Dasatinib + Letrozole

The combination of dasatinib and letrozole is a therapeutic approach used primarily for hormone receptor-positive, HER2-negative metastatic breast cancer. This combination pairs a tyrosine kinase inhibitor (dasatinib) with an aromatase inhibitor (letrozole) to potentially overcome or delay endocrine therapy resistance. ## Efficacy and Clinical Outcomes In a randomized phase II clinical trial, the combination of dasatinib and letrozole demonstrated promising results compared to letrozole alone: - The clinical benefit rate (CBR) with letrozole + dasatinib was 71% (95% CI 58–83%), exceeding the projected CBR of 56%[1] - Median progression-free survival (PFS) with the combination was 20.1 months compared to 9.9 months with letrozole alone[1][5] - The combination essentially doubled the PFS compared to letrozole monotherapy[2][3] - Four patients remained on the combination therapy for more than 3 years[1] ## Safety Profile The combination treatment was generally well tolerated: - Most adverse events were grade 1/2[1] - The most frequent adverse events included fatigue (42.1%), nausea (38.6%), rash (26.3%), anemia (24.6%), and neutropenia (22.8%)[1] - Grade 3 adverse events were uncommon, including rash, edema, fatigue, anemia, neutropenia, arthralgia, and pleural effusion[1] - One patient experienced grade 4 respiratory failure and acute renal failure, both of which resolved[1] - Pleural effusion occurred in 9 patients (16%), mostly grade 1 or 2[1] - No grade 3/4 liver dysfunction was observed[1] - 26% of patients required dasatinib dose reductions[1] - 17.5% of patients on the combination and 9.5% on letrozole alone discontinued treatment due to adverse events[1] ## Mechanism of Action The rationale for this combination is based on preclinical evidence: - Dasatinib inhibits the Src protein, which has been implicated in breast cancer metastasis to bones[5] - In preclinical models of tamoxifen-resistant breast cancer, dasatinib alone or in combination with tamoxifen or letrozole inhibited tumor growth[1] - The combination may delay the development of endocrine therapy resistance in hormone receptor-positive breast cancer[1] ## Development Status This combination has been evaluated in a phase II clinical trial for hormone receptor-positive, HER2-negative metastatic breast cancer. While the results were encouraging, particularly the doubling of progression-free survival, researchers noted that a biomarker to measure Src activity in breast tumors would be beneficial to better determine which patients would most likely benefit from adding dasatinib to letrozole[5]. The combination may be particularly valuable for preventing or delaying acquired resistance to aromatase inhibitor therapy, suggesting its potential role in combination therapies for solid tumors[1][7].