The spinal distribution of metastatic renal cell carcinoma: Support for locoregional rather than arterial hematogenous mode of early bony dissemination.

742 Background: To investigate the distribution of spinal metastasis in metastatic renal cell carcinoma (mRCC) and to explore relationships between biological and clinical factors and patterns of spinal spread. Methods: An institutional database was queried to identify patients with mRCC and spinal metastatic involvement from June 2005 – November 2018. A blinded radiologist examined all cross-sectional imaging involving the spine and scored each level for absence or presence of disease. Clinical and biologic features including primary tumor size and degree of spinal and non-bony metastatic involvement (including regional lymph node and distant deposits) were collected. Spinal distributions were evaluated by the Kolmogorov Smirnov test and compared across radiographic and clinical parameters. Results: One-hundred patients with 685 spinal levels involved by mRCC were evaluated. A nonuniform spatial distribution was observed across the cohort; a preponderance of thoracolumbar involvement was noted with the mode at L3 (p<0.001). No difference in metastatic distribution was observed in right versus left-sided tumors. Tumors <4cm compared to >7cm, patients who had distant spread versus bone-only disease, and patients with increasing number of spine levels involved (1 versus >5 levels) had a significantly different distribution (p<0.001 for all comparisons). Smaller tumor size, distant spread, and greater number of involved levels appeared to have a more uniform distribution of spinal metastasis. Conclusions: These data support a dominant locoregional as opposed to arterial hematogenous mechanism for the early dissemination of mRCC to the spine. This is concordant with the theory of the valveless Batson plexus acting as a conduit for such spread, as the kidneys are compartmentally distinct from, but reside just anterior to the spine at L1-L3. Characterizations of the biologic molecular features contributing to osseous tropism and aggressive tumor biology (as seen in the subset of patients with uniform spread, such as outlier patients with small tumors), have implications for surveillance and are an area of active investigation.