Tumor-to-Tumor Metastasis in a Patient With Hemangioblastoma Unrelated to von Hippel-Lindau Disease: A Case Report and Review of the Literature.

Tumor-to-tumor metastasis (TTM) is a rare phenomenon in which one malignant tumor ("donor") metastasizes to another benign tumor ("recipient"). In the central nervous system (CNS), meningioma is considered one of the most frequent recipients, while hemangioblastoma (HGB) has also been reported, typically in association with von Hippel-Lindau (VHL) disease. A 61-year-old woman with a history of bilateral breast cancer treated 17 years earlier presented with right-sided ataxic hemiparesis. Magnetic resonance imaging revealed a gadolinium-enhanced mass in the right cerebellum, initially diagnosed as a metastatic brain tumor. Despite stereotactic radiotherapy, symptoms persisted and the lesion enlarged. Surgical resection was performed via the occipital trans-tentorial approach. Intraoperative findings revealed a reddish, vascular tumor with a xanthochromic area. Complete resection was achieved. Pathological examination confirmed two distinct components: HGB and metastatic breast carcinoma, establishing the diagnosis of TTM. No evidence of VHL was identified. The pathogenesis of TTM remains unclear, although factors such as recipient tumor vascularity and a favorable microenvironment are proposed. The rarity of non-VHL-associated TTM in HGB emphasizes the need for further case accumulation, to clarify the underlying mechanisms. We report the first description of TTM involving metastatic breast cancer to a sporadic HGB in the CNS, unrelated to VHL. This case highlights the importance of considering TTM among the differential diagnoses for CNS tumors, even in the absence of VHL.