Trastuzumab emtansine (TDM1) and trastuzumab deruxtecan (TDXd), agents that target the human epidermal growth factor receptor 2 (HER2) receptor to fight breast cancer, commonly cause thrombocytopenia. A study presented at the 2022 American Society of Clinical Oncology (ASCO) Annual Meeting explored whether this toxicity often leads to dose adjustments among people with Asian ancestry.
Researchers conducted a retrospective review to identify female patients with HER2-positive breast cancer who started therapy with TDM1 or TDXd between January 16, 2017, and October 26, 2021. Of the patients identified, 181 were eligible, with a mean age of 55.1 years. Of the study sample, 48 patients (26.5%) identified as Asian, and 124 (68.5) had metastatic breast cancer.
Thirty-three patients started therapy with TDXd exclusively; 148 received TDM1, and 45 of those patients later switched to TDXd because they developed thrombocytopenia. That resulted in 226 observations with a total of 2,551 cycles of treatment.
In total, 32 patients adjusted dosage because of thrombocytopenia. Another 112 discontinued treatment because they experienced another toxicity or because disease progressed. Twenty-seven patients in the sample completed treatment.
When the researchers compared risk of dose adjustment between Asian and Caucasian patients, they found that Asian patients has a higher risk. This was true even when the researchers took into account age, metastatic disease, and specific drug type.
“Upon confirmation in additional individuals with HER2+ cancers of the breast and other sites, this heightened susceptibility to thrombocytopenia among Asian individuals should be further investigated to elucidate the underlying mechanism and optimize clinical guidelines for prevention and management,” wrote the authors, led by Michael Rainone, of City of Hope in Duarte, California.