Tumor-to-tumor metastasis (TTM) is a relatively rare but well-documented phenomenon. When malignant tumor metastasizes to an intracranial tumor, meningiomas are most often the recipient; and breast or lung carcinoma the most common donor (primary tumor). The diagnosis of TTM can be made only by histopathological examination. Awareness of TTM is essential in clinical practice for timely diagnosis and early detection of malignant disease. The pathogenesis of TTM is related to various factors including vascularity and indolent growth of the recipient tumor; and simultaneous occurrence of the particular donor and recipient tumors (most notably breast carcinoma and meningioma). Most essential for understanding pathogenesis, however, are current concepts in the pathogenesis of metastatic cancer, an edifice rising on the concept of “seed and soil” expressed by Paget in 1889. The recently developed metastatic niche model is built on “seed and soil” theory, and describes the evolution of a conducive microenvironment in which disseminated tumor cells engraft and proliferate at the secondary sites. Early interventions that target both the disseminating seed and the metastatic soil may enable improvements in prognosis of malignant tumors.