified log-rank P = .0076; 3-year overall survival: stratified log-rank P = .016). However, according to the investigators, no statistically significant differences were observed in those with hormone receptor–positive tumors (3-year disease-free survival: stratified log-rank P = .39; 3-year overall survival: stratified log-rank P = .13).
Disclosure: For full disclosures of the study authors, visit thelancet.com.
