

Etiology of CUP

The reason why a primary tumor may be difficult or impossible to find may be due to different causes:

  • The primary tumor once existed and spontaneously disappeared, however, the metastatic cells are still active, creating tumors and causing symptoms.
  • The primary tumor produces metastatic cells continually and in such a large volume that there is no net growth of the primary tumor. The tumor remains small and difficult to detect. These metastatic manifestations grow causing symptoms.
  • There is no primary tumor, but the impression of metastasis is due to normal cells in abnormal locations undergoing malignant transformation. Examples may be epithelial cells or nevus cells in lymph nodes.
