Background Patients with human epidermal growth factor receptor 2-positive (HER2-positive) cancers have a high incidence of central nervous system (CNS) spread, but unfortunately systemic trastuzumab which targets the HER2 receptor has little CNS penetration. The purpose of this study was to determine the maximum tolerated dose of intrathecal trastuzumab and its efficacy in patients with HER2-positive LMD. Methods This multicenter study enrolled 34 LMD patients in a combined Phase I/II study in treating patients with intrathecal trastuzumab. Any HER2-positive histology was allowed in the Phase I; the Phase II was limited to HER2-positive breast cancer. Results Intrathecal trastuzumab was well tolerated, with one dose limiting toxicity of grade 4 (arachnoiditis) occurring at the 80 mg twice weekly dose. The recommended Phase II dose was 80 mg intrathecally twice weekly. Twenty-six patients at dose level 80mg were included in evaluation for efficacy: partial response was seen in 5 (19.2%) patients, stable disease was observed in 13 (50.0%), and 8 (30.8%) of the patients had progressive disease. Median overall survival (OS) for Phase 2 dose treated patients was 8.3 months (95% CI 5.2 to 19.6). The Phase II HER2-positive breast cancer patients median OS was 10.5 months (95% CI 5.2 to 20.9). Pharmacokinetic (PK) studies were limited in the setting of concurrent systemic trastuzumab administration, however, did show stable CSF concentrations with repeated dosing suggest that trastuzumab does not accumulate in the CSF in toxic concentrations. Conclusion This study suggests promise for potentially improved outcomes of HER-positive LMD patients when treated with intrathecal trastuzumab while remaining safe and well-tolerated for patients.

The study population within phase III clinical trials leading to approval of new cancer agents should ideally more closely mirror the population who will ultimately receive these agents. Although the number of females participating in clinical trials has increased over the past several decades, females are still under-represented in preclinical studies, in early phase clinical trials and even in some later phase cancer clinical trials. In the USA, this is particularly true for women from minority populations and elderly women. In this review, we review gender and sex disparities in cancer trials, the reasons for these disparities, the barriers to clinical trial enrolment and ways to improve diversity in cancer clinical trials.