Leptomeningeal Disease in EGFR-Mutated Lung Cancer: Can We Finally Define a Standard Treatment?

This podcast describes the results of the BLOOM study, evaluating the efficacy of osimertinib in EGFR-mutated lung cancer with leptomeningeal disease after failure of prior EGFR TKI therapy.

TRANSCRIPT

This JCO Podcast provides observations and commentary on the JCO article “Osimertinib In Patients With Epidermal Growth Factor Receptor Mutation-Positive Non-Small-Cell Lung Cancer and Leptomeningeal Metastases: The BLOOM Study” by Yang et al. My name is Jürgen Wolf and I am the medical director of the Center for Integrated Oncology at the University Hospital of Cologne in Germany. I am a medical oncologist with expertise in personalized lung cancer care.

About 10% of patients with advanced EGFR-mutated lung cancer suffer from leptomeningeal disease. While this disease manifestation in non-small-cell lung cancer is generally associated with a particularly poor prognosis, with survival times of only a few months, the question arises whether treatment with specific tyrosine kinase inhibitors might enable a better disease control. Most studies evaluating the efficacy of 1st and 2nd generation EGFR-TKIs in leptomeningeal disease were retrospective and difficult to interpret, given the heterogeneity of the disease as well as of the preceding treatment procedures. Small prospective studies with patient numbers below 20 tested standard dose erlotinib or afatinib as well as high-dose pulsatile EGFR TKI treatment and reported disappointing results with survival times of around 4 months only.

The 3rd generation EGFR TKI osimertinib initially was approved for T790M positive failure of 1st and 2nd generation EGFR TKIs and is now commonly regarded as 1st line standard treatment for EGFR-mutated lung cancer based on a superior progression-free survival, overall survival and toxicity profile. In studies with primates and healthy volunteers, osimertinib has been shown to exert a higher blood-brain barrier permeability and a higher brain exposure compared with other TKIs. In the AURA clinical development program for osimertinib, 22 patients with T790M-positive relapse after EGFR TKI treatment and leptomeningeal disease were retrospectively identified, and an impressive median overall survival of 18.8 months was reported. A small prospective Japanese trial evaluated osimertinib in 13 patients with T790M-positive leptomeningeal disease which, however, could be confirmed only in 5 patients. Responses were seen in some patients, and the median progression free survival for all patients was reported with 7.2 months.

The BLOOM study part B, which is discussed in this podcast, is a multicenter phase I study evaluating osimertinib in EGFR-mutated lung cancer patients with leptomeningeal metastases and failure of previous EGFR TKI treatment. Study objectives were the assessment of clinical parameters like response, overall survival neurological status, and safety but also pharmacokinetics in blood and cerebrospinal fluid. Main inclusion criteria included confirmed diagnosis of EGFR Exon 19 deletion or L858R mutation and confirmation of leptomeningeal disease by positive cytology of cerebrospinal fluid and at least one leptomeningeal site assessable by MRI. There were two sequential cohorts, one unselected for the T790M mutation and with stable non-CNS disease at enrollment, and one for T790M positive patients without the requirement for stable non-CNS disease. Osimertinib dose was 160 mg once daily, which is twice the approved dose. Besides investigator-based response assessment, according to RECIST, leptomeningeal disease was also assessed by a neuroradiological blinded central review according to the RANO-LM working group criteria, which integrates clinical examination, cerebrospinal fluid cytology and neuraxis MRI.

41 patients from South Korea and Taiwan were included, 20 in the unselected and 21 in the T790M-positive cohort. About 70% of the patients had co-existing brain mets and about 50% prior radiotherapy. For 4 patients, no response data from the independent review were available.

The confirmed overall response rate for leptomeningeal disease was impressive at 62% as assessed by blinded independent review and nearly identical between both cohorts.  By comparison, the overall response rate was only 27% by investigator assessment, which, in turn, revealed a higher stable disease rate. Prior brain radiotherapy had no influence on efficacy. Median duration of response was comparable between blinded independent review and investigator, with 15.2 and 18.9 months, respectively. In about one third of the evaluable patients confirmed CSF clearance could be observed. PK analysis indicated that plasma concentration of osimertinib and its active metabolites reached steady state by day 15; the ratio for osimertinib exposure in cerebrospinal fluid vs. plasma was around 16%.

Surprisingly, only half of the patients had an abnormal neurological baseline assessment, most of them with mild symptoms. Symptom stabilization occurred in 54% during treatment; only 5% showed regression of neurological functions.

Overall, median progression-free survival, as assessed by the investigators, was 8.6 months and median overall survival 11 months. Progression-free survival and overall survival differed markedly between both cohorts. For instance, overall survival was 16.6 months in the unselected and 8.1 months in the selected group. Possibly, the requirement for stable non-CNS disease in the unselected group was partly responsible for the better survival outcome in this subset . However, this has to be interpreted cautiously in view of small patient numbers and large confidence intervals.

Osimertinib 160mg was well tolerated in the majority of patients with the known osimertinib side-effect profile. However, 24% of the patients suffered from adverse events grade 3 or more—possibly related to osimertinib, according to the investigators’ assessment. Dose reduction had to be performed in 12% and discontinuation of treatment in 22% of the patients due to adverse events. 17% of the patients had fatal events that did not appear to be causally related to osimertinib.

What can we learn from this study? This is the largest prospective study so far in this setting and osimertinib clearly shows clinical efficacy. The study methodology was sound, with response assessment by blinded independent review and based on RECIST criteria as well as on the RANO criteria established in particular for leptomeningeal disease. The overall response rate of leptomeningeal disease of around 60% and the duration of response of around 15 months is clinically relevant in particular, as it is correlated with improvement or at least neurological stabilization in most patients. Although the toxicity of the treatment is substantially higher than reported in osimertinib trials so far, it is manageable, and the risk/benefit ratio appears to be favorable.

What are the limitations of the study? Patient numbers are small, and the patients are heterogeneous with respect to several important factors such as pretreatment whole-brain radiotherapy, occurrence of simultaneous CNS metastases and neurological symptoms. Thus, absolute values for efficacy have to be interpreted cautiously, and comparison with already published trials remains difficult. Also, unfortunately in view of the toxicity, the question remains open whether the 160mg dose, which is not approved, is actually necessary. Finally, since osimertinib increasingly becomes the first-line treatment standard in EGFR-mutated lung cancer, the number of patients with failure of 1st- or 2nd-generation EGFR TKI treatment will decrease.

Despite these limitations, the trial provides the most convincing data so far in this special patient population and, in my opinion, defines  an important new option to consider for patients with EGFR-mutated lung cancer and leptomeningeal disease after failure of previous EGFR TKI treatment.

This concludes this JCO Podcast. Thank you for listening.