70P Invasive lobular breast cancer (ILC), an overlooked subtype in clinical trials

ILC represents ∼15% of all breast cancers (BC). Clinical, histological and molecular differences between ILC and BC of non-special type support the idea of ILC as a separate entity. Unfortunately, evidence on treatment efficacy for ILC is often lacking. We aimed to map out the lack of documentation and representation of patients with ILC in clinical drug trials (CT), trials investigating gene expression profiles (GEPs) and molecular screening programs (MS). Phase III and IV CT for novel BC treatments were identified on clinicaltrials.gov and Pubmed by use of keywords linked to treatment strategies, GEPs and MS and ‘breast cancer’. CT were included if a manuscript was available on 15.01.2023. Inclusion and exclusion criteria were reviewed to see if patients with ILC or non-measurable disease were excluded. Documentation of ILC was assessed and if reported, percentage of ILC, central pathology for ILC and ILC subgroup analyses were evaluated. In total, 80 CT were included of which 14 were neoadjuvant, 11 adjuvant and 55 metastatic. One CT restricted inclusion to patients with NST. Non-measurable disease was an exclusion criterium in 20% of the CT (14.3% neoadjuvant and 25.2% metastatic) and non-measurable disease with the exception of bone-only disease was excluded in 30.9% of the metastatic CT. Inclusion of patients with ILC was documented in 11/80 CT (13.8%: 35.7% neoadjuvant, 9.1% adjuvant, 9.1% metastatic). Inclusion rates varied between 2.0 and 16.3%. Only 2/11 CT had specific sub-analyses on ILC and no CT reported central pathology for ILC. The initial manuscript of 6/7 of the GEPs and 1/3 of the MS was lacking ILC information. Secondary retrospective analyses for ILC are available for 5/6 remaining GEPs. ILC is greatly overlooked in the majority of CT with poor representation, documentation and lack of specific sub-analyses. Eligibility criteria and definitions of treatment response do not reflect the unique biology and clinical course of ILC. Thus, conclusions about efficacy with respect to ILC cannot accurately be drawn. It is critical that these gaps in inclusion and study of ILC are closed. ILC deserves much more attention from both clinical investigators and pharmaceutical industries.