A Multicenter, Randomized, Double-blind, Phase II Study to Evaluate the Tolerability of an Induction Dose Escalation of Everolimus in Patients With Metastatic Breast Cancer

The BOLERO-2 study demonstrated an enormous benefit for patients who received everolimus in addition to exemestane in patients who progressed during/after a non steroidal (NSAI), which led to approval of everolimus in this indication. However, experience from routine use report a high rate of intolerability of this innovative treatment approach especially during the first 12 weeks of treatment. Most common side effect is mucositis/Mucositis which is considered the leading cause for treatment discontinuation not related to tumor progression.

This outside clinical trial experience is contrary to findings from BOLERO-2, where the number of patients still taking full-dose (10mg) of everolimus at 4, 8, and 12 weeks is 77.8%, 75.6%, and 75.6%, respectively. These findings are in concordance with non-interventional studies. However, findings might be biased by positive pre-selection.

In the non-responder part (setting III) of the neoadjuvant GeparQuinto study, everolimus was given as salvage treatment in combination with paclitaxel for patients without response to 4 cycles epirubicin/cyclophosphamide +/- bevacizumab. A dose-escalation schema was successfully used to improve tolerability of everolimus together with the cytotoxic agent. In fact the addition of everolimus to paclitaxel led only to increases of grades 1-4 leukopenia, grades 1-2 thrombocytopenia, leukopenia, skin changes and hyperlipidemia. Grades 3-4 hematological and nonhematological toxic effects were infrequent with no differences between treatment arms.

Moreover, Ravaud et al performed a metaanalysis of clinical trials in order to evaluate the potential relationship between everolimus exposure, safety and efficacy. Previous studies have shown that maximum everolimus concentrations are reached 1-2 hours after administering 5-70 mg oral doses, maximum everolimus concentrations increase in a dose-proportional manner between 5 mg and 10 mg and that continuous 5-10 mg once-daily dosing enables steady state to be achieved within 1 week.

The metaanalysis shows that a two-fold increase in the minimum concentration of everolimus increased the probability of tumor size reduction (odds ratio 1.4), which was associated with a trend for reduced risk of PFS events (risk ratio [RR] 0.9), but with an increased risk of grade 3 pulmonary toxicity (RR1.93), Mucositis (RR 1.49), and metabolic toxicity (RR 1.3).