IMG-56. Primary tumor type influences anatomical destination in large metastases to the brain and shows a preference for the posterior fossa

The “seed and soil” hypothesis has driven considerable interest in understanding the unique influences of the primary tumor microenvironment on ultimate destination. Given their known predilection for CNS metastasis, a significant amount of work has focused on breast and lung cancers–with less attention to other primary types. Moreover, the influence of tumor volume on anatomical distributions within the brain is also unknown. As such, data regarding the characteristics of large metastatic lesions (>2cm) is scarce. We sought to map the anatomic distribution of metastases to the brain for multiple primary sites of origin for large metastatic lesions (>2cm) treated with stereotactic radiosurgery. 1218 lesions from 619 patients were obtained from a large retrospectively collected database for individuals undergoing treatment with stereotactic radiosurgery (SRS). Lesion centroids were calculated from T1 weighted post-contrast imaging and their precise locations on a template brain obtained and displayed (Montreal Neurological Institute Atlas (MNI305)). Expected metastatic rates were calculated based on relative region volume as a percentage of total brain volume. Metastatic lesions measuring at least 2 cm in one or more dimensions were included. Six different primary tumor types were highlighted: gastrointestinal (esophageal, colorectal, gastric, etc; 64 lesions), lung (non-small cell; 319 lesions), lung (small cell; 79 lesions), melanoma (281 lesions), breast (276 lesions), and renal (107 lesions). Breast, GI, and lung (small cell and non-small cell) cancers were identified at a greater-than-expected proportion in the posterior fossa (based on relative volume). Melanoma lesions appeared underrepresented in the posterior fossa. Metastases from renal cancer appeared overrepresented in the temporal lobe. Large metastases have an overall predilection for the posterior fossa. An infratentorial preference may suggest unique characteristics of the posterior fossa including arterial supply, venous drainage, or the unique cytoarchitecture of the cerebellum and brain stem. Metastatic melanoma appeared less likely to be in the posterior fossa. Metastatic renal lesions showed a preference for the temporal lobe.