Rectal carcinoma is uncommonly associated with systemic metastases in the absence of liver metastases, reflecting the predilection for spread via the portal system. Occasionally, isolated lung metastases are seen, which are usually attributed to spread via the portosystemic anastomoses in the distal rectum. However, myelophthisis is an unreported complication of rectal cancer as an isolated form of systemic failure. We present a case of fatal myelophthisis associated with otherwise localized rectal carcinoma secondary to metastatic rectal cancer. This observation led to the hypothesis that spread to the bone marrow occurred via a "third circulation," the Batson plexus, a network of deep pelvic veins with rich anastomoses to the vertebral plexus.