Incidence of hippocampal metastases in non-small-cell lung cancer

Patients with locally advanced non-small-cell lung cancer (LA-NSCLC) develop brain metastases in 25-50% of cases during the course of their disease. Data on the incidence of metastases occurring in the hippocampus/perihippocampal zones are limited. This is important when considering hippocampal-sparing brain radiation (HS-BR), a method that could potentially reduce the neurocognitive impact of such treatment. The aim of this study was to assess the incidence of hippocampal/perihippocampal metastases in a cohort of patients with advanced NSCLC treated at our institution.

This retrospective cohort study included NSCLC patients discussed at our institutional lung cancer multidisciplinary meeting between 2000 and 2016. MRI and contrast-enhanced CT (ceCT) brain images were reviewed to assess the incidence of hippocampal/perihippocampal metastases including metastases within the hippocampal subgranular zone and a 5 mm margin (hippocampal avoidance region) defined as per the RTOG 0933 study.

Of 2146 patients reviewed, 357 (16.6%) had brain metastases. A total of 335 patients had available MRI/ceCT brain images for review. Thirty (9%) patients had brain metastases in the hippocampal avoidance region, 8 (2.4%) with hippocampal metastases and 22 (6.6%) with perihippocampal metastases. Univariate analyses did not show an association between developing metastases in the hippocampal avoidance region and age (P = 0.75), gender (P = 0.91) and tumour type (P = 0.298).

The incidence of metastases in the hippocampal avoidance region in our large cohort of patients was 9%. With low rates of metastases in this region, HS-BR can be considered a feasible option in the management of patients with advanced NSCLC.