A new drug treatment reduces the risk of breast cancer recurrence in women who have had the initial tumor removed, according to results of a clinical trial presented at the congress of the American Society of Clinical Oncology (ASCO, for its initials in English) held in Chicago. The treatment has proven effective in the most common type of breast cancer, called HR/HER2-, which represents 70% of all cases of the disease. This type of cancer is characterized by the tumor cells having many hormone receptors (HR, in English) but few receptors for the HER2 protein.
The arrival of this new type of drug represents the most important advance in 25 years for the treatment of this tumor in cases diagnosed when there are no metastases, which are the majority. At that time, the breakthrough consisted in the introduction of aromatase inhibitors, an innovative hormonal treatment.
“These are initial but impressive data that demonstrate a significant reduction in the risk of relapse in high-risk patients. They will change clinical practice,” said Rita Nanda, from the University of Chicago, who did not participate in the study, at a press conference on Wednesday.
Approximately 30% of ER/HER2- breast cancer cases are considered high risk. Based on this estimate, around 20% of women diagnosed with breast cancer could benefit from the new treatment, which represents around 7,000 new patients a year in Spain.
According to the results presented at the Chicago congress, which with more than 40,000 participants is the most important cancer congress in the world, the drug ribociclib in the usual hormone therapy has reduced breast cancer recurrences by 25.6% during the first three years since the start of treatment.
The drug inhibits CDK4 and CDK6 enzymes, which promote cell proliferation. The first three CDK4/6 inhibitors were approved in Europe between 2016 and 2018 for the treatment of patients with metastatic ER/HER2 breast cancer, after being shown to increase survival in this population. Since then, the three drugs have also been tested in patients without diagnosed metastases.
The results presented in Chicago correspond to ribociclib from the Novartis company. In the clinical trial, which started in January 2019 and has not yet ended, 5,101 patients considered to be at high risk due to the size of the initial tumor and/or the number of lymph nodes affected by tumor cells are participating.
Spain is, after the USA, the second country with the most participants in the study, with 761 patients from 47 hospitals. After an average of three years of follow-up, 12.9% of patients who received only standard hormonal treatment after surgery experienced a recurrence of breast cancer. Among those who also received ribociclib, the figure dropped to 9.6%. The difference between the two figures is equivalent to a 25.6% risk reduction.
The most important side effect recorded among patients treated with ribociclib was neutropenia, a reduction of one type of white blood cell in the blood, which increases the risk of infections. But in general the drug is well tolerated, Dennis Slamon, an oncologist at the University of California in Los Angeles who has led the study, emphasized at the press conference.
Ribociclib thus joins Lilly’s abemaciclib, another CDK4/6 inhibitor that has shown to improve the prognosis of patients with ER/HER2- non-metastatic breast cancer. Lilly’s drug has shown efficacy in a higher-risk group of patients, while Novartis’s has shown it in a wider group, which includes women who do not have any lymph nodes affected by tumor cells. The third CDK4/6 inhibitor, Pfizer’s palbociclib, has not been shown to be effective in preventing relapses.
“There is a significant unmet need to reduce the risk of recurrence and provide a tolerable treatment option that keeps patients cancer-free without disrupting their daily lives. The Natalee study was specifically designed to address this unmet need,” says Dennis Slamon, who announced the results of the clinical trial at a press conference and presented them to Congress yesterday.
