Unraveling Tumor-to-Tumor Metastasis: Insights into Pathogenesis, Diagnostic Challenges, and Treatment Modalities.

Tumor-to-tumor metastasis (TTM) is defined as the metastasis of one distinct malignancy to another independent tumor without directly extending into the substance of a histologically distinct and separate tumor. TTM is an extremely rare phenomenon that constitutes a very small percentage of all tumor metastases. The detailed histogenic mechanisms of TTM remain unclear.