Malignant tumors are capable of spreading throughout the body either by direct invasion or through the bloodstream and lymphatic system, causing metastases in lymph nodes as well as in distant organs and tissues.
Most malignant tumors are named after the organ in which they originate, such as breast cancer or lung cancer. Malignant tumors arising in the mucous membranes of hollow organs (such as the esophagus, stomach, colon, and bladder) are called epithelial cancers, while tumors of solid organs (such as bone) are called sarcomas.
Tumors are also characterized according to their tissue structure, or histology (e.g., adenocarcinoma, squamous cell carcinoma, small-cell carcinoma, and non-small-cell carcinoma).
In addition, tumors are classified by stage according to the extent of their spread. For this, a special TNM classification system is used, where T indicates the size and local extent of the primary tumor, N refers to lymph node involvement, and M denotes the presence of distant metastases.
At a minimum, the structure and stage of the tumor must be known before starting treatment. However, for modern targeted therapies, more detailed information is also needed about the tumor’s other biological characteristics and potential molecular treatment targets.
