Ibrance Is Well Tolerated in African American Patients With Advanced Breast Cancer and Benign Ethnic Neutropenia

African American women with benign ethnic neutropenia had clinical benefit with Ibrance (palbociclib) in combination with endocrine therapy to treat advanced breast cancer.

Ibrance (palbociclib) was well-tolerated in African American women with HR-positive/HER2-negative advanced breast cancer who developed benign ethnic neutropenia, according to findings published in Cancer

CDK4/6 inhibitors like Ibrance that are approved to treat HR-positive/HER2-negative advanced breast cancer are associated with blood-related side effects, which can be neutropenia, anemia, leukopenia, lymphopenia and/or thrombocytopenia.

“African American women, who are underrepresented in CDK4/6 inhibitor clinical trials, may experience worse neutropenia because of benign ethnic neutropenia,” the authors wrote.

Benign ethnic neutropenia is a condition observed in patients of African descent in which there is a reduced absolute neutrophil count.

In the PALINA study, the researchers gave African American women with HR-positive/HER2-negative advanced breast cancer 125 mg of Ibrance daily (for 21 days on and seven days off) plus endocrine therapy. The women also had a baseline absolute neutrophil count of greater than or equal to 1000mm3. The researchers also used an analysis to assess whether patients had a Duffy antigen, which is a protein that can make individuals more resistant to developing malaria. The antigen is more common in people of African descent.

There were 35 patients who received one or more doses of Ibrance plus endocrine therapy, 19 of which had a Duffy null variant. None reported febrile (feverish) neutropenia or permanent discontinuation due to neutropenia. More patients who had the Duffy null variant (72.2%) had grade 3 or 4 neutropenia and required an Ibrance dose reduction, as opposed to those with the wild-type variant (23.1%).

The patients with the Duffy null also had lower overall relative dose intensity as well as lower clinical benefit rate (66.7%) than those with the wild-type variant (84.6%).

“These findings suggest that (Ibrance) palbociclib is well tolerated in African American women with HR-positive/HER2-negative (advanced breast cancer),” the authors concluded. “Duffy null status may affect the incidence of grade 3 neutropenia, dose intensity and possibly clinical benefit.”

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