Pfizer's Tukysa added to maintenance therapy significantly delayed disease progression in patients with HER2-positive metastatic breast cancer who had responded well to initial treatment, according to results of a late-stage trial.
Tukysa, known chemically as tucatinib, belongs to a drug class known as tyrosine kinase inhibitors that block the HER2 protein on cancer cells, helping to slow or stop tumor growth.
The drug is already approved for use in colorectal cancer and for later-stage breast cancer.
The 654 patients in the trial, all with HER2-positive advanced breast cancer at diagnosis, had already completed treatment with chemotherapy plus Roche's antibody drugs Herceptin (trastuzumab) and Perjeta (pertuzumab), without disease progression.
All of them transitioned to maintenance therapy with Herceptin and Perjeta and were randomly assigned to also receive either Tukysa or a placebo.
At a median follow-up of 23 months, the patients who received Tukysa had gone over two years without the disease worsening, known as progression-free survival. That was an improvement of 8.6 months compared with the patients in the placebo group, according to data presented at the San Antonio Breast Cancer Symposium and published in the Journal of Clinical Oncology.
Currently, most patients experience disease progression within two years of starting treatment and must resume chemotherapy, the researchers said.
Patients whose cancers were hormone receptor (HR) negative – that is, their tumor cells did not have proteins that bind to specific hormones - had a 44.6% reduction in risk of progression or death, with a 12.3-month improvement in median PFS.
Those with HR-positive cancer cells had a 27.5% reduction in risk of progression or death and a 6.9-month improvement in median PFS.
The findings emphasize the importance of enhancing HER2 targeting during the maintenance phase, study leader Dr. Erika Hamilton of the Sarah Cannon Research Institute in Nashville said in a statement.
"Prolonging the maintenance phase allows patients to maintain disease control, while extending their time off chemotherapy," she said.
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