COMMENTARY Intratumoral Lymphatic Vessels: A Case of Mistaken Identity or Malfunction?

Metastasis is the major cause of mortality from malignant tumors. Metastatic cancer cells spread to various organs via the vascular system (hematogenic metastasis) and/or the lymphatic system (lymphogenic metastasis). Compared with our under-standing of a tumor’s vascular system, our understanding of its lymphatic system is minimal, although it has been known for some time that lymphatic vessels are present in the margins of animal and human tumors. Indeed, invasion of peritumor lym-phatics is considered to be a poor prognostic factor for patients with some tumors (e.g., breast, colorectal, and endometrial can-cers), and lymphatic metastasis is a major cause of morbidity and mortality for others (e.g., melanoma, head and neck, lung, and cervical cancers; www.uptodate.com). For nearly a century, it has been a hotly debated issue whether anatomically defined lymphatic vessels are present within solid tumors (1) and, if so